Ansi Mh16.1 2012(r2019).pdf [8lyrvmjyn20d] (2022)

ANSI MH16.1: 2012(R2019)

Specification for the Design, Testing and Utilization of Industrial Steel Storage Racks Abstract: The standard applies to industrial pallet racks, movable shelf racks, and stacker racks made of cold-formed or hot-rolled steel structural members. It does not apply to other types of racks, such as drive-in or drive-through racks, cantilever racks, portable racks, etc. or to racks made of material other than steel.

An Industry Group of MHI 8720 Red Oak Blvd., Suite 201 Charlotte, NC 28217-3992 [emailprotected]

© 2019 by MHI All rights reserved.

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American National Standard Approval of an American National Standard requires verification by ANSI that the requirements for due process, consensus, and other criteria for approval have been met by the standards developer. Consensus is established when, in the judgment of the ANSI Board of Standards Review, substantial agreement has been reached by directly and materially affected interests. Substantial agreement means much more than a simple majority, but not necessarily unanimity. Consensus requires that all views and objections be considered, and that a concerted effort be made toward their resolution. The use of American National Standards is completely voluntary; their existence does not in any respect preclude anyone, whether he has approved the standards or not, from manufacturing, marketing, purchasing, or using products, processes or procedures not conforming to the standards. The American National Standards Institute does not develop standards and will in no circumstances give an interpretation of any American National Standard. Moreover, no person shall have the right or authority to issue an interpretation of an American National Standard in the name of the American National Standards Institute. Requests for interpretations should be addressed to the sponsor whose name appears on the title page of this standard. CAUTION NOTICE: This American National Standard may be revised or withdrawn at any time. The procedures of the American National Standards Institute require that action be taken periodically to reaffirm, revise or withdraw this standard. Purchasers of American National Standards may receive current information on all standards by calling or writing the American National Standards Institute.

Published by

Rack Manufacturers Institute An Industry Group of MHI 8720 Red Oak Blvd., Suite 201, Charlotte, NC, 28217-3992 Telephone: (704) 676-1190 www.mhi.org/rmi [emailprotected]

© 2019 by Material Handling Industry All rights reserved. No part of this publication may be reproduced in any form, in an electronic retrieval system or otherwise, without prior written permission of the publisher, RMI. Printed in the United States of America.

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ANSI MH16.1:2012(R2019)

American National Standard

Specification for the Design, Testing and Utilization of Industrial Steel Storage Racks

Rack Manufacturers Institute (RMI) An Industry Group of MHI

Approved September 12, 2019 American National Standards Institute, Inc.

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American National Standard Specification for the Design, Testing and Utilization of Industrial Steel Storage Racks

ANSI MH16.1: 2012(R2019)

Disclaimer FOREWORD. This Standard, approved by ANSI on January 13, 2012 and reaffirmed by ANSI on September 12, 2019, was developed under Material Handling Industry’s (MHI) ANSI approved procedures, and represents suggested design practices and operational requirements for Industrial Steel Storage Racks. It was developed by the Rack Manufacturers Institute (RMI), and is intended to provide useful information and guidance for owners, users, designers, purchasers and/or specifiers of material handling equipment or systems. It is advisory only and should only be regarded as a simple tool that its intended audience may or may not choose to follow, adopt, modify, or reject. The following information does not constitute a comprehensive safety program, cannot guard against pitfalls in operating, selecting and purchasing such a system, and should not be relied upon as such. Such a program should be developed, and an independent adviser should be consulted in doing so. VOLUNTARY. The use of this document is completely voluntary. Its existence does not in any respect preclude anyone, whether it has approved this Standard or not, from following procedures and assuming responsibilities not conforming to this Standard. DISCLAIMER OF LIABILITY. MHI, RMI and their members assume no responsibility and disclaim all liability of any kind, however arising, as a result of acceptance or use or alleged use of this Standard. Anyone using this Standard specifically understands and agrees that MHI, RMI, their members, officers, agents, and employees shall not be liable under any legal theory of any kind for any action or failure to act with respect to the design, erection, installation, manufacture, and preparation for sale, sale, characteristics, features, or delivery of anything covered by this Standard or any other activity covered by this Standard. Any use of this information must be determined by the user to be in accordance with applicable federal, state, and local laws and regulations. DISCLAIMER OF WARRANTY. MHI, RMI and their members make NO WARRANTIES of any kind, express or implied, in connection with the information in this brochure and SPECIFICALLY DISCLAIM ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND OF FITNESS FOR PARTICULAR PURPOSE. INDEMNIFICATION. By referring to or otherwise employing this Standard, its user agrees to defend, protect, indemnify, and hold MHI, RMI, their members, officers, agents, and employees harmless from and against all claims, losses, expenses, damages, and liabilities, direct, incidental, or consequential, arising from acceptance or use or alleged use of this Standard, including loss of profits and reasonable attorneys' fees which may arise out of the acceptance or use or alleged use of this document. The intent of this provision is to absolve and protect MHI, RMI, their members, officers, agents, and employees from any and all loss relating in any way to this document, including those resulting from the user's own negligence. FOR Questions Contact: Material Handling Industry, 8720 Red Oak Blvd., Suite 201, Charlotte, NC 28217-3992; [emailprotected]

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American National Standard Specification for the Design, Testing and Utilization of Industrial Steel Storage Racks

Foreword

ANSI MH16.1: 2012(R2019)

[This foreword is not part of American National Standard MH16.1:2012(R2019)]

RACK MANUFACTURERS INSTITUTE The Rack Manufacturers Institute (RMI) is an independent incorporated trade association affiliated with the Material Handling Industry. The membership of RMI is made up of companies which produce the preponderance of industrial steel storage racks and Welded Wire Rack Decking used in the USA. RMI maintains a public website at www.MHI.org/RMI that has information about storage racks and the RMI members including ordering information for literature and a section for frequently asked questions. All inquiries concerning the Specification should be directed in writing to the RMI Engineering Committee, 8720 Red Oak Boulevard, Suite 201, Charlotte, NC 28217.

MATERIAL HANDLING INDUSTRY The Material Handling Industry (MHI) provides RMI with certain services and, in connection with this Specification, arranges for its production and distribution. Neither the Material Handling Industry nor its officers, directors, or employees have any other participation in the development and preparation of the information contained in the Specification.

SPECIFICATION - HISTORY In the interest of improved uniformity of rack performance and enhanced public safety, the RMI published in 1964 its first “Minimum Engineering Standards for Industrial Storage Racks”, and now publishes this Specification. It was developed and promulgated by the RMI with the sole intent of offering information to the parties engaged in the engineering, manufacturing, marketing, purchasing, installation, inspection, permitting or use of such racks. Since 1964, mechanized storage systems have grown very rapidly both in size and height with new and modified types of racks having been developed. To reflect this rapid development and to assure adequate safety and performance of modern rack structures, the RMI decided early in 1971 to replace its original standards by a more detailed and comprehensive specification. Professors George Winter and Teoman Pekoz of Cornell University were retained to assist the Rack Standard Development Project Committee in producing such a document. The members of the Material Handling Institute, Inc. were the sponsors. In 1972, the “Interim Specification for the Design, Testing and Utilization of Industrial Steel Storage Racks” was adopted by the Rack Manufacturers Institute at their annual fall meeting. The specification was then submitted to the American National Standards Institute for their review and acceptance. In 1974, the Interim Specification with minor changes was accepted as American National Standard ANSI MH 16.1-1974. The Rack Manufacturers Institute together with its sponsors from the Material Handling Institute, Inc., retained Professors Winter and Pekoz to continue testing rack components plus perform full scale tests on typical storage rack structures. A number of the test results have been analyzed, and it was considered necessary to rewrite the 1972 Interim Specification to include the knowledge gained from the analysis of those tests. The 1972 Interim Specification was rewritten by the Rack Standards Subcommittee with the assistance of Professors Winter and Pekoz. Design parameters relating to drive-in and drive-through racks have been removed from the Specification until drive-in and drive-through rack test results could be analyzed more thoroughly; perhaps more testing would be required. Movable-shelf racks were added to the Specification. V12a

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American National Standard Specification for the Design, Testing and Utilization of Industrial Steel Storage Racks

ANSI MH16.1: 2012(R2019)

As a result of additional testing and analytical research, the RMI revised the 1972 Specification. The ANSI MH 16.1-1974 was withdrawn in deference to the 1979 Specification. More additions and revisions prompted the RMI to publish the 1985 Specification. Subsequent testing and research by Dr. Pekoz was the basis of the changes resulting in the 1990 Specification. From 1990 to 1997, due to continuing changes, specifically as they relate to seismic analysis and other model building code issues, the Specification Advisory Committee, the Seismology Committee and the RMI Engineering Committee working again with Dr. Pekoz and several highly regarded members of the code community and various other members of similar groups throughout the world, conducted extensive testing and parametric analysis. Findings resulted in the 1997 Specification. In addition to the state-of-the-art benefit from the ongoing testing and analysis, the 1997 Specification was expanded to include complete treatment of seismic design considerations so that the Specification could be more easily incorporated by reference into various model building and design codes. In 1999, the Membership of RMI acted to create a Voluntary Certification Program known as the R-MARK. The R-Mark is a license earned by a manufacturer following a rigorous review by independent professional engineers of tests and load capacity calculations performed by the manufacturer consistent with the RMI/ANSI Specification. Continued testing and parametric studies resulted in the 2002 Specification. In 2004 the 2002 RMI Specification and Commentary were adopted as American National Standard ANSI MH 16.1-2004. The 2008 RMI Specification (ANSI MH 16.1-2008) incorporated the results from the FEMA 460 document, which was published in September, 2005. In addition, the symbol and nomenclature tables were added. The seismic section was updated going from the old A a and Av values to the current Ss and S1 values utilized by the USGS. A section on Connection Rotational Capacity was added. The Column Base Plate section was updated. A section on shims was added. A section on Pick Modules and Rack Supported Platforms was added. The section on Automated and Manual Storage and Retrieval Systems was taken out of the appendix and incorporated into the Specification. A section for Cyclic Testing of Beam-toColumn Connections was added.

SPECIFICATION - 2012 EDITION The use of this Specification is permissive, not mandatory. Voluntary use is within the control and discretion of the user and is not intended to, and does not in any way limit the ingenuity, responsibility or prerogative of individual manufacturers to design or produce industrial steel storage racks that do not comply with this Specification. The RMI has no legal authority to require or enforce compliance with the Specification. This advisory Specification provides technical guidelines to the user for his specific application. Following the Specification does not assure compliance with applicable federal, state, or local regulations and codes. This Specification is not binding on any person and does not have the effect of law. The RMI and the Material Handling Industry do not take any position regarding any patent rights or copyrights which could be asserted with regard to this Specification, and does not undertake to insure anyone using this Specification against liability, nor assume any such liability. Users of this Specification are expressly advised that determination of the validity of any such copyrights, patent rights, and risk of infringement of such rights is entirely their own responsibility.

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American National Standard Specification for the Design, Testing and Utilization of Industrial Steel Storage Racks

ANSI MH16.1: 2012(R2019)

In the interest of safety, all users of storage racks are advised to regularly inspect and properly maintain the structural integrity of their storage rack systems by assuring proper operational, housekeeping and maintenance procedures. Users of the Specification must rely on competent advice to specify, test and/or design the storage rack system for their particular application. This Specification is offered as a guideline. If a user refers to, or otherwise employs, all or any part of the Specification, the user is agreeing to follow the terms of indemnity, warranty disclaimer, and disclaimer of liability.

REAFFIRMATION - 2019 EDITION This American National Standard was reaffirmed by ANSI on September 12, 2019. During the reaffirmation process, RMI references a new source of the variables SS and S1 in Section 2.6.3.2. The 2012 version of this Specification included a link to a United States Geological Survey (USGS) website that is no longer maintained. The 2019 version includes a reference to https://seismicmaps.org where this data can be obtained. The 2019 edition also refers to the 2019 reaffirmation and that Material Handling Industry of America and Material Handling Industry now go by the acronym MHI. No additional changes were made to the 2019 edition.

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American National Standard Specification for the Design, Testing and Utilization of Industrial Steel Storage Racks

ANSI MH16.1: 2012(R2019)

TABLE OF CONTENTS SYMBOLS.................................................................................................................x NOMENCLATURE.....................................................................................................xv 1. GENERAL ...................................................................................................... 1 1.1

SCOPE ...................................................................................................... 1

1.2

MATERIALS ................................................................................................ 1

1.3

APPLICABLE DESIGN SPECIFICATIONS .......................................................... 1

1.4

INTEGRITY OF RACK INSTALLATIONS ............................................................ 1

1.4.1

Owner Maintenance .......................................................................... 1

1.4.2

Plaque ............................................................................................... 2

1.4.3

Conformance ..................................................................................... 2

1.4.4

Load Application and Rack Configuration Drawings ......................... 2

1.4.5

Multiple Configurations ...................................................................... 2

1.4.6

Movable-Shelf Rack Stability ............................................................. 3

1.4.7

Column Base Plates and Anchors ..................................................... 3

1.4.8

Small Installations ............................................................................. 3

1.4.9

Rack Damage ................................................................................... 3

1.4.10 Racks Connected to the Building Structure ....................................... 3 1.4.11 Out-of-plumb and Out-of-straight Limits ............................................ 3 2. LOADING ....................................................................................................... 4 2.1

LOAD COMBINATIONS FOR THE ASD DESIGN METHOD ................................. 4

2.2

LOAD FACTORS AND COMBINATIONS FOR THE LRFD DESIGN METHOD ........... 5

2.3

VERTICAL IMPACT LOADS ............................................................................ 5

2.4

HORIZONTAL FORCES ................................................................................. 5

2.5

WIND LOADS.............................................................................................. 6

2.6

EARTHQUAKE LOADS .................................................................................. 6

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2.6.1

General ............................................................................................. 6

2.6.2

Minimum Seismic Forces .................................................................. 7

2.6.3

Calculation of Seismic Response Coefficient .................................... 9

2.6.4

Connection Rotational Capacity ...................................................... 20

2.6.5

Seismic Displacement ..................................................................... 20 vi

American National Standard Specification for the Design, Testing and Utilization of Industrial Steel Storage Racks

ANSI MH16.1: 2012(R2019)

2.6.6

Seismic Separation ......................................................................... 21

2.6.7

Vertical Distribution of Seismic Forces ............................................ 21

2.6.8

Horizontal Shear Distribution ........................................................... 22

2.6.9

Overturning ..................................................................................... 22

2.6.10 Concurrent Forces........................................................................... 22 3. DESIGN PROCEDURES ............................................................................. 23 4. DESIGN OF STEEL ELEMENTS AND MEMBERS ..................................... 23 4.1

COLD-FORMED STEEL MEMBERS .............................................................. 23

4.1.1

Properties of Sections ..................................................................... 23

4.1.2

Flexural Members............................................................................ 23

4.1.3

Concentrically Loaded Compression Members ............................... 23

4.2

HOT-ROLLED STEEL COLUMNS ................................................................. 24

5. BEAM DESIGN ............................................................................................ 24 5.1

CALCULATIONS ........................................................................................ 24

5.2

CROSS SECTION ...................................................................................... 24

5.3

DEFLECTIONS .......................................................................................... 24

5.4

BEAM-TO-COLUMN CONNECTIONS ............................................................. 25

5.4.1

General ........................................................................................... 25

5.4.2

Beam Locking Device...................................................................... 25

5.4.3

Movable-Shelf Racks ...................................................................... 25

5.5

PALLET SUPPORTS ................................................................................... 25

5.6

WELDED-WIRE RACK DECKING ................................................................. 25

6. UPRIGHT FRAME DESIGN ......................................................................... 25 6.1

DEFINITION .............................................................................................. 25

6.2

GENERAL................................................................................................. 25

6.2.1

Upright frames and multi-tiered portal frames ................................. 25

6.2.2

Connections .................................................................................... 26

6.3

EFFECTIVE LENGTHS ................................................................................ 26

6.3.1 Flexural Buckling in the Direction Perpendicular to the Upright Frames……………………………………………………………………………..26 6.3.2 V12a

Flexural Buckling in the Plane of the Upright Frame ....................... 26 vii

American National Standard Specification for the Design, Testing and Utilization of Industrial Steel Storage Racks

ANSI MH16.1: 2012(R2019)

6.3.3

Torsional Buckling ........................................................................... 27

6.3.4

Diagonals and Horizontals .............................................................. 27

6.4

STABILITY OF TRUSSED-BRACED UPRIGHT FRAMES .................................... 28

7. COLUMN BASE DESIGN ............................................................................ 29 7.1

COLUMN BASE PLATES .............................................................................. 29

7.1.1

Bearing on concrete ........................................................................ 29

7.1.2

Base plate design ............................................................................ 29

7.1.3

Maximum Considered Earthquake Base Rotation ........................... 30

7.1.4

Shims .............................................................................................. 31

7.2

SLAB AND SUBGRADE EVALUATION ............................................................ 31

7.3

ANCHOR BOLTS ....................................................................................... 31

7.3.1

Anchor Bolt Design.......................................................................... 31

7.3.2

Periodic Inspection of Anchor Bolt Installation ................................ 31

8. SPECIAL RACK DESIGN PROVISIONS..................................................... 32 8.1

OVERTURNING ......................................................................................... 32

8.2

CONNECTIONS TO BUILDINGS .................................................................... 32

8.3

INTERACTION WITH BUILDINGS ................................................................... 32

8.4

PICK MODULES AND RACK SUPPORTED PLATFORMS ................................... 33

8.4.1

Posting of Design Loads ................................................................. 33

8.4.2

Design Requirements ...................................................................... 33

8.4.3

Rack Supported Platform and Pick Module Walkways .................... 33

8.4.4

Stairways......................................................................................... 35

8.4.5

Product Fall Protection .................................................................... 35

8.5

AUTOMATED STORAGE AND RETRIEVAL SYSTEMS (STACKER RACKS)........... 36

8.5.1

Tolerances (1.4.11) ......................................................................... 36

8.5.2

Vertical Impact Loads (2.3) ............................................................. 36

8.5.3

Horizontal Loads (2.4) ..................................................................... 36

8.5.4

Wind (2.5) and Snow Loads (2.1) .................................................... 36

8.5.5

Deflections (5.3) .............................................................................. 36

8.5.6

Rack Compatibility with the Equipment ........................................... 36

9. TEST METHODS ......................................................................................... 36 V12a

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American National Standard Specification for the Design, Testing and Utilization of Industrial Steel Storage Racks

9.1

ANSI MH16.1: 2012(R2019)

GENERAL................................................................................................. 36

9.1.1

Testing Apparatus and Fixtures ...................................................... 37

9.1.2

Instrumentation ............................................................................... 37

9.1.3

Reduction and Presentation of Test Data........................................ 37

9.1.4

Evaluation of Tests for Determining Structural Performance ........... 38

9.2

STUB COLUMN TESTS FOR COLD-FORMED AND HOT-ROLLED COLUMNS ...... 38

9.2.1

Test Specimen and Procedure ........................................................ 38

9.2.2

Evaluation of Test Results ............................................................... 38

9.3

PALLET BEAM TESTS ................................................................................ 39

9.3.1

Simply Supported Pallet Beam Tests .............................................. 39

9.3.2

Pallet Beam in Upright Frames Assembly Test ............................... 40

9.4

PALLET BEAM-TO-COLUMN CONNECTION TESTS......................................... 41

9.4.1

The Cantilever Test ......................................................................... 41

9.4.2

The Portal Test ................................................................................ 42

9.5

UPRIGHT FRAME TEST .............................................................................. 42

9.5.1 Horizontal Load in the Direction Perpendicular to the Plane of the Upright Frame .............................................................................................. 43 9.5.2 Horizontal Load in the Direction Parallel to the Plane of Upright Frame………………………………………………………………………………44 9.6

CYCLIC TESTING OF BEAM-TO-COLUMN CONNECTIONS............... 44

9.6.1

General ........................................................................................... 44

9.6.2

Definitions ....................................................................................... 45

9.6.3

Test Subassemblage Requirements ............................................... 45

9.6.4

Essential Test Variables .................................................................. 45

9.6.5

Testing Procedure ........................................................................... 46

9.6.6

Loading History-General Requirements .......................................... 46

9.6.7

Instrumentation ............................................................................... 46

9.6.8

Material Testing Requirements ....................................................... 47

9.6.9

Test Reporting Requirements ......................................................... 47

9.6.10 Acceptance Criteria ......................................................................... 47 9.6.11 Evaluation of Test Results ............................................................... 47 10. V12a

REFERENCES TO THE TEXT ................................................................. 48 ix

American National Standard Specification for the Design, Testing and Utilization of Industrial Steel Storage Racks

ANSI MH16.1: 2012(R2019)

SYMBOLS SYMBOL

FIRST APPEARS IN

DEFINITION

SECTION A

Sum of the minimum net area (Anet columns of the upright frame

Ab

Cross-sectional area of a horizontal brace

6.4

Ad

Cross-sectional area of a diagonal brace

6.4

Ae

Effective area at the stress Fn

Anet min

Minimum cross-sectional area obtained by passing a plane through the column normal to the axis of the column

9.2.2

Cd

Deflection amplification factor

2.6.4

Cs

Seismic response coefficient

2.6.2

Cw

Torsional warping constant

D

Dead load

2.1

E

Earthquake (seismic) Load

2.1

E

Modulus of elasticity of steel

6.4

F

Joint spring constant

C5.2

F1

Lateral force at the first shelf level

2.6.7

Fa

Site coefficient defined in Table 2.6.3.2 (2).

Fc

Critical buckling stress

4.1.2

Fi

Portion of base shear induced at level i

2.6.8

Fn

Nominal buckling stress

F’p

Maximum allowable bearing stress

Fv

Site coefficient defined in Table 2.6.3.2 (3).

Fx

Lateral force at any level

2.6.7

Fy

Yield point used for design

9.2.2

H

Total lateral force above shelf elevation being evaluated

H

Horizontal load per beam

I

Impact loading on a shelf

2.1

I

Minimum net moment of inertia of the columns about the gravity axis of the upright frame perpendicular to the plane of the upright frame

6.4

Ib

The beam moment of inertia

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min.)

of the

6.4

4.1.3.1

4.1.3.1

2.6.3.2

4.1.3.1 7.2.1 2.6.3.2

C2.6.3 C9.4.2.3

x

C5.2

American National Standard Specification for the Design, Testing and Utilization of Industrial Steel Storage Racks

ANSI MH16.1: 2012(R2019)

Ibr

Moment of inertia of the horizontal brace about its own axis perpendicular to the plane of the upright frame

6.4

Ic

Minimum net moment of inertia of one column about its own major axis perpendicular to the plane of the upright frame

6.4

Ip

System importance factor

Ix

Column moment of inertia about the x-axis

C2.6.3

K

Effective length factor

6.3.1.2

Kb

Base rotational stiffness

Kt

Effective length factor for torsional buckling

6.3.3.2

Kx

Effective length factor for story buckling in the down-aisle direction

C2.6.4

L

Live load other than the pallets or products stored on the racks

2.1

L

Column span length

L

Span of the beam

C5.2

L

Clear span between shelf beams

C5.5

L

Distance between the centroid of the two columns parallel with the shelf beam

C9.4.2.3

Lb

Actual span of the pallet beams

C6.3.1.1

Lc1

Distance from the floor to the first beam level

C6.3.1.1

Lc2

Distance from the first beam level to the second beam level

C6.3.1.1

Lr

Roof live load

Lshort and Llong

Distance between column brace points

Lx, Ly and Lt

Unbraced lengths for column design, for bending about x- and y-axes and for torsion

Mb

Base moment

7.1.3

Me

Beam end moment

C5.2

N

Effective length of the base plate in the down-aisle direction

7.1.2.3

Nb

Number of base plate connections

C2.6.4

Nc

Number of beam-to-column connections

C2.6.4

P

Maximum load from pallets or products stored on the racks

2.1

PAverage

Maximum total weight of product expected on all beam levels in any row divided by the number of

2.6.2

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2.6.2

7.1.3

C2.6.3

2.1

xi

6.3.2.2 6.3

American National Standard Specification for the Design, Testing and Utilization of Industrial Steel Storage Racks

ANSI MH16.1: 2012(R2019)

beam levels in that row PMaximum

Maximum weight of product that will be placed on any one beam level in a row

2.6.2

Prf

Product load reduction factor (PAverage / PMaximum)

2.6.2

Papp

Portion of pallet or product load that is used to compute the seismic base shear

2.1

Pcr

Critical elastic buckling load

6.4

Pn

Nominal axial strength

4.2

Q

Capacity reduction factor for compressive members

R

Load from rain including ponding

R

Seismic response modification factor

R.F.

Reduction Factor

S

Snow load

SD1

Design spectral response acceleration parameter for 1second period, (2/3) SM1

2.6.3

SDS

Design spectral response acceleration parameter for a 0.2 second (short) period, (2/3) SMS

2.6.3

SM1

Maximum considered earthquake spectral response accelerations for 1second period

2.6.3.1

SMS

Maximum considered earthquake spectral response accelerations for a 0.2 second (short) period

2.6.3.1

Sc

Elastic section modulus of the net section for the extreme compression fiber times 1-0.5(1-Q)(Fc/Fy)Q

4.1.2

Se

Elastic section modulus of the net section for the extreme compression fiber times (0.5+Q/2)

4.1.2

Ss

Mapped spectral accelerations for a 0.2 second (short) period as determined by the USGS

2.6.3.2

S1

Mapped spectral accelerations for a 1-second period as determined by the USGS

2.6.3.2

T

Fundamental period of the rack structure in each direction under consideration

2.6.3

V

Seismic base shear

2.6.2

Vx

Seismic design shear at any level

2.6.8

W

Wind load

W

Total load on each beam

C5.2

W

Unit Load divided by the number of pallet supports under load

C5.5

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9.2.2 2.1 2.6.3 C9.4.2.3 2.1

2.1

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American National Standard Specification for the Design, Testing and Utilization of Industrial Steel Storage Racks

ANSI MH16.1: 2012(R2019)

Wi

Loads on each level of the structure that are used to compute the period, D + (0.67xP) + (0.25xL)

C2.6.3

Wpi

The weight on the rack that amplifies the drift

C2.6.4

Ws

Loads on the structure that are used to compute the horizontal base shear, D + (0.67xPrfxP) + (0.25xL)

2.6.2

a

Vertical distance between the horizontal brace axes

6.4

b

Horizontal distance between neutral axes of the columns

6.4

b

Width of the column (parallel to the flexure axis)

d

Depth of the bottom of the pallet

d

Depth of the column (perpendicular to the flexure axis)

C6.3.1.1

ec

Center of gravity of the load closest to the pallet support

C5.5

f 'c

Minimum 28-day compression strength of the concrete floor

7.1.1

g

Acceleration due to gravity

h

Distance from the floor to the top of the beam

hi or hx

Height from the base to level i or x

2.6.7

htotal

Height of the top shelf level

2.6.4

k

Upright frame stability coefficient based on location of the center of load

kb

Rotational stiffness of each base plate connection

C2.6.4

kbe

Beam end rotational stiffness

C2.6.4

kc

Rotation stiffness connection

kce

Bottom column end rotational stiffness

l

Total height of the upright frame

wi or wx

Portion of the total gravity load of the rack, located or assigned to the bottom shelf level, level i or x

Seismic Product Load Coefficient

Sway deflection corresponding to a lateral load of 2H

Δi

Total lateral displacement at level, i

C2.6.3

Δi,1

Primary deflection just below the level being evaluated

C2.6.3

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of

C6.3.1.1 C5.5

C2.6.3

each

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beam-to-column

C9.4.2.3

6.4

C2.6.4 C2.6.4 6.4 2.6.7 2.1 C9.4.2.3

American National Standard Specification for the Design, Testing and Utilization of Industrial Steel Storage Racks

ANSI MH16.1: 2012(R2019)

Δp

Primary story drift

Δs

Seismic displacement at height of the top shelf

2.6.4

θD

Rotational seismic demand of the beam-to-column connection

2.6.4

θMax

Maximum rotation sustained by the beam-to-column connection over at least 2 cycles during testing

2.6.4

Angle between horizontal and diagonal braces

c

Resistance factor for compression member

Pp

Design bearing load

7.1.1

Ω

Factor of safety for ASD

C2.1

Second-order load amplification factor used in the column check

2.6.4

s

Second-order amplification factor calculated using Wpi as the vertical load.

2.6.4

δx

Minimum rack separation distance from building components

2.6.6

ex, ey, and t

Compressive stresses calculated per AISI

C4.1.2

ρ

redundancy factor for earthquake loading

2.1

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concentrically

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6.4 7.1.1

American National Standard Specification for the Design, Testing and Utilization of Industrial Steel Storage Racks

ANSI MH16.1: 2012(R2019)

NOMENCLATURE Note: Terms designated with † are common with AISI-AISC terms that are coordinated between the standards developers.

Automated Storage and Retrieval Systems - A rack structure in which loading and unloading of the racks is accomplished by a stacker crane, or similar vehicle, without the aid of an on-board operator.

Allowable Strength† - Nominal strength divided by the safety factor. Allowable Strength Design (ASD)† - Method of proportioning structural components such that the allowable strength equals or exceeds the required strength of the component under the action of the ASD load combinations.

Allowable Stress. - Allowable strength divided by the appropriate section property, such as section modulus or cross-sectional area.

Applicable Code† - Code (enforced by the local building department) under which the structure is designed.

ASD Load Combination† - Load combination in the applicable building code intended for allowable strength design (allowable stress design).

Beam – Typically, a horizontal structural member that has the primary function of resisting bending moments.

Beam Locking Device - A pin, bolt, or other mechanism that resists disengagement of the beam connector from the column.

Braced Frame† - An essentially vertical truss system that provides resistance to lateral forces and provides stability for the structural system.

Bracing Towers - A bracing system consisting of two vertical plane bracings parallel to main aisle and joined at each load elevation with plan bracing. One of the vertical braces is located at the front column vertical plane and the second at the rear column vertical plane. Buckling - Limit state of sudden change in the geometry of a structure or any of its elements under a critical loading condition.

Buckling Strength - Nominal strength for buckling or instability limit states. Cantilever Rack - A rack structure comprised primarily of vertical columns, extended bases, horizontal arms projecting from the face of the columns, and down-aisle bracing between columns. There can be shelf beams between arms depending on the product being stored. Cantilever columns may be free-standing or overhead tied.

Cantilever Test - A test designed and conducted to determine the connection momentresisting capacity and the rotational rigidity, F, of a beam-to-column connection. The test set-up employs one column segment and one beam segment connected to one another with a beam-to-column connector, with a load applied downwardly in the plane of the frame at the cantilever end of the beam segment.

Case-Flow Rack - A specialized pallet rack structure in which either the horizontal shelf beams support case-flow lanes or case-flow shelf assemblies are supported by the V12a

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American National Standard Specification for the Design, Testing and Utilization of Industrial Steel Storage Racks

ANSI MH16.1: 2012(R2019)

upright frames. The case-flow lanes or shelves are installed at a slight pitch permitting multiple-depth case or box storage with loading from one service aisle and unloading or picking from another service aisle.

Cladding - Exterior covering of structure. Cold-Formed Steel Structural Member† - Shape manufactured by press-braking blanks sheared from sheets, cut lengths of coils or plates, or by roll forming cold- or hot-rolled coils or sheets; both forming operations being performed at ambient room temperature; that is, without manifest addition of heat, such as would be required for hot forming.

Column - Structural member that has the primary function of resisting axial force. Concrete Crushing - Limit state of compressive failure in concrete having reached the ultimate strain.

Concurrent Forces - Two or more forces acting in conjunction with one another at a single location.

Connection† - Combination of structural elements and joints used to transmit forces between two or more members.

Cross-Aisle – One of the two principal directions of the storage rack, corresponding to the direction perpendicular to the principal handling equipment aisle. referred to as the transverse direction.

This is also

Cyclic Tests - A test designed and conducted to determine the connection’s earthquake loading moment-resisting and inelastic rotational capacity and its rotational stiffness, along with energy-dissipation properties, of beam-to-column connections when those connections are subjected to cyclic loading conditions. The test set-up employs one column segment and two beam segments connected to one another, using two beam-to-column connectors, as a double cantilever. Two parallel loads are applied, in opposing reversing cyclic fashion, in the plane of the frame at the ends of, and normal to, the cantilevered beam elements.

Design Load† - Applied load determined in accordance with either LRFD load combinations or ASD load combinations, whichever is applicable.

Design Strength† - Resistance factor multiplied by the nominal strength, Φ Rn. Design Stress - Design strength divided by the appropriate section property, such as section modulus or cross-sectional area.

Diagonal Bracing - Inclined structural member carrying primarily axial force in a braced frame.

Distortional Buckling - A mode of buckling involving change in cross-sectional shape, excluding local buckling.

Double-Stacking - When a shelf is loaded with loads stacked one on top of another in a pallet position.

Down-Aisle – One of the two principal directions of the storage rack, corresponding to the direction of the principal handling equipment aisle. This is also referred to as the longitudinal direction. V12a

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ANSI MH16.1: 2012(R2019)

Drive-In Rack - A rack structure comprised primarily of vertical upright frames, horizontal support arms, and horizontal load rails typically used for one-wide by multiple-depth storage. This structure includes an 'anchor section' with horizontal beams supporting the load rails. Loading and unloading within a bay must be done from the same aisle. A two-way drive-in rack is a special case where back-to-back rows of drive-in racks are combined into a single entity with a common rear post.

Drive-Through Rack - A rack structure comprised primarily of vertical upright frames, horizontal support arms, and horizontal load rails typically used for one-wide by multiple-depth storage. This structure lacks the 'anchor section' found in drive-in racks; therefore, loading and unloading from can be accomplished from both ends of a bay.

Effective Length - Length of an otherwise identical column with the same strength when analyzed with pinned-end conditions.

Effective Length Factor - Ratio between the effective length and the unbraced length of the member.

Effective Section Modulus - Section modulus reduced to account for buckling of slender compression elements.

Effective Width - Reduced width of a plate or slab with an assumed uniform stress distribution which produces the same effect on the behavior of a structural member as the actual plate or slab width with its non-uniform stress distribution.

Factored Load† - Product of a load factor and the nominal load. Flexural Buckling - Buckling mode in which a compression member deflects laterally without twist or change in cross-sectional shape.

Flexural-Torsional Buckling† - Buckling mode in which a compression member bends and twists simultaneously without change in cross-sectional shape.

Force - Resultant of distribution of stress over a prescribed area. Frame – See Upright Frame Guardrails - Members that are installed on an elevated rack supported platform or pick module walkway whose purpose is to provide fall protection for the occupants of the structure. Guardrails consist of a top rail, an intermediate rail and posts. Gravity Load - Load such as that produced by product, dead and live loads, acting in the downward direction.

Handrail – Smooth, continuous railing that runs up a stairway assembly to provide added balance and safety for the occupants as they walk up or down the stairway assembly.

Kick-Plate (Toeboard) – A vertical plate (angle or barrier) that is installed at the edge of an elevated floor that is intended to prevent loose items from sliding off the edge of the floor.

Load Factor† - Factor that accounts for deviations of the nominal load from the actual V12a

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American National Standard Specification for the Design, Testing and Utilization of Industrial Steel Storage Racks

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Load and Resistance Factor Design (LRFD)† - Method of proportioning structural components such that the design strength equals or exceeds the required strength of the component under the action of the LRFD load combinations.

Local Buckling - Limit state of buckling of a compression element within a cross-section. LRFD Load Combination† - Load combination in the applicable building code intended for strength design (load and resistance factor design).

Movable-Shelf Rack - A rack structure comprised primarily of vertical upright frames and horizontal shelf beams and typically used for one-deep pallet or hand-stack storage. Typically, the locations of a couple of shelf levels are 'fixed' with the location of the in-fill shelves being flexible.

Net Area - Gross area reduced to account for removed material. Nominal Strength† - Strength of a structure or component (without the resistance factor or safety factor applied) to resist load effects, as determined in accordance with this Specification.

Out-Of-Plumb Ratio - Maximum horizontal distance (inches or mm) from the centerline of the column at the floor to a plumb line that extends downward from the centerline of the column at the top shelf elevation divided by the vertical distance (feet or m) from the floor to the top shelf elevation.

Out-Of-Straight Ratio – Maximum horizontal distance (inches or mm) from the centerline at any point on the column to a plumb line from any other point on the column divided by the vertical distance (feet or m) between the two points.

Overturning Moment - An applied force that causes a structure to turn over. Pallet Beam - The front and back shelf members that bear the weight of the load and transfer the load to the upright frames.

Pallet-Flow Rack - A specialized pallet rack structure in which the horizontal shelf beams support pallet-flow lanes. The pallet-flow lanes are typically installed on a slight pitch permitting multiple-depth pallet storage with loading from one service aisle and unloading from another service aisle.

Pallet-Load Support Member - Any load bearing member with the long axis on the horizontal plane and intended for use as support of unit loads in direct contact. (pallet and shelf supports and beams, not bracing).

Pallet Rack - A rack structure comprised primarily of vertical upright frames and horizontal shelf beams and typically used for one and two-deep pallet storage.

Pallet Support – A member that extends between the shelf beams at a given level underneath the stored load that aids in the support of that load. Pick Modules - A rack structure comprised primarily of vertical frames and horizontal beams, typically having one or more platform levels of selective, case-flow, or palletflow bays feeding into a central pick aisle(s) [work platform(s)] supported by the rack structure.

Plan and Back Bracing - A bracing system including bracing parallel to the main aisle of the rack located at the back of the rack row and horizontal bracing from the aisle column to the rear braced points. V12a

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American National Standard Specification for the Design, Testing and Utilization of Industrial Steel Storage Racks

ANSI MH16.1: 2012(R2019)

Plaque – Signage permanently and prominently displayed depicting the permissible loading of the rack. Portable Rack (Stacking Frames) - An assembly, typically with four corner columns, that permits stacking of one assembly on top of another without applying any additional load to the product being stored on each assembly.

Portal Test - A test designed and conducted to determine the connection moment-resisting capacity and the rotational rigidity, F, of a beam-to-column connection. The test setup employs two column segments and one beam segment connected to one another using two beam-to-column connectors forming a portal frame, with the load applied laterally in the plane of, and to the corner of, the portal frame in the direction parallel to the beam segment.

Product Load - The weight of the item(s) placed on the rack. Push-Back Rack - A specialized pallet rack structure in which the horizontal shelf beams support push-back lanes comprised of tracks and carts. The push-back lanes are installed on a slight pitch permitting multiple-depth pallet storage. Loading and unloading are done from the same service aisle by pushing the pallets back.

Rack-Supported Platforms - A decked working surface supported by the rack structure. Rack-Supported Structure - A rack structure similar to other rack structures; however, this structure also includes wall girts and roof purlins or equivalent components used to support wall and roof cladding. This structure is designed to withstand wind and snow or rain loads in addition to the normal storage rack loads.

Redundancy Factor – Factor that accounts for the potential of structural distress when the system has lost the carrying capacity of one seismic load carrying element.

Resistance Factor† - Factor that accounts for unavoidable deviations of the nominal strength from the actual strength and for the manner and consequences of failure.

Risk Category – Classification of structures based on the nature of their use. Safety Factor† - Factor that accounts for deviations of the actual strength from the nominal strength, deviations of the actual load from the nominal load, uncertainties in the analysis that transforms the load into a load effect, and for the manner and consequences of failure. The nominal load divided by the safety factor results in the allowable load for an Allowable Strength Design.

Safety Flooring - A surface that is provided in areas where order picking personnel may need to step off the normal walking area or pick module walkway to dislodge loads that may not have properly flowed to their correct position. Seismic Design Category – A classification assigned to a structure based on its Risk Category and the severity of the design earthquake ground motion at the site.

Seismic Response Modification Coefficient - Factor that reduces seismic load effects to strength level.

Sidesway Buckling - Buckling mode where there is translation of the top of the column with respect to the bottom of the column. This mode is also referred to as story buckling and is a buckling mode for the unbraced direction of a pallet rack row. V12a

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ANSI MH16.1: 2012(R2019)

Simple Lip – Single plate elements used to stiffen a compression flange. Site Class Definition - A classification assigned to a location based on the types of soils present.

Stability - Condition reached in the loading of a structural component, frame or structure in which a slight disturbance in the loads or geometry does not produce large displacements.

Stacking Rack – See Portable rack Stacker Rack - A rack structure similar to one of the other rack structures that is serviced by an automated storage and retrieval machine.

Stiffness - Resistance to deformation of a member or structure, measured by the ratio of the applied force (or moment) to the corresponding displacement (or rotation).

Stress - Force per unit area caused by axial force, moment, shear, or torsion. Structural System - An assemblage of load-carrying components that are joined together to provide interaction or interdependence.

Stub-Column Test – Concentric compression testing of members, not affected by column buckling, used to determine the column effectiveness.

Torsional Buckling - Buckling mode in which a compression member twists about its shear center axis.

Torsional-Flexural Buckling. - Buckling mode in which compression members bend and twist simultaneously without change in cross sectional shape.

Trussed-Braced Upright Frame – Upright frames having two columns similar to the chords of a truss and diagonal and horizontal bracing attached to and located between the columns. The diagonals and horizontals become the web members of the truss. (It is referred to as a vertical truss.)

Unbraced Length - Distance between braced points of a member, measured between the centers of gravity of the bracing members.

Unit-Load - The total weight expected to be positioned in the rack consisting of the product load and pallet weight.

Upright Frame – A structural assembly that transfers the vertical and horizontal loads to the floor. It is usually made up of two columns and bracing members between the columns. The beams of the rack are attached to the columns of the frames and transfer the loads to the columns. Vertical Impact Load - Additional downward force added to the beams produced during loading of the rack.

Welded-Wire Rack Deck – A decking system used on pallet rack shelves. Wire decking is fabricated from welded-wire mesh and generally has reinforcements in the form of channels or support wires. Its purpose is to provide additional support for stored material, as well as, becoming a safety net for unstable loads.

Yield Point† - First stress in a material at which an increase in strain occurs without an increase in stress as defined by ASTM. V12a

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American National Standard Specification for the Design, Testing and Utilization of Industrial Steel Storage Racks

ANSI MH16.1: 2012(R2019)

Yield Strength† - Stress at which a material exhibits a specified limiting deviation from the proportionality of stress to strain as defined by ASTM.

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American National Standard ANSI MH16.1: 2012(R2019) Specification for the Design, Testing and Utilization of Industrial Steel Storage Racks

SPECIFICATION FOR THE DESIGN, TESTING AND UTILIZATION OF INDUSTRIAL STEEL STORAGE RACKS 1. GENERAL 1.1 SCOPE This Specification and companion Commentary (hereinafter referred to as the Specification) applies to industrial steel storage racks, movable-shelf racks, racksupported systems and automated storage and retrieval systems (stacker racks) made of cold-formed or hot-rolled steel structural members. Such rack types also include push-back rack, pallet-flow rack, case-flow rack, pick modules, and racksupported platforms. This Specification is intended to be applied to the design of the storage rack portion of any rack structure that acts as support for the exterior walls and roof, except as noted. It does not apply to other types of racks, such as drive-in or drive-through racks, cantilever racks, portable racks, or to racks made of material other than steel.

1.2 MATERIALS This Specification assumes the use of steel of structural quality as defined by the specifications of the American Society for Testing and Materials (ASTM) that are listed in the American Iron and Steel Institute (AISI) North American Specification for the Design of Cold-Formed Steel Structural Members [1]1, and the American Institute of Steel Construction (AISC) Specification for Structural Steel Buildings [2]. Steels not listed in the above specifications are not excluded provided they (a) conform to the chemical and mechanical requirements of either reference [1] or [2] or other published specifications, which establish their properties and structural suitability and (b) are subjected either by the producer or the purchaser to analyses, tests, and other controls in the manner prescribed by either reference [1] or [2] as applicable.

1.3 APPLICABLE DESIGN SPECIFICATIONS Except as modified or supplemented in this Specification, the AISI [1] shall be used for the design of cold-formed members and the AISC [2] shall be used for the design of hot-rolled members. These specifications shall be used to determine the available strength and stiffness of industrial steel storage racks.

1.4 INTEGRITY OF RACK INSTALLATIONS 1.4.1

Owner Maintenance The owner shall maintain the structural integrity of the installed rack system by assuring proper operational, housekeeping, and maintenance procedures including, but not limited to, the following:

1

Numbers in brackets refer to corresponding numbers in Section 10, References to the Text. V12a

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American National Standard ANSI MH16.1: 2012(R2019) Specification for the Design, Testing and Utilization of Industrial Steel Storage Racks

(1) Prohibit any overloading of any pallet positions and of the overall rack system. (2) Regularly inspect for damage. If damage is found, immediately isolate the affected area. Have a storage rack design professional evaluate the damage, and unload, replace or repair if directed by the professional, any damaged columns, beams, or other structural components to restore the system to at least its original design capacity. (3) Require all pallets to be maintained in good, safe, operating condition. (4) Ensure that pallets are properly placed onto pallet load support members in a properly stacked and stable position. (5) Require that all goods stored on each pallet be properly stacked and stable. (6) Prohibit double-stacking of any pallet position, including the top-most position, unless the rack system is specifically designed for such loading. (7) Ensure that the racks are not modified or rearranged in a manner not within the original design configurations per 1.4.4 or as might invalidate the plaque information per 1.4.2.

1.4.2

Plaque The owner is responsible for displaying in one or more conspicuous locations a permanent plaque(s). Each plaque shall have an area of not less than 50 square inches. Plaques shall show in clear, legible print (a) the maximum permissible unit load and/or maximum uniformly distributed load per level, (b) the average unit load (PAverage, see Section 2.6.2) if applicable and (c) maximum total load per bay. The unit load is usually a single pallet or container and its contents that is mechanically transported. Storage levels having multiple stacking of unit loads shall be so identified. It is the responsibility of the owner to ensure that the rack system is not altered in a manner that the plaque information is invalidated.

1.4.3

Conformance All rack installations produced in conformity with this Specification shall be so identified by a plaque having the same characteristics as specified in Section 1.4.2. The same plaque may be used to show permissible unit loads.

1.4.4

Load Application and Rack Configuration Drawings Load application and rack configuration drawings shall be furnished with each rack installation. A copy should be retained by the owner for future reference.

1.4.5

Multiple Configurations If a pallet rack or stacker rack system is designed for more than one shelf configuration or profile, the drawings (Section 1.4.4) are to include either (a) all the permissible configurations or (b) limitations as to the maximum number of shelves, the maximum distance between shelves and the maximum distance from the floor to the bottom shelf. This information is best furnished in table form on the drawings. A notice is to be included in conspicuous text on the drawings stating that deviations from the limitations must be evaluated by a storage rack design professional or the deviation may impair the safety of the rack installation.

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American National Standard ANSI MH16.1: 2012(R2019) Specification for the Design, Testing and Utilization of Industrial Steel Storage Racks

If a change is approved, it shall be added as a permissible configuration on the drawings.

1.4.6

Movable-Shelf Rack Stability The stability of movable-shelf racks is not to depend on the presence, absence or location of the movable shelves. Those components which do provide stability, such as the permanently bolted or welded top shelves and the longitudinal and transverse diagonal bracing, are to be clearly indicated on the rack drawings (Section 1.4.4). For specific movable-shelf rack installations in which the overall rack height is a controlling element, a conspicuous warning is to be placed in the owner’s utilization instruction manual stating any restrictions to shelf placement or shelf removal. Such restrictions are to be permanently posted in locations clearly visible to forklift operators.

1.4.7

Column Base Plates and Anchors The bottom of all columns shall be furnished with column base plates, as specified in Section 7.1. All rack columns shall be anchored to the floor with anchor bolts, which shall be designed in accordance with Section 7.3, to resist all applicable forces as described in Section 2.1 or Section 2.2.

1.4.8

Small Installations For installations not exceeding 12 feet (3.65 m) in height to the top shelf, covering a floor area less than 3,000 square feet (278.7 m2) (not including aisles), having a unit load not exceeding 2,500 pounds (1134 kg), and having no multiple stacking on the top shelf, the provisions given in Sections 1.4.4 and 1.4.5 may be waived.

1.4.9

Rack Damage Preventing damage to rack is beyond the scope of this Specification. See the Commentary for a broader discussion of this topic. Upon any visible damage, the pertinent portions of the rack shall be immediately isolated by the user until the damaged portion is evaluated by a storage rack design professional. Before allowing the rack to be placed back into service the design professional must certify that the rack system and/or the repaired components have been restored to at least their original design capacity.

1.4.10 Racks Connected to the Building Structure If the racks are connected to the building structure, then the location and magnitude of the maximum possible horizontal and vertical forces (per Sections 2.1 and 2.2 of this Specification), that are imposed by the rack to the building, are to be given to the owner of the building for his review.

1.4.11 Out-of-plumb and Out-of-straight Limits 1.4.11.1

Out-of-plumb Limit

The maximum top-to-bottom out-of-plumb ratio for a loaded rack column is 1/240 (for example 1/2 inches per 10 feet (12.5 mm per 3 m) of height). V12a

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American National Standard ANSI MH16.1: 2012(R2019) Specification for the Design, Testing and Utilization of Industrial Steel Storage Racks

Columns whose out-of-plumb ratio exceeds this limit should be unloaded and replumbed. Any damaged parts must be repaired or replaced.

1.4.11.2

Out-of-straight Limit

The maximum out-of-straight ratio for a loaded rack column is 1/240 (0.05 inches per foot or 1/2 inches per 10 feet (12.5 mm per 3 m) of height). Columns whose out-of-straight ratio exceeds this limit should be unloaded and replumbed. Any damaged parts must be repaired or replaced.

2. Loading Rack structures shall be designed using the provisions for Load and Resistance Factor Design (LRFD) or the provisions for Allowable Strength Design (ASD). Both methods are equally acceptable, although they may not produce identical designs.

2.1 LOAD COMBINATIONS FOR THE ASD DESIGN METHOD When the ASD design method is used, all load combinations shall be as stated in the ASCE 7 [4] as modified below for racks. For all rack members 1. 2. 3. 4. 5. 6. 7. 8. 9.

Critical Limit State

D+P Dead Load D+P+L Gravity Load D + P + (Lr or S or R) Snow/Rain Load D + 0.75(P + L + (Lr or S or R)) Gravity + Snow/Rain Load (1 + 0.105SDS)D + 0.75[(1.4 + 0.14SDS)βP + L + (Lr or S or R) + 0.7ρE] Gravity + Seismic (1 + 0.14SDS)D +(0.85 + 0.14SDS)βP + 0.7ρE Gravity + Seismic D + 0.75(P + L + (Lr or S or R) + 0.6W) Gravity + Wind 0.6D + 0.6Papp + 0.6W Wind Uplift (0.6 - 0.14SDS)D + (0.6 – 0.14SDS)βPapp+0.7ρE Seismic Uplift

For load support beams and their connections only: 10. D + L+ 0.5(S or R) + 0.88P + I

Shelf + Impact

where: D= L=

Dead load Live load other than the pallets or products stored on the racks. (Example: floor loading from rack supported platforms) Lr = Roof live load as determined in accordance with ASCE 7 [4] Section 4.9 S= Snow load as determined in accordance with ASCE 7 [4] Chapter 7 R= Rain load as determined in accordance with ASCE 7 [4] Chapter 8 W = Wind load E= Earthquake load I= Impact loading on a shelf (Section 2.3) P= Maximum load from pallets or products stored on the racks. Papp = for seismic uplift, the portion of pallet or product load that is used to compute the seismic base shear. for uplift due to wind, only pallet loads that must be present to develop the lateral wind forces shall be considered in Papp. Papp V12a

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American National Standard ANSI MH16.1: 2012(R2019) Specification for the Design, Testing and Utilization of Industrial Steel Storage Racks

will be zero for an unloaded rack that supports exterior cladding. See Commentary. ρ=

Redundancy factor for earthquake loading as specified in Section 2.6.2.1

β=

Seismic Product Load Coefficient:

0.7 except for uplift combinations where β = 1.0. 2.2 LOAD FACTORS AND COMBINATIONS FOR THE LRFD DESIGN METHOD When the LRFD design method is used, all load factors and combinations shall be as stated in the ASCE 7 [4] except as modified below for racks: For all rack members: 1. 2. 3. 4. 5. 6. 7.

Critical Limit State

1.4D + 1.2P 1.2D + 1.4P + 1.6L + 0.5(Lr or S or R) 1.2D + 0.85P + (0.5L or 0.5W) + 1.6(Lr or S or R) 1.2D + 0.85P + 0.5L + 1.0W + 0.5(Lr or S or R) (1.2 + 0.2SDS)D + (1.2 + 0.2SDS)βP + 0.5L + ρE + 0.2S 0.9D + 0.9Papp + 1.0W (0.9 – 0.2SDS)D + (0.9 -0.2SDS)βPapp + ρE

Dead Load Gravity Load Snow/Rain Wind load Seismic Load Wind Uplift Seismic Uplift

For load support beams and their connections only: 8. 1.2D + 1.6L+ 0.5(S or R) + 1.4P + 1.4I

Product/Live/Impact

All load symbols;β , D, L, P, Lr, S, R, W, E and I are as defined in Section 2.1.

Note: For load case 6 (wind uplift), only the pallet loads that must be present to develop the lateral wind forces shall be considered in Papp. Papp will be zero for an unloaded rack that supports exterior cladding. All resistance factors are to be as stated in the AISI [1] or AISC [2].

2.3 VERTICAL IMPACT LOADS Load-supporting beams and arms and connector components used to attach them to the columns are to be designed for an additional vertical impact load equal to 25 per cent of one unit load. This impact load is to be placed in the most unfavorable position when determining maximum load on each component. For beams or arms whose design capacity is determined by testing (Section 9.3), due allowance must be made for the additional impact load. This impact load need not be applied when checking beam deflections (Sections 5.3 and 9.3) or designing upright frames, columns, and other vertical components.

2.4 HORIZONTAL FORCES 2.4.1 Beam-to-column connections, frame bracing members, and frame bracing to column connections are to be designed for the horizontal forces in this section. The amount of horizontal force that a rack must resist varies with the application. The beam-to-column connections and frame bracing members and frame bracing connections must be designed for the most critical of: 1. Earthquake Loads (Section 2.6) V12a

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American National Standard ANSI MH16.1: 2012(R2019) Specification for the Design, Testing and Utilization of Industrial Steel Storage Racks

2. Wind Loads (Section 2.5) 3. For Allowable Strength Design -1.5%D plus 1.5%P at all connections based on maximum loading. For Load and Resistance Factor Design - 1.5% factored D plus 1.5% factored P based on the maximum loading. These horizontal forces include the effect of out-of-plumbness (Section 1.4.11). These forces are to be applied separately, not simultaneously, in each of the two principal directions of the rack. The horizontal forces are to be applied simultaneously with the full vertical live load, product load and dead load. Bending loads at the beam-tocolumn connection shall be checked against the permissible moments (both positive and negative) determined from the Cantilever Test (Section 9.4.1), the Portal Test (Section 9.4.2), and/or the cyclic load tests (Section 9.6). 2.4.2. Stacker racks or racks fully or partially supporting moving equipment shall meet the requirements of Sections 2.4.2.1, 2.4.2.2 and 2.6. 2.4.2.1. The moving equipment manufacturer is responsible for supplying to the rack manufacturer the magnitude, location, and direction of all loads (static and dynamic) transmitted from the moving equipment to the rack structure. 2.4.2.2. Forces described in Section 2.4.2.1 need not be applied concurrently with the loads described in Sections 2.5 and 2.6.

2.5 WIND LOADS Wind forces shall be determined in accordance with ASCE 7 [4]. Racks directly exposed to the wind shall be designed for the wind loads acting both on the rack structure and the loaded pallets. For stability, consideration is to be given to loading conditions which produce large wind forces combined with small stabilizing gravity forces. Forces from Section 2.4.1 caused by out-of-plumb installation shall be assumed to act concurrently with any wind forces. Forces from seismic (Section 2.6) or moving equipment (Section 2.4.2) need not be assumed to act concurrently with wind forces.

2.6 EARTHQUAKE LOADS 2.6.1

General Where customer specifications require or local building codes dictate that provisions be made for earthquake effects and associated lateral forces, customers, or their representatives, shall bring such requirements to the attention of the rack manufacturer. For each such installation, the storage rack shall be designed, manufactured and installed in accordance with such provisions. Storage racks that are more than 8 feet (2.44 m) in height to the top loaded shelf, and are not connected to buildings or other structures, shall be designed to resist seismic forces in compliance with this section.

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American National Standard ANSI MH16.1: 2012(R2019) Specification for the Design, Testing and Utilization of Industrial Steel Storage Racks

Adequate clearance shall be maintained between the storage rack and the building or other structures to avoid damaging contact during an earthquake (See Section 2.6.6). Unless used to store hazardous material, storage racks are to be deemed Risk Category II structures.

2.6.2

Minimum Seismic Forces The storage rack shall be designed for the total minimum lateral force as determined using the following considerations or, alternatively, the seismic design evaluation may be performed using a displacement-based method.

At-Grade Elevation: Storage rack installed at or below grade elevation shall be designed, fabricated, and installed in accordance with the following requirements: The seismic design forces shall not be less than that required by the following equation for the determination of seismic base shear:

V = C s Ip W s where: Cs = the seismic response coefficient determined in Section 2.6.3. Ip = system importance factor: Ip = 1.5 if the system is an essential facility; Ip = 1.5 if the system contains material that would be significantly hazardous if released; Ip = 1.0 for all other structures; For storage rack in areas open to the public, (e.g., in warehouse retail stores), Ip = 1.5. If a displacement-based evaluation of the rack structure is performed in either of the two principal directions of the rack, Ip may be taken as 1.0 in that direction. Ws = (0.67 xPRF xP) + D + 0.25xL where: PRF = Product Load Reduction Factor Seismic Force Direction

PRF

Cross-Aisle

1.0

Down-Aisle

PAverage PMaximum

PAverage

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For warehouse retail stores, open to the general public, PAverage shall be taken as PMaximum. 7

American National Standard ANSI MH16.1: 2012(R2019) Specification for the Design, Testing and Utilization of Industrial Steel Storage Racks

For all other types of warehousing PAverage is the maximum total weight of product expected on all the beam levels in any row divided by the number of beam levels in that row. PMaximum

Maximum weight of product that will be placed on any one beam level in that row.

Above-Grade Elevation: Storage racks installed at elevations above grade shall be designed, fabricated and installed in accordance with the following requirements: Storage racks shall meet the force and displacement requirements required of nonbuilding structures supported by other structures, including the force and displacement effects caused by amplifications of upperstory motions. In no case shall the value of V be taken as less than the value of FP determined in accordance with Section 13.3.1 of ASCE/SEI 7 [4] where RP is taken equal to R and aP is taken equal to 2.5. As above, Ws = (0.67 xPRF xP) + D + 0.25xL

2.6.2.1

Redundancy Factor The Redundancy Factor, ρ, shall be taken as: For Seismic Design Categories A, B, & C, ρ = 1.0 For Seismic Design Categories D, E, & F : for the down-aisle seismic analysis: ρ = 1.3 for all situations except: ρ = 1.0 for an unbraced rack row with a minimum of two bays connected. for a braced rack row, braced by bracing towers – minimum of two bracing towers per row are utilized.

for a rack row braced by plan and back bracing sections – minimum of three vertical bracing systems per row are utilized.

for the cross-aisle seismic analysis: ρ = 1.3 for the cross-aisle seismic analysis when there is only a single seismic force resisting frame where removal of one brace or connection results in more than a 33% reduction in seismic resistance. ρ = 1.0 when two or more seismic force resisting frames adequately tied together, where removal of one brace or connection does not result in more than a 33% reduction in seismic resistance. V12a

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American National Standard ANSI MH16.1: 2012(R2019) Specification for the Design, Testing and Utilization of Industrial Steel Storage Racks

2.6.3

Calculation of Seismic Response Coefficient When the fundamental period of the rack structure is computed, the seismic response coefficient, Cs, shall be determined in accordance with the following equation:

Cs =

S D1 TR

where: SD1 = Design earthquake spectral response acceleration at a 1 second period as described in Section 2.6.3.1. R = Response modification factor: R = 4.0 in the braced direction and R = 6.0 in the unbraced direction. Higher values may be used if substantiated by tests. T = Fundamental period of the rack structure in each direction under consideration established using the structural properties and deformation characteristics of the resisting elements in a properly substantiated analysis. For the unbraced direction (moment frame), the period shall be determined using a connection stiffness, F, not less than the value from Section 9.4.2 or Section 9.6. Alternatively, the seismic response coefficient need not be greater than the following:

Cs =

S DS R

where: R is as defined above SDS = Design earthquake spectral response acceleration at short period, as described in Section 2.6.3.1. The seismic response coefficient, CS, shall not be taken as less than 0.044SDS. In locations for which the 1-second spectral response, S1, is equal to or greater than 0.6g, the value of the seismic response coefficient, Cs shall not be taken as less than:

Cs =

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0.5S1 R

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American National Standard ANSI MH16.1: 2012(R2019) Specification for the Design, Testing and Utilization of Industrial Steel Storage Racks

2.6.3.1

Design Spectral Response Acceleration Parameters Five-percent damped design spectral response acceleration at short periods, SDS, and at a 1-second period, SD1, shall be determined from the following equations: SDS = (2/3) SMS SD1 = (2/3) SM1 where: SMS = The maximum considered earthquake spectral response accelerations for short period as determined in Section 2.6.3.2. SM1 = The maximum considered earthquake spectral response accelerations for 1-second period as determined in Section 2.6.3.2.

2.6.3.2

Site Coefficients and Adjusted Maximum Considered Earthquake Spectral Response Acceleration Parameters The maximum considered earthquake spectral response acceleration for short periods, SMS, and at 1-second periods, SM1, adjusted for site class effects, shall be determined from the following equations: SMS = FaSS SM1 = FvS1 where: Fa = Site coefficient defined in Table 2.6.3.2 (2). If site class is unknown, use site class D. Fv = Site coefficient defined in Table 2.6.3.2 (3). If site class is unknown, use site class D. Ss = The mapped spectral accelerations for 0.2 second (short) period. S1 = The mapped spectral accelerations for a 1-second period. SS and S1 are obtained from Figures 1 through 6 below or from Chapter 21 of ASCE 7-10. A software program and maps may also be accessed to determine the values at http://seismicmaps.org based on zip code or latitude and longitude of the site. Where zip codes are used to determine spectral accelerations, the maximum value of any location within the zip code shall be used.

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American National Standard ANSI MH16.1: 2012(R2019) Specification for the Design, Testing and Utilization of Industrial Steel Storage Racks

Figure 2.6.3-1 Risk-Targeted Maximum Considered Earthquake Ground Motion for Conterminous United States of 0.2 sec Spectral Response Acceleration (5% of Critical Damping), Site Class B V12a

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American National Standard ANSI MH16.1: 2012(R2019) Specification for the Design, Testing and Utilization of Industrial Steel Storage Racks

Figure 1 (Continued)

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American National Standard ANSI MH16.1: 2012(R2019) Specification for the Design, Testing and Utilization of Industrial Steel Storage Racks

Figure 2.6.3-2 Risk-Targeted Maximum Considered Earthquake Ground Motion for Conterminous United States of 1.0 sec Spectral Response Acceleration (5% of Critical Damping), Site Class B V12a

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American National Standard ANSI MH16.1: 2012(R2019) Specification for the Design, Testing and Utilization of Industrial Steel Storage Racks

Figure 2 (Continued)

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American National Standard ANSI MH16.1: 2012(R2019) Specification for the Design, Testing and Utilization of Industrial Steel Storage Racks

Figure 2.6.3-3 Risk-Targeted Maximum Considered Earthquake Ground Motion for Alaska of 0.2 sec Spectral Response Acceleration (5% of Critical Damping), Site Class B

Figure 2.6.3-4 Risk-Targeted Maximum Considered Earthquake Ground Motion for Alaska of 1.0 sec Spectral Response Acceleration (5% of Critical Damping), Site Class B

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American National Standard ANSI MH16.1: 2012(R2019) Specification for the Design, Testing and Utilization of Industrial Steel Storage Racks

Figure 2.6.3-5 Risk-Targeted Maximum Considered Earthquake Ground Motion for Hawaii, Site Class B

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American National Standard ANSI MH16.1: 2012(R2019) Specification for the Design, Testing and Utilization of Industrial Steel Storage Racks

Figure 2.6.3-6 Risk-Targeted Earthquake Ground Motion for Puerto Rico, Culebra, Vieques, St Thomas, St John, St Croix, Guam and Tutuilla, Site Class B

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American National Standard ANSI MH16.1: 2012(R2019) Specification for the Design, Testing and Utilization of Industrial Steel Storage Racks

TABLE 2.6.3.2 (1) SITE CLASS DEFINITIONS

For SI: 1 foot = 304.8 mm, 1 square foot = 0.0929 m2, 1 pound per square foot = 0.0479 kPa. N/A = Not applicable

TABLE 2.6.3.2 (2) VALUES OF SITE COEFFICIENT Fa AS A FUNCTION OF SITE CLASS AND MAPPED SPECTRAL RESPONSE ACCELERATION AT SHORT PERIODS (Ss)a

a. b.

SITE MAPPED SPECTRAL RESPONSE ACCELERATION AT SHORT PERIODS CLASS Ss≤ 0.25 Ss= 0.50 Ss= 0.75 Ss= 1.00 Ss ≥ 1.25 A 0.8 0.8 0.8 0.8 0.8 B 1.0 1.0 1.0 1.0 1.0 C 1.2 1.2 1.1 1.0 1.0 D 1.6 1.4 1.2 1.1 1.0 E 2.5 1.7 1.2 0.9 0.9 F Note b Note b Note b Note b Note b Use straight-line interpolation for intermediate values of mapped spectral response acceleration at short period, Ss. Site-specific geotechnical investigation and dynamic site response analysis shall be performed to determine appropriate values.

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American National Standard ANSI MH16.1: 2012(R2019) Specification for the Design, Testing and Utilization of Industrial Steel Storage Racks

TABLE 2.6.3.2 (3) VALUES OF SITE COEFFICIENT FV AS A FUNCTION OF SITE CLASS AND MAPPED SPECTRAL RESPONSE ACCELERATION AT 1-SECOND PERIOD (S1)a

a. b.

SITE MAPPED SPECTRAL RESPONSE ACCELERATION AT SHORT PERIODS CLASS S1 ≤ 0.1 S1 = 0.2 S1 = 0.3 S1 = 0.4 S1 ≥ 0.5 A 0.8 0.8 0.8 0.8 0.8 B 1.0 1.0 1.0 1.0 1.0 C 1.7 1.6 1.5 1.4 1.3 D 2.4 2.0 1.8 1.6 1.5 E 3.5 3.2 2.8 2.4 2.4 F Note b Note b Note b Note b Note b Use straight-line interpolation for intermediate values of mapped spectral response acceleration at 1-second period, S1. Site-specific geotechnical investigation and dynamic site response analysis shall be performed to determine appropriate values.

2.6.3.3

Seismic Design Category

Structures shall be assigned a Seismic Design Category based upon the controlling SDS or SD1 value as calculated in Section 2.6.3.1. See Tables 2.6.3.3 (1) or 2.6.3.3. (2), respectively. TABLE 2.6.3.3 (1) SEISMIC DESIGN CATEGORY BASED ON SHORT PERIOD RESPONSE ACCELERATION PARAMETER

Value of SDS SDS < 0.167 0.167 ≤ SDS < 0.33 0.33 ≤ SDS < 0.50 0.50 ≤ SDS

Risk Category I or II III IV A A A B B C C C D D D D

TABLE 2.6.3.3 (2) SEISMIC DESIGN CATEGORY BASED ON 1-S PERIOD RESPONSE ACCELERATION PARAMETER

Value of SD1 SD1 < 0.067 0.067 ≤ SD1 < 0.133 0.133 ≤ SD1 < 0.20 0.20 ≤ SD1 V12a

Risk Category I or II III A A B B C C D D 19

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American National Standard ANSI MH16.1: 2012(R2019) Specification for the Design, Testing and Utilization of Industrial Steel Storage Racks

Structures classified as Risk Category I, II or III that are located where the mapped spectral response acceleration parameter at 1-s period, S1 is greater than or equal to 0.75 shall be assigned to Seismic Design Category E. Structures classified as Risk Category IV that are located where the mapped spectral response acceleration parameter at 1-s period, S1, is greater than or equal to 0.75 shall be assigned to Seismic Design Category F. All other structures shall be assigned to a Seismic Design Category based on their Risk Category and the design spectral response acceleration coefficients, SDS and SD1 determined in accordance with Section 2.6.3.1.

2.6.4

Connection Rotational Capacity ӨMax is the maximum rotation sustained by the beam-to-column connection over at least two cycles during testing. The rotational capacity, ӨMax, of the beam-tocolumn connection shall be demonstrated by testing per Section 9.6 to be greater than the rotational demand, ӨD. .

ΘD =

Cd (1+α s ) Δ s h total

where: Cd is the deflection amplification factor (See Section 2.6.6) htotal is the height of the top loaded shelf level αs is the first iteration of the second order amplification term calculated using a properly substantiated analysis such as provided in Section 2.6.4 of the Commentary. Wpi from Section 2.6.4 of the Commentary shall be used to determine the gravity amplification term. Δs is the seismic displacement at the height of the top loaded shelf level. The seismic displacement used for Δs should be 1.5 times the computed displacement if the seismic displacement was computed using the ASD design method.

Alternately, for racks assigned to Seismic Design Category A, B, or C, the rotational connection capacity check need not be made if the seismic response coefficient is taken as:

Cs = 2.6.5

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S DS R

Seismic Displacement The displacement at the top shelf level resulting from the seismic load is Δs . The displacement shall be determined using the same structural system stiffness as used to determine the period for the base shear calculation in Section 2.6.3 and using the base shear from Section 2.6.2, including the Ip factor. 20

American National Standard ANSI MH16.1: 2012(R2019) Specification for the Design, Testing and Utilization of Industrial Steel Storage Racks

The displacement should be calculated using LRFD-level seismic forces. Refer to the commentary for discussion.

2.6.6

Seismic Separation Seismic separation need not be checked in Seismic Design Categories A, B, or C. If an analysis is performed, the minimum separation distance between the rack structure and the building structure, which includes any attached permanent components or elements, shall be equal to the total deflection, δx, determined as follows: δx = (Cd *δxe)/IP where: Cd = deflection amplification factor Direction

Cd 3.5 5.5

Braced direction Unbraced direction

δxe = storage rack deflection calculated by an elastic analysis IP = Importance Factor In lieu of an analysis, rack structures shall be separated from the building structure and any attached permanent components or elements by a distance not less than:

Direction

Braced direction Unbraced direction

Separation 0.02 htotal 0.05 htotal

where: htotal is the height of the top shelf level

2.6.7

Vertical Distribution of Seismic Forces The lateral force, Fx, at any level shall be determined from the following equations: If the centerline of the first shelf level is 12 inches (305 mm) above the floor or less:

F1 = C s I p w1

For the first shelf level

and

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American National Standard ANSI MH16.1: 2012(R2019) Specification for the Design, Testing and Utilization of Industrial Steel Storage Racks

Fx =

(V − F1 )wx hx

For levels above the first level

n

 wi hi

i =2

If the centerline of the first shelf level is greater than 12 inches (305 mm) above the floor:

Fx =

Vw x h x

For all levels

n

w h i =1

i

i

where: V

= total design lateral force or shear at the base of the rack

wi or wx = the portion of the total gravity load on the racks, including live load, dead load and product load, times the product load reduction factor, (Section 2.6.2) that are located or assigned to the designated shelf level, level i or x hi or hx

2.6.8

= the height from the base to level i or x

Horizontal Shear Distribution The seismic design shear at any level, Vx, shall be determined from the following equation: n

Vx =  Fi i= x

where Fi = the portion of the seismic base shear, V, induced at level i. The seismic design shear, Vx, shall be distributed to the various vertical elements of the seismic force resisting system at the level(s) under consideration based on the relative lateral stiffnesses of those elements.

2.6.9

Overturning Safety against overturning moment shall be designed on the basis of the following conditions of Product Load, P: 1. Weight of rack plus every storage level loaded to 67 percent of its rated load capacity 2. Weight of the rack plus the highest storage level only loaded to 100 percent of its rated capacity The design shall consider the actual height of the center of mass of each storage load component.

2.6.10 Concurrent Forces Forces described in Sections 2.4.1 and 2.5 need not be assumed to act concurrently with seismic forces.

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American National Standard ANSI MH16.1: 2012(R2019) Specification for the Design, Testing and Utilization of Industrial Steel Storage Racks

3. DESIGN PROCEDURES All computations for safe loads, stresses, deflections, and the like shall be made in accordance with conventional methods of structural design as specified in the AISI [1] for cold-formed steel components and structural systems and the AISC [2] for hotrolled steel components and structural systems, except as modified or supplemented by this specification. In cases where adequate methods of design calculations are not available, designs shall be based on test results obtained in accordance with this specification or Section F of the AISI [1]. No slenderness limitations shall be imposed on tension members that are not required to resist compression forces under the various load combinations specified in Section 2.1 or 2.2.

4. DESIGN OF STEEL ELEMENTS AND MEMBERS The effect of perforations on the load-carrying capacity of compression members is accounted for by the modification of some of the definitions of the AISI [1] and the AISC [2] as described below.

4.1 COLD-FORMED STEEL MEMBERS 4.1.1

Properties of Sections Exceptions to the provisions of the AISI [1] for computing the section properties are given below in Sections 4.1.2 and 4.1.3. Except as noted, all cross-sectional properties shall be based on full unreduced and unperforated sections considering round corners.

4.1.2

Flexural Members Se = Elastic section modulus of the net section times ( 0.5 +

Q ) for the extreme 2

compression fiber. Sc = Elastic section modulus of the net section for the extreme compression fiber times.

(1 − Q )  Fc  1− 2

Q

F   y

The value of Q shall be determined according to Section 9.2.2. Section properties j, ro, and Cw shall be permitted to be computed assuming sharp corners. Inelastic reserve capacity provisions of the AISI [1] Section C3.1.1 (b) shall not be considered for perforated members.

4.1.3

Concentrically Loaded Compression Members

4.1.3.1

Effective Area

Ae = Effective area at the stress Fn determined according to Section 4.1 when applicable. Where Section 4.1 is not applicable, Ae shall be calculated as: V12a

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American National Standard ANSI MH16.1: 2012(R2019) Specification for the Design, Testing and Utilization of Industrial Steel Storage Racks Q   Fn   A e = 1 − (1 − Q)   Anet min   Fy   

where the Q factor shall be determined by the procedure specified in Section 9.2 and Anet min is defined in Section 9.2. Lx, Ly, and Lt are the unbraced lengths defined in Section 6.3 for bending about x- and y-axes and twisting. The torsional warping constant, CW, may be calculated based on sharp corners.

4.1.3.2

Distortional Buckling

Open sections, except for those with unstiffened elements or only simple lip edge stiffeners, shall be checked for the effects of distortional buckling by testing or rational analysis.

4.2 HOT-ROLLED STEEL COLUMNS All hot-rolled steel columns shall be designed according to Section E, of the AISC [2], except as noted below. The nominal compressive strength Pn shall be calculated as follows:

Pn =Ae Fc Ae is defined in Section 4.1.3.1 The value of Q shall be determined by testing in accordance with Section 9.2.2.

5. BEAM Design 5.1 CALCULATIONS The bending moments, reactions, shear forces, and deflections shall be determined by considering the beams as simply-supported, or by rational analysis for beams having partial end-fixity. Where the shape of the beam cross-section and endconnection details permit, permissible loads for pallet-carrying beams shall be determined by conventional methods of calculation according to the AISI [1] or the AISC [2].

5.2 CROSS SECTION Where the configuration of the cross-section precludes calculation of allowable loads and deflections, the determination shall be made by tests in accordance with Section 9.

5.3 DEFLECTIONS At working load (excluding impact), the deflections shall not exceed 1/180 of the span measured with respect to the ends of the beam.

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American National Standard ANSI MH16.1: 2012(R2019) Specification for the Design, Testing and Utilization of Industrial Steel Storage Racks

5.4 BEAM-TO-COLUMN CONNECTIONS 5.4.1

General Adequate strength (and where required, adequate rotational stiffness and rotational capacity) of connections to withstand the calculated resultant forces, moments and, where required, displacement demands, shall be established by test or, where possible, by calculation. Test procedures for various connections are specified in Section 9.

5.4.2

Beam Locking Device Except for movable-shelf racks, beams subject to machine loading shall have connection locking devices (or bolts) capable of resisting an upward force of 1,000 pounds (453.6 kg) per connection without failure or disengagement.

5.4.3

Movable-Shelf Racks For movable-shelf racks, the top shelf and other fixed shelves are to include support connections capable of resisting an upward force of 1,000 pounds (453.6 kg) per connection without failure or disengagement. The movable shelves are generally constructed of a set of front and rear longitudinal beams connected rigidly to each other by transverse members. The movable shelves are to be connected in such a way so as to prevent forward displacement when lifting out the front beam of the shelf.

5.5 PALLET SUPPORTS Pallet support members extending between the shelf beams at a given level shall be designed for the worst loading condition considering the dimensions of the storage rack, the dimensions and configuration of the bottom of the pallet and the anticipated pallet placement. The warehouse operator must make the rack system designer aware of the expected configuration, condition, and construction of the pallets to be used.

5.6 WELDED-WIRE RACK DECKING Where Welded-Wire Rack Decking is utilized to support the load, it shall be designed in accordance with ANSI MH26.2 [6].

6. UPRIGHT FRAME DESIGN 6.1 DEFINITION The upright frame consists of columns and bracing members.

6.2 GENERAL 6.2.1

Upright frames and multi-tiered portal frames Upright frames and multi-tiered portal frames shall be designed for the critical combinations of vertical and horizontal loads for their most unfavorable positions as specified in Section 2. All moments and forces induced in the columns by the

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American National Standard ANSI MH16.1: 2012(R2019) Specification for the Design, Testing and Utilization of Industrial Steel Storage Racks

beams shall be considered. In lieu of the calculation, frame capacity may be established by tests according to Section 9.5.

6.2.2

Connections Connections that cannot be readily analyzed shall be capable of withstanding the moments and forces in proper combinations as shown by test.

6.3 EFFECTIVE LENGTHS Effective lengths for columns are those specified in Sections 6.3.1 through 6.3.4, or as determined by rational analysis or tests. Guidance for using an effective length method is given in the following subsections. It is not intended to preclude the use of other design methods. Other rational methods, as specified by AISC [2] and AISI [1] may be used. One column stability design method should be used consistently throughout the analysis of one structure.

6.3.1

Flexural Buckling in the Direction Perpendicular to the Upright Frames Lx is the distance from the centerline of one beam to the centerline of the next beam or the distance from the floor to the centerline of the first beam.

6.3.1.1

Racks Not Braced Against Sidesway For the portion of the column between the bottom beam and the floor, as well as between consecutive beam levels, the effective length factor K shall be taken as 1.7, or as otherwise determined by an analysis properly accounting for the stiffness of members, the semi-rigid nature of the beam-to-column connections and the partial fixity of the base, allowing for average load reduction, as applicable. If a K of 1.7 is used without analysis, then no reduction of this value shall be made.

6.3.1.2

Racks Braced Against Sidesway The effective length factor for pallet racks, stacker racks, and movable-shelf racks is K = 1, provided that all such racks have diagonal bracing in the vertical plane and that such racks have either a rigid and fixed top shelf or diagonal bracing in the horizontal plane of the top fixed shelf. Increased column capacity may be achieved by placing an additional rigid and fixed shelf (or shelves) or bracing in the horizontal plane. The unsupported length is defined as the distance from floor to fixed top shelf or bracing; or, in the case of additional rigid fixed shelf (or shelves) or fixed shelf with diagonal bracing in its horizontal plane, the unsupported length is the distance between fixed shelves or braced shelves. The effective length factor is K = 1. If there is no bracing in the vertical plane of the rack, the K values are the same as for racks per Section 6.3.1.1, Racks Not Braced Against Sidesway.

6.3.2

Flexural Buckling in the Plane of the Upright Frame

6.3.2.1 Ly is defined as the distance along the neutral axis of the column between the intersection of the neutral axis of the column with the neutral axis of either two adjacent diagonals or a diagonal and a horizontal. V12a

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American National Standard ANSI MH16.1: 2012(R2019) Specification for the Design, Testing and Utilization of Industrial Steel Storage Racks

6.3.2.2 For upright frames having diagonal braces or a combination of diagonal and horizontal braces that intersect the columns, the effective length factor, K, for the portion of the column between braced points shall be taken as 1.0, provided that the maximum value of the ratio of Lshort to Llong does not exceed 0.15. Lshort or Llong is defined as the distance between the intersection of the neutral axis of the column with the neutral axis of either two adjacent diagonals or a diagonal and a horizontal. In an upright frame with diagonals and horizontals, Lshort and Llong refer to the minimum and maximum distances between two adjacent segments between two adjacent horizontals. In an upright frame with only diagonal Lshort and Llong refer to two adjacent segments. All distances are measured along the neutral axis of the column. 6.3.2.3 For upright frames having diagonal braces that intersect the horizontal braces, the effective length factor K for the portion of the column between braced points shall be taken as 1.0 providing the ratio of Lshort to Llong does not exceed 0.12. Lshort is defined as the shortest distance between the intersection of the neutral axis of one of the two diagonal braces with the neutral axis of the horizontal brace, or the shortest distance between the intersections of one diagonal brace with the neutral axis of the horizontal brace with the neutral axis of the column. Llong is defined as the length of the horizontal brace measured between the neutral axes of the columns. All measurements are along the neutral axis of the horizontal brace. 6.3.2.4 For the upright frames having bracing patterns not included above, the effective length factor K of the column shall be determined by rational analysis or by upright frame testing.

6.3.3

Torsional Buckling

6.3.3.1 Lt is the length of the member unsupported against twisting. 6.3.3.2 The effective length factor, Kt, for torsional buckling shall be taken as 0.8 provided that the connection details between the columns and the braces are such that the twisting of the column is prevented at the brace points. If the connection details do not prevent twist, Kt can be larger and shall be determined by rational analysis or testing. 6.3.4

Diagonals and Horizontals For compression diagonals and horizontal members of trussed upright frames, the effective length is the full unsupported length of the member. The analysis and design of the upright frame joints (or connections) shall include a consideration of the transfer of the member forces into and through those joints along with their connections and the deformation of the member legs, lips, and stiffening elements that make up the cross section of the various members coming into each joint.

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American National Standard ANSI MH16.1: 2012(R2019) Specification for the Design, Testing and Utilization of Industrial Steel Storage Racks

6.4 STABILITY OF TRUSSED-BRACED UPRIGHT FRAMES To prevent trussed-braced upright frames from becoming unstable and buckling in their own plane, the columns of such upright frames shall be designed using the appropriate provisions of the AISI [1] or the AISC [2] for a value KL/r or Kl/r, respectively, equal to:

 2EA Pcr where for Pcr the following apply: 1. For upright frames braced with diagonals and horizontals: Pcr =

 2 EI

1

2 2

k l

 I  1 b    2 2  2 + aA  k l  A d sin cos  b 2

1+

2. For upright frames braced with diagonals only:

Pcr =

 2 EI

1

2 2

k l

1+

 I 2

1

2 2

A d sin cos 2 

k l

3. For upright frames braced with horizontals only, and with fully rigid connections:

Pcr =

 2 EI

1  k l  I ab a2   1 + 2 2  + k l  12 I br 24 I c  2 2

2

where: a A Ab Ad b E I Ibr Ic V12a

Vertical distance between the horizontal brace axis. Sum of the minimum net area (Anet min.) of the columns of the upright frame. Cross-sectional area of a horizontal brace. Cross-sectional area of a diagonal brace. Horizontal distance between neutral axes of the columns. The modulus of elasticity of steel. Minimum net moment of inertia of the columns about the gravity axis of the upright frame perpendicular to the plane of the upright frame Moment of inertia of the horizontal brace about its own axis perpendicular to the plane of the upright frame. Minimum net moment of inertia of one column about its own major axis perpendicular to the plane of the upright frame. 28

American National Standard ANSI MH16.1: 2012(R2019) Specification for the Design, Testing and Utilization of Industrial Steel Storage Racks

k

=1.1 if the center of gravity of the loads along the upright frame is below midheight. =1.6 if the center of gravity is below the upper third-point of the height. =2.0 if the center of gravity is above the upper third-point of the height.

l 

Total height of the upright frame. Angle between horizontal and diagonal braces.

7. COLUMN BASE Design 7.1 COLUMN BASE PLATES 7.1.1

Bearing on concrete Provision shall be made to transfer column forces and moments into the floor. These forces and moments shall be consistent in magnitude and direction with the rack analysis. Unless otherwise specified, the maximum allowable bearing stress F’p (ASD) or design bearing load Pp (LRFD) on the bottom of the plate shall be determined as follows: for ASD: F'p = 0.7f ' c

for LRFD: Pp = 17 . f c' A Effective Base Bearing Area

 = 0.60 where f’c = the minimum 28-day compression strength of the concrete floor which, unless otherwise brought to the attention of the rack manufacturer, shall be assumed to be 3,000 psi (2.1 x 106 kg/m2).

7.1.2

Base plate design Once the required bearing area has been determined based on the allowable bearing stress, F’p, the minimum thickness of the base plate is determined by rational analysis or by appropriate test using a test load 1.5 times the ASD design load or the factored LRFD load. Upon request, information shall be given to the owner or the owner’s agent on the location, size, and pressures under the column base plates for each type of upright frame in the installation. When rational analysis is used to determine base plate thickness, the base plate shall be designed for the following loading conditions, where applicable.

7.1.2.1

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Downward vertical force The effective area of the base plate is defined as the minimum area needed to satisfy the concrete bearing requirements or the minimum bearing area required by the concrete slab designer. This area may be the area bounded by the perimeter of the rack column, the full area of the base plate, or some area in between these two values. The resulting area is defined as the effective base 29

American National Standard ANSI MH16.1: 2012(R2019) Specification for the Design, Testing and Utilization of Industrial Steel Storage Racks

plate area. The base plate thickness shall be calculated assuming that the bearing pressure is uniformly distributed over the effective base plate area and the plate shall be analyzed as a rigid member.

7.1.2.2

Uplift/tension force When the base plate configuration uses a single anchor bolt and a net uplift force exists, the minimum base plate thickness shall be determined based on a design bending moment in the plate equal to the uplift force times 1/2 the distance from the centerline of the anchor to the nearest edge of the rack column. When the base plate configuration consists of two anchor bolts located on either side of the column and a net uplift force exists, the minimum base plate thickness shall be determined based on a design bending moment in the plate equal to the uplift force on one anchor times 1/2 the distance from the centerline of the anchor to the nearest edge of the rack column.

7.1.2.3

Axial load plus bending (down-aisle seismic or wind) When downward axial loads and bending moments due to lateral loads exist, the base plate thickness and anchor forces shall be determined as follows: When e = M/P <= N/6, where N = effective length of the base plate in the downaisle direction, no uplift of the base plate will occur. Therefore, no tension force will be present in the anchors and the anchors shall be designed for the maximum calculated shear force. The base plate thickness shall be determined per Section 7.1.2.1. When e > N/6, where N = effective length of the base plate in the down-aisle direction, then a tension force may occur in the anchor(s). The tension force can be calculated directly once the compressive stress block underneath the plate has been established. In order to calculate the anchor tension, the designer must assume either the peak magnitude of the stress distribution or the length of the stress block. Once the concrete stress block distribution and magnitude has been established, the anchor tension can be calculated directly through the equations of equilibrium. The base plate thickness shall be determined per Section 7.2.2.1.

7.1.3

Maximum Considered Earthquake Base Rotation Where base bending moments are assumed in the design the base shall have a rotational capacity, Өb, of not less than

Θb =

Cd (1+αS ) Mb Kb

Where: Cd is the deflection amplification factor per Section 2.6.6. αs is the first iteration of the second order amplification term computed using Wpi from Section 2.6.4 of the Commentary. Mb is the base moment from analysis. The moment used for Mb should be 1.5 times the computed base moment if the base moment was computed using the ASD design method. V12a

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American National Standard ANSI MH16.1: 2012(R2019) Specification for the Design, Testing and Utilization of Industrial Steel Storage Racks

Kb is the base rotational stiffness used in the structural analysis that determined Mb. If the rotational capacity of the base is exceeded, the structural components must be modified until the base rotational demand equation above is satisfied.

7.1.4

Shims Shims may be used under the base plate to maintain the plumbness and/or levelness of the storage rack. The shims shall be made of a material that meets or exceeds the design bearing strength (LRFD) or allowable bearing strength (ASD) of the floor. The shim size and location under the base plate shall be equal to or greater than the required base plate size and location. In no case shall the total thickness of a shim stack under a base plate exceed six times the diameter of the largest anchor bolt used in that base. Shims stacks having a total thickness greater than two and less than or equal to six times the anchor bolt diameter under bases with only one anchor bolt shall be interlocked or welded together in a fashion that is capable of transferring all the shear forces at the base. Shims stacks having a total thickness of less than or equal to two times the anchor bolt diameter need not be interlocked or welded together. Bending in the anchor associated with shims or grout under the base plate shall be taken into account in the design of anchor bolts.

7.2 SLAB AND SUBGRADE EVALUATION The owner is responsible for retaining a qualified engineer to evaluate the slab and the subgrade to make sure they will adequately support all storage rack loads. It is the responsibility of the rack supplier to provide the column loading and base detail information that is needed for the evaluation.

7.3 ANCHOR BOLTS 7.3.1

Anchor Bolt Design The anchor bolt design shall be in accordance with the provisions of ACI 318 Appendix D. The redundancy factor in the load combinations in Section 2.1 and 2.2 shall be 1.0.

7.3.2

Periodic Inspection of Anchor Bolt Installation When periodic inspection of the anchor bolt installation is required, the owner, or the owner’s designated representative, shall retain a qualified inspector to conduct the inspection. Only the anchors in the main force-resisting system need to be inspected. See the commentary for a broader discussion of this topic.

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American National Standard ANSI MH16.1: 2012(R2019) Specification for the Design, Testing and Utilization of Industrial Steel Storage Racks

8. SPECIAL RACK DESIGN PROVISIONS 8.1 OVERTURNING Overturning is to be considered for the most unfavorable combination of vertical and horizontal loads. Stabilizing forces provided by the anchor bolt are not considered in checking overturning, unless the anchors and floor are specifically designed and installed to meet these uplift forces (Sections 2.5 and 2.6). Unless all columns are so anchored, the ratio of the restoring moment to overturning moment shall not be less than 1.5. The height-to-depth ratio of a storage rack shall not exceed 6 to 1 measured to the top loaded shelf level, unless the rack is anchored or braced externally to resist all forces. The height is measured from the floor to the top loaded shelf level and the depth from face to face of the upright column. Storage rack, which is loaded and unloaded by powered handling equipment, that exceeds the 6 to 1 ratio defined above, shall also be designed to resist a 350 pound (159 kg) side force applied to any single frame at the top loaded shelf level in a direction perpendicular to the aisle. For LRFD design method, the load factor applied to this force shall be 1.6. This force is to be applied to an empty frame and divided into as many frames as are interconnected in the direction of the force. Anchors and base plates will be designed to resist uplift forces from this force when applied to an empty frame. Frame columns need not be designed for the additional axial load from this force. Unless it can be shown to be unnecessary because of such factors as soil, slab and frame stiffness, single rows of rack exceeding a height-to-depth ratio of 8 to 1 must be tied externally to the building or cross-aisle to another rack. Stabilizing a single rack with a height-to-depth ratio over 8 to 1 with anchoring alone is not recommended, unless designed and certified by an engineer. The 350 pound (159 kg) side force in this section need not be applied concurrently with the horizontal forces of Sections 2.4, 2.5 or 2.6.

8.2 CONNECTIONS TO BUILDINGS Connections of racks to buildings, if any, shall be designed and installed to prevent reactions or displacements of the buildings from damaging the racks or the reactions or displacements of the racks from damaging the building (see also Section 1.4.10).

8.3 INTERACTION WITH BUILDINGS Storage rack located at levels above the ground level (as described in Section 2.6.2), rack buildings, or racks which depend upon attachments to buildings or other structures at other than floor level for their lateral stability, shall be designed to resist seismic forces that consider the responses of the building and storage rack to seismic ground motion and their interaction so as not to cause damage to one another.

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American National Standard ANSI MH16.1: 2012(R2019) Specification for the Design, Testing and Utilization of Industrial Steel Storage Racks

8.4 PICK MODULES AND RACK SUPPORTED PLATFORMS Pick modules and rack supported platforms that are used by authorized or trained personnel, and are not open to the general public, shall be designed in accordance with this section.

8.4.1

Posting of Design Loads The design loads for the floor areas of the rack supported platforms and pick module walkways shall be shown on the rack configuration and load application drawings. These design loads shall also be displayed in one or more conspicuous locations within the structure, such as at the top of the access stairway.

8.4.2

Design Requirements Rack supported platforms and pick module walkways shall be designed for the maximum concentrated loads and the maximum uniformly distributed loads that are to be imposed on the rack supported platform floor. The owner or owner’s agent shall advise the designer of the rack supported platform or pick module of all loads that are expected on the structure for its present or future use. The design load for the foot traffic on pick module walkways shall be at least 60 psf (293 kg/m2) live load superimposed over the entire area of the foot traffic walkway. Where applicable the pick module floor shall also be designed for conveyor leg loading, pallet staging, shelving, mobile-handling equipment or any other items that could cause additional load on the pick module walkway. In some cases, conditions may require a higher design load. The user should advise the designer of all such conditions. The pick module walkway shall also be designed for other items, such as lights or sprinkler pipes, that may be hung from the pick module walkway floor or floor supports. If the project specifications dictate that a pick module walkway live load greater than or equal to 100 psf (488 kg/m2) is required and there are two or more elevated floor levels, the live load may be reduced by 20 percent for the design of the column framing system which includes the support columns, the frame bracing, the frame bracing connections and the base plates. This reduction does not apply to the beams that support the floor or their connections. The maximum live load deflection for beams that support rack supported platforms shall not be greater than L/240. The total load deflection shall not be more than L/180. The clear width of a pick module walkway shall be at least 30 inches (760 mm).

8.4.3

Rack Supported Platform and Pick Module Walkways Guardrails - Members that are installed on an elevated rack supported platform or pick module walkway whose purpose is to provide fall protection for the occupants of the structure. Guardrails consist of a top rail, an intermediate rail and posts.

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Safety Flooring – A surface that is provided in areas where order picking personnel may need to step off the normal walking area or pick module walkway to dislodge loads that may not have properly flowed to their correct discharging positions. 33

American National Standard ANSI MH16.1: 2012(R2019) Specification for the Design, Testing and Utilization of Industrial Steel Storage Racks

Kick-plate – Kick-plates are vertical plates that extend upward at the edge of a floor surface to prevent loose items from sliding off the edge of the floor.

8.4.3.1

Guardrail Requirements The horizontal top rail of the guardrail shall be 42 inches (1067 mm) above the walking surface. Guardrails shall have a top rail and intermediate members such that a 21 inch (533 mm) sphere cannot pass through below the top rail level. The ends of the rails shall not extend beyond the post, except where extending the rails will not create a hazard. Where there is a discontinuity of the guardrail that exceeds 6 inches (152 mm), such as between vertical members or between stairs and a vertical member, filler guardrail is required to provide fall protection for this space. The top and intermediate guard rails or any other part of the guardrail assembly must be designed to resist the following loads applied separately (not simultaneously): 1. Concentrated live load of 200 pounds (91 kg) applied at any location along the top rail assembly in any direction. 2. Distributed live load of 20 plf (40 kg/m) applied in any direction along the length of any member that is part of the assembly. Guardrails are not required to be in place where they would interfere with product being loaded into or removed from the pick module system. Guardrail must be provided to close any other openings through which an order picker may fall. Where guardrails are omitted for pallet drops, safety gates, removable guardrail sections or removable chains must be used for fall protection. These devices must meet the same strength and configuration requirements as the permanently installed guardrail.

8.4.3.2

Safety Flooring Requirements Safety flooring shall be designed for a 300 pound (136 kg) concentrated load (to support the picker) and a distributed live load of 60 psf (293 kg/m2) acting separately. The pickers shall not walk out onto the safety flooring without observing the correct safety procedures that are required for the pick module use. The pickers shall stay at least 4 feet away from the open end of the safety flooring.

8.4.3.3

Kick-plate Requirements Kick-plates shall extend at least 4 inches (102 mm) above the floor surface. Kick-plates are not required at picking locations but are required at pallet drop locations. The user shall specify to the designer any additional areas where kick-plate may be needed for safety due to the configuration of the pick module.

8.4.3.4

Special Conditions Floor openings under the conveyor path that are used for the discharge of trash need not have guardrail or kick plates as this would interfere with the efficient discharge of trash. Where conveyor inclines rise through an opening in the floor, guardrail is generally required on all sides, except the side where use of such guardrail would interfere with the conveyor or product.

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American National Standard ANSI MH16.1: 2012(R2019) Specification for the Design, Testing and Utilization of Industrial Steel Storage Racks

Toe-plates are not required where rack frame bracing or other structural components such as shelf decking or safety flooring are next to the edge of the floor. Guardrails are not required at locations where other structural members such as rack frame horizontal members are provided that meet the strength and configuration requirements of the guardrail.

8.4.4

Stairways Fixed stairways shall be provided for access to elevated rack supported platforms or pick modules by authorized or trained personnel. Fixed stairways shall be designed and constructed to carry a load of 100 psf (488 kg/m2) but shall not be of less strength than to carry a concentrated live load of 300 pounds (136 kg) at any point along the stairway. (Other requirements may need to be considered.) Fixed stairways shall have a minimum tread width of 30 inches (762 mm). A vertical clearance of 7 feet (2.1 m) shall be maintained between the stairway and any overhead obstruction measured from the leading edge of the tread. Stairways shall be installed at angles to the horizontal of between 30 and 50 degrees. The sum of the rise and the run of a single step should be approximately 17.5 inches (445 mm) with the minimum rise of 6.5 inches (165 mm) and a maximum rise of 9.5 inches (241 mm). Rise height and tread length shall be uniform throughout any flight of stairs including any foundation structure used as one or more of the treads of the stairs. Open risers are allowed. Stairway landings shall be no less than the width of the stairway and a minimum of 30 inches (762 mm) in length measured in the direction of travel. Intermediate landings are required if vertical rise exceeds 12 feet (3.66 m). Handrails shall be provided on both sides of all stairways. If the total rise of the stairway is less than 44 inches (1118 mm) stair handrails are not required. Stair Handrail – Smooth, continuous railing that runs up a stair rise assembly to provide added balance and safety for the occupants as they walk up or down the stair rise assembly. Stair handrail shall be 30 inches (762 mm) to 34 inches (864 mm) in height when measured from the top of each tread at the face of the tread. Stair handrail brackets or posts supports shall be spaced at no more than 8 feet (2.44 m) centers and the rail shall be mounted so a clearance of at least 3 inches (76 mm) exists horizontally between the rail and any obstruction. Stair handrails shall be designed for the same forces as guardrails. Stair handrail extensions are not required in pick module or rack supported platform stair assemblies.

8.4.5

Product Fall Protection The owner should specify to the designer any locations where operations may require horizontal or vertical safety barriers. These barriers shall prevent product from falling into those areas.

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American National Standard ANSI MH16.1: 2012(R2019) Specification for the Design, Testing and Utilization of Industrial Steel Storage Racks

8.5 AUTOMATED RACKS)

STORAGE

AND

RETRIEVAL

SYSTEMS

(STACKER

Stacker racks may be “Load Arm and Rail Type” or “Beam Column Type” and can be used in “Rack Supported Systems”. Shown in parenthesis in the heading are the numbers corresponding to parts of this Specification.

8.5.1

Tolerances (1.4.11) Installation and design tolerances shall be supplied by the user of the installation based on the requirements of the equipment manufacturer.

8.5.2

Vertical Impact Loads (2.3) The moving equipment manufacturer is responsible for supplying to the rack manufacturer information on maximum vertical static and dynamic loads for the design of racks; the rack structures shall be designed for these loads.

8.5.3

Horizontal Loads (2.4) Horizontal loads specified in Sections 2.4.1 and 2.4.2 of the Specification shall be used in the design of racks.

8.5.4

Wind (2.5) and Snow Loads (2.1) Wind (including uplift) and snow loads shall be considered in the design of rack during erection and use. In determining the total force on a rack structure, forces in all members of the structure shall be accounted for with proper consideration of shielding effects, the shape effect, and other applicable forces. The forces specified in Sections 2.4.1, 2.4.2 and 2.6 do not act concurrently with wind loads.

8.5.5

Deflections (5.3) Deflections shall not exceed the limits set by the requirements of the equipment operation.

8.5.6

Rack Compatibility with the Equipment Horizontal and vertical deflections shall be calculated and reviewed with the crane equipment supplier for compatibility. Rack design shall be compatible with the equipment. The basic considerations shall include the height of the first shelf, clearance from the top shelf to the crossaisle tie, shuttle window height, and sprinkler system.

9. TEST METHODS 9.1 GENERAL Material properties as determined in accordance with the applicable ASTM A370 test procedures and Section F3 of the AISI Specification apply. For this purpose, tensile coupons are taken, after the completion of testing, from flat portions of the specimen at regions of low bending moment and shear force. V12a

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American National Standard ANSI MH16.1: 2012(R2019) Specification for the Design, Testing and Utilization of Industrial Steel Storage Racks

If the effect of cold-working is being accounted for by test, the test specimens must be formed by the same procedure as is used or contemplated in the prototype. This is essential because different manufacturing methods produce different amounts of cold working (e.g., cold working of a specimen by press-braking is less than that in a cold-roll-formed prototype). Test specimens are to be fully described prior to testing and any dents or defects shall be noted and the condition of welds, if any, inspected and described. All crosssectional dimensions of each specimen are to be measured prior to testing at several points along the length and photographs of specimens should be taken prior to, during, and after testing whenever it seems advisable. (The purpose of these tests is for design and not for purchase acceptance-tests.)

9.1.1

Testing Apparatus and Fixtures These tests should be carried out in a testing machine or by means of hydraulic jacks in a test frame or by application of properly measured weights. The testing machine or load-measuring apparatus must meet the requirements prescribed in the ASTM Methods E4, Verification of Testing Machines. The weights of load distribution beams and other fixtures are to be measured and included in evaluating the test data.

9.1.2

Instrumentation Dial gages or other deflection measuring devices are required at appropriate points to obtain proper alignment and to measure load-deflection behavior accurately. The deflections should be measured and reported to an accuracy of 0.03 inches (0.76 mm). Strain gages may be used if behavior characteristics other than ultimate loads and load-deflection relations are desired. In general, for coupon tests, extensometers are used. For members subject to twisting, such as channel and Z sections, the twist angle shall be measured by proper means.

9.1.3

Reduction and Presentation of Test Data For each test, the report is to include: 1. A sketch of the specimen with all dimensions. 2. A sketch of the test set-up with all dimensions, including locations and kinds of gages, loading and support arrangements and an identification of the loading apparatus (testing machine, jacks, etc.) with information on the range used and the smallest increment readable for that range. 3. The results of the coupon tension tests should be presented in the form of a table of elongations vs. loads or, alternatively, strains vs. stresses. Yield stress and ultimate strength shall be determined by any of the accepted ASTM methods. (It is desirable to include stress-strain curves in the data presentation.) 4. For presentation of the results of the test, all load, deflection, and other recorded data shall be properly reduced to actual values by correcting,

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American National Standard ANSI MH16.1: 2012(R2019) Specification for the Design, Testing and Utilization of Industrial Steel Storage Racks

where appropriate, for initial readings, weights of loading apparatus (e.g., loading beams), etc. These reduced measurements shall be presented in tables showing load vs. the particular measured quantity (deflection, strain, etc.). In the same tables, observations of special events (flange buckling, connection failure, etc.) shall be noted at the particular load at which they occurred. Graphic presentation of load-deformation curves is advisable at least for the midspan deflections depending upon observations made during the tests and on inspection of tabulated data, graphic presentation of selected or all other loaddeformation data is desirable, but optional as dictated by judgment.

9.1.4

Evaluation of Tests for Determining Structural Performance Tests are to be evaluated in accordance with Section F1 of the AISI [1].

9.2 STUB COLUMN TESTS FOR COLD-FORMED AND HOT-ROLLED COLUMNS 9.2.1

Test Specimen and Procedure The Q values of perforated compression members for use in Section 4 are determined by stub column tests as described in Part VIII of the AISI ColdFormed Steel Design Manual [4]. The ends of the stub column must be milled flat (preferably to a tolerance of 0.001 inch [0.025 mm]) and perpendicular to the longitudinal axis of the column. The axial load is to be applied by flat plates bearing (not welded or otherwise connected) against the milled ends. For the purposes of determining Q, only the ultimate strength of the stub column needs to be determined.

9.2.2

Evaluation of Test Results Q is calculated as follows:

Q=

ultimate compresive strength of stub column by test Fy A net min

where: Fy =

actual yield stress of the column material, if no cold work effects are to be considered; or the weighted average yield to point Fy, calculated in accordance with Appendix A 5.2.2 of the AISI [1], if cold work effects are to be considered.

Anet min = minimum cross-sectional area obtained by passing a plane through the column normal to the axis of the column. In no case shall Q be greater than 1. Where a series of sections with identical cross-sectional dimensions and identical hole dimensions and locations is produced in a variety of thickness, stub column tests need be made only for the largest and the smallest thicknesses (tmax and V12a

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American National Standard ANSI MH16.1: 2012(R2019) Specification for the Design, Testing and Utilization of Industrial Steel Storage Racks

tmin). Q values for intermediate thicknesses shall then be determined by interpolation according to the following formulas:

Q = Q min +

(Q max − Q min )( t − t min ) ( t max − t min )

where Q is the value for the intermediate thickness t, and Qmax and Qmin are the values obtained by test for the largest and smallest thicknesses, respectively. This interpolation is permissible only if the yield stresses of the two specimens do not differ by more than 25 percent and if the yield points of the intermediate thicknesses fall between or below those of the test specimens.

9.3 PALLET BEAM TESTS 9.3.1

Simply Supported Pallet Beam Tests These tests are acceptable only for beams that are not subject to significant torsional stresses or distortions. The simply supported pallet beam test is to be made only if the flexural behavior parameters such as the yield moment, ultimate moment and the effective flexural rigidity (EI) are to be determined. For the latter parameter, tests are to be conducted on two identical specimens unless a third test is required as specified in Section 9.3.1.3. If lateral restraints are required, the beams are to be tested in pairs as they would be used in completed assemblies.

9.3.1.1

Test Setup

The test set-up consists of a beam test specimen simply supported at each end (not connected to columns). The test load is applied to a load distribution beam which in turn imposes a load at two points on the beam which in turn imposes a load at two points on the beam specimen. Each load point on the beam test specimen is set at a distance of S/C from the support; where S is the span and C is a numerical value between 2.5 and 3. Plates can be used to prevent local failure at supports or at load points.

9.3.1.2

Test Procedure

After alignment, a small initial load of about 5% of the expected ultimate test load shall be applied to the test assembly to ensure firm contact between the specimen and all loading and support components. At this load, initial readings are to be taken from all gages. Loads shall then be applied in increments no larger than about one-fifth of the expected design load. Readings are taken for all load increments. (It is good to plot load verses mid-span deflection readings at each load increment during testing.) Noticeable deviation from straightness of such a plot will indicate incipient inelastic behavior or local buckling or crippling. When such is the case, load increments are reduced to no more than half the initial increments. (It is good practice, though not required, to measure permanent set for loads within the interval of 25% of the expected design load by reducing, within this interval, the ratio of the applied load to the initial load after the increment. Appropriate gage readings are to be taken at this reduced load to determine permanent set.) V12a

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American National Standard ANSI MH16.1: 2012(R2019) Specification for the Design, Testing and Utilization of Industrial Steel Storage Racks

When deflection increments for given load increments increase rapidly, this indicates the approach of ultimate failure load. If sudden failure is possible by the nature of the specimen, and if such sudden failure could damage the gages, they should be removed. On the other hand, if a gradual failure is expected, such as by simply yielding, it is desirable to measure the last center line deflections right up to and past the maximum or ultimate load, to obtain some part of the descending portion of the load deflection curve. All specific events noticeable by visual inspection, such as local buckling, crippling, failure of connections, etc., are to be recorded at the loads at which they occur.

9.3.1.3

Evaluation of Test Results

The parameters investigated shall be determined by test results by conventional methods. The flexural rigidity shall be calculated on the basis of the results of two tests of identical specimens, provided that the deviation from the average value does not exceed 10%. If the deviation from the average exceeds 10%, then a third identical specimen is to be tested. The average of the two lower values obtained from the tests shall be the result from the series of tests.

9.3.2

Pallet Beam in Upright Frames Assembly Test This test is intended to simulate the conditions in the actual rack as closely as possible.

9.3.2.1

Test Setup The test assembly shall consist of two upright frames not bolted to the floor and two levels of pallet beams with front-to-back ties when specified. The upright frame may be as high as desired. However, the bottom level beams shall be tested and shall be located so there will not be less than 24 inches (610 mm) clear between the test beams and the floor or between the test beams and the top-level beams. The end connections shall be those used in the prototype. The location of the test loads perpendicular to the beams shall simulate actual loading. If loads are to be applied by pallets or other devices resting on beams, it is important that friction between pallet and beams be reduced to the minimum possible amount by greasing or other means. (This is suggested because new, dry pallets on new, dry beams when used in the test could provide considerably more bracing than pallets and beams worn smooth in use and possibly covered with a film of oil.) The minimum instrumentation for such tests consists of devices for measuring the deflections of both beams at mid-span relative to the ends of the beams. One way of doing this is to attach a scale graduated to 0.01 inch (0.25 mm) at mid-span of each beam and to stretch a tight string (usually a string with a rubber band at one end) or wire attached to each end of the beam. Another way

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American National Standard ANSI MH16.1: 2012(R2019) Specification for the Design, Testing and Utilization of Industrial Steel Storage Racks

is to use dial gages at mid-span and at each end of the beams. Transits may also be used to read scales located at mid-span and at the end of the beams. Additional instrumentation, such as strain gages or additional dial gages at the ends of the beam, is needed only if special problems are to be considered. For highly unsymmetrical beams, e.g., deep channels or C-sections, it may be advisable to measure rotation under load. This is most easily done by rigidly attaching a protractor of sufficient size to the beam at or close to mid-span. A vertical string weighted at the end and acting as a plumb is then read against the protractor at every load increment.

9.3.2.2

Test Procedure The test procedures specified in Section 9.3.1.2 of this report shall be used.

9.3.2.3

Evaluation of Test Results The design load shall be the smallest of the following: 1. Strength determined according to the applicable provisions of the AISI [1] Section F and its subsections. 2. Two-thirds of the load at which harmful or objectionable distortions are observed in the connections or elsewhere. These distortions include rotations of such magnitude as to render the beam unserviceable. 3. The load (not including impact) at which maximum vertical deflections attain 1/180 of the span, measured with respect to the ends of the beams.

9.3.2.4

Number of Tests Required The number of tests for determining design loads shall be as specified in Section F of the AISI [1].

9.3.2.5

Deflection Test Once the design load has been determined as specified in Sections 9.3.1 through 9.3.2.3, an additional test shall be made using a new set of specimens. An initial load equal to the design load shall be applied, reduced to zero and the deflection read; this deflection reading shall be the zero reference reading. A load equal to 1.5 times the design load shall then be applied and the deflection read. The load shall then be held constant for one-quarter of an hour and the deflection read again. This deflection reading shall not exceed the previous reading by more than 5 percent. The load shall then be reduced to zero and the residual or permanent deflection read. The net residual deflection of the beam shall not exceed 15 percent of the final deflection measured at 1.5 times the design load. If these limitations are not met, the design load shall be reduced accordingly or the source of residual deflections determined and remedied, and the test repeated with new specimens.

9.4 PALLET BEAM-TO-COLUMN CONNECTION TESTS 9.4.1

The Cantilever Test This test is for determining the connection moment capacity.

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9.4.1.1

Test Setup

The test setup shall consist of a pallet beam at least 26 inches (660 mm) in length connected to the center of a column at least 30 inches (760 mm) in length. Both ends of the column shall be rigidly connected to rigid supports. The load shall be applied to the pallet beam at 24 inches (610 mm) from the face of the column. At this load application point, a dial gage shall be mounted to measure deflections.

9.4.1.2

Test Procedure

The test procedure specified in Section 9.3.1.2 shall be used.

9.4.1.3

Evaluation of Test Results

The design moment shall be determined in a manner similar to that specified in provisions 1 and 2 of Section 9.3.2.3.

9.4.2

The Portal Test This test is be used to obtain a joint spring constant needed for a semi-rigid frame analysis.

9.4.2.1

Test Setup

The test setup shall consist of two upright frames supported on four half-round bars, one under the base of each column, two beams the top of which is installed at a distance of 24 inches (61 cm) from the floor, and including front-to-back ties when specified. The half-round bars shall be located at the centroidal axes of the columns perpendicular to the beams. Extra plates may be placed between the base plates and the half-round bars, if necessary. The bases of the columns shall be held against lateral displacement but not against rotation.

9.4.2.2

Test Procedure

After the rack is properly assembled, a load equal to the design load of the beams shall be placed on the beams, simulating usual loading. A horizontal force equal to the horizontal design load corresponding to the vertical load on the assembly shall be applied to the assembly, equally distributed between the two columns on one side, at the level of the top of the beams, and in the direction of the beams. Deflection due to the horizontal loading shall be measured at the level of the top of the beams. The procedure shall be repeated at a load twice the design load.

9.4.2.3

Evaluation of Test Results

The spring constant is to be determined by rational analysis.

9.5 UPRIGHT FRAME TEST The frame tests specified in this section are intended to simulate the conditions in the actual rack as closely as possible. The purpose of the test is to determine the upright frame loads for an expected column failure that takes place between the floor and the bottom beam or between the two lower beams in a three beam-level test setup. V12a

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American National Standard ANSI MH16.1: 2012(R2019) Specification for the Design, Testing and Utilization of Industrial Steel Storage Racks

The test will account for vertical and horizontal loads as specified in Section 2.4.1 as well as the effects of semi-rigid connections. This procedure is also applicable to Sections 2.5 and 2.6 with adjustments to take into account modified loads and increased allowable stresses for Allowable Stress Design.

9.5.1 9.5.1.1

Horizontal Load in the Direction Perpendicular to the Plane of the Upright Frame Symmetrical Loading Condition

9.5.1.1.1 Test Setup The test assembly shall consist of three upright frames not bolted to the floor, and at least two levels of beams connecting the frames together to make two bays of pallet rack. When the distance from the floor to the first beam is smaller than the distance between beams, then three levels of beams shall be used. The vertical spacing of the beams shall be the same as in the actual application. The upright frame may be as high as desired; however, its construction consisting of a column and truss web members shall be of the same cross section, pattern and spacing as in the actual application. The top beam level and its column connection may be heavier or reinforced to the degree necessary to carry the test load to the point where the frame fails. The remaining beams and their connections shall be as in the actual application. This test load represents the loading from two or more beam levels. Horizontal loads shall be applied perpendicular to one outside upright frame at the centerline of the beam connection by means of either hydraulic cylinder(s) or by ropes and pulleys with hanging weights attached. The load at each beam level shall be applied equally to each column of the upright frame. To measure horizontal displacements, one scale shall be located at the centerline of each beam level, and another scale at midheight between the bottom beam level and the floor. All scales may be placed on one column. 9.5.1.1.2 Test Procedure 1. Align the rack structure so that it is level and plumb and so that all components are properly seated. 2. Take initial scale readings. 3. Place a vertical load equal to 1.5 times beam design load on each of the lower beam levels. 4. Take scale readings for horizontal movement. 5. Apply a horizontal load to the upright frame at each beam level. horizontal load shall be determined per Section 2.4.1.

The

6. Take scale readings for horizontal movement. 7. Apply one additional unit of vertical load to the reinforced top level beams only and take scale readings for horizontal movement. 8. Apply one additional unit of horizontal load to the reinforced top level beams only. Take scale readings for horizontal movement. (If hydraulic cylinders V12a

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American National Standard ANSI MH16.1: 2012(R2019) Specification for the Design, Testing and Utilization of Industrial Steel Storage Racks

are used, be sure the hydraulic cylinder at the bottom beam level is always applying the proper force to the upright frame.) 9. Repeat steps (7) and (8) until failure occurs in the upright frame. 9.5.1.1.3 Evaluation of Test Results The vertical design load for an upright frame shall be determined according to the applicable provisions of the AISI [1] Section F and its subsections. The tested ultimate load must be the last set of test data which has an equal number of both vertical and horizontal load increments. The tested ultimate load should be the lowest of the three tested conditions, namely symmetrical loading in Section 9.5.1.1, unsymmetrical loading in Section 9.5.1.2, or for the horizontal load in the direction parallel to the upright frame.

9.5.1.2

Unsymmetrical Loading Condition Test setup and test procedure are the same as Section 9.5.1.1 for symmetrical loading condition above, except that no load should be placed on one beam level in one bay directly adjacent to the expected column failure location. The direction of the horizontal load should be in the direction of sidesway.

9.5.2

Horizontal Load in the Direction Parallel to the Plane of Upright Frame

9.5.2.1

Test Setup The test setup is the same as in Section 9.5.1.1.1, except that the locations of horizontal loads and scales shall be changed so that the horizontal loads and displacements are in the plane of the upright frame.

9.5.2.2

Test Procedure The test procedure is the same as the procedure in Section 9.5.1.1.2 above, except in step (5) the distribution of the horizontal load on each beam level on each upright frame shall be as determined in Section 2.4.1. In order to compensate for the effect of the longer moment arm of the upper beam levels in the actual application, the applied test loads shall be modified such that the effect of the loads in the upper beam levels of the rack are properly accounted for both in overturning and shear force.

9.5.2.3

Evaluation of Test Results See Section 9.5.1.1.3.

9.6 CYCLIC TESTING OF BEAM-TO-COLUMN CONNECTIONS 9.6.1

General This protocol provides requirements for qualifying cyclic tests of beam-to-column moment connections in steel storage rack beam-to-column connectors for seismic loads. The purpose of the testing described in this document is to provide evidence that a beam-to-column connection has the strength, stiffness and rotational capacity to satisfy the demands that are being imposed upon them. Alternate testing requirements are permitted when approved by the

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American National Standard ANSI MH16.1: 2012(R2019) Specification for the Design, Testing and Utilization of Industrial Steel Storage Racks

Engineer of Record and the Authority Having Jurisdiction. It is also the purpose of this series of tests to determine the moment-rotation characteristics, or “dynamic spring relationship” of the beam-to-column connections of the various designs and manufacturers.

9.6.2

Definitions Definitions of the elements, components, variables, parameters, and dimensional characteristics of the physical test set-up will be specified as representative of this testing protocol.

9.6.3

Test Subassemblage Requirements The Test Subassemblage shall replicate, as closely as is practicable, the conditions that will occur in the Prototype during earthquake loading. The Test Subassemblage shall include a column element and two cantilever beam elements with integral attached beam-to-column connectors (See Figure 9.6.3-1).

Figure 9.6.3-1 Test Set Up

9.6.4

Essential Test Variables The Test Specimen shall replicate, as closely as is practicable, the pertinent design, detailing, and construction features, and the material properties of the Prototype.

9.6.4.1

Sources of Inelastic Rotation

Inelastic rotation shall be developed in the Test Specimen by inelastic action in the same members and connection elements as anticipated in the prototype, i.e., in the beam, in the column, in the panel zone, or within the connection elements.

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American National Standard ANSI MH16.1: 2012(R2019) Specification for the Design, Testing and Utilization of Industrial Steel Storage Racks

9.6.4.2

Size of Members

The size of the beams and columns used in the Test Specimen shall be representative of typical full-size storage rack beams and columns.

9.6.4.3

Connection Details

The beam-to-column connectors and the connection details used in the Test Specimen shall represent the Prototype connection details as closely as possible.

9.6.4.4

Material Strength

Each member of the connection element that contributes to the Inelastic Rotation at yielding will be tested to determine its yield stress and yield strength.

9.6.4.5

Welds

Welds on the Test Specimen shall satisfy and be performed in strict conformance with the requirements of Welding Procedure Specifications (WPS) as required by the American Welding Society (AWS).

9.6.4.6

Bolts

The bolted portions of the Test Specimen shall replicate the bolted portions of the Prototype connection as closely as possible.

9.6.5

Testing Procedure The testing program should include tests of at least two specimens of each combination of beam and column and connector size. The results of the tests should be capable of predicting the median value of drift angle capacity for the performance states of Strength Degradation and Ultimate Drift Angle Capacity.

9.6.6

Loading History-General Requirements Prior to the application of any cyclic loading, a constant downward load, Pc, of one kip shall be applied to each beam segment adjacent to each connector on both sides of the beam-to-column connection simulating the design downwardacting gravity pallet loads that serve to fully engage the beams and their connectors into the columns receiving them. The Test Specimen shall be subjected to cyclic loads according to the requirements prescribed for beam-to-column moment connections in Moment Frames. Other loading sequences may be used when they are demonstrated to be of equivalent or greater severity. Qualifying tests shall be conducted by controlling the Peak Drift Angle imposed on the Test Specimen. Loading will proceed with the application of equal displacements, D, at each end of each beam, and the measurement of the forces, PL and PR, corresponding to each such displacement.

9.6.7

Instrumentation Sufficient instrumentation shall be provided on the Test Specimen to permit measurement or calculation of the quantities required to produce meaningful, reproducible results for this testing protocol.

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American National Standard ANSI MH16.1: 2012(R2019) Specification for the Design, Testing and Utilization of Industrial Steel Storage Racks

9.6.8

Material Testing Requirements

9.6.8.1

Tension Testing Requirements

Tension testing shall be conducted on samples of steel taken from the material adjacent to each Test Specimen. Tension-test results from certified mill test reports shall be reported but are not permitted to be used in place of specimen testing for the purposes of this Section.

9.6.8.2

Methods of Tension Testing

Tension-test results shall be based upon testing that is conducted in accordance with the appropriate ASTM testing protocols for the particular materials being used.

9.6.9

Test Reporting Requirements For each Test Specimen, a written test report meeting the requirements of the Authority Having Jurisdiction and the requirements of this Section shall be prepared. The report shall thoroughly document all key features and results of the test. Additional drawings, data, photographs, and discussion of the Test Specimen or test results are permitted to be included in the report.

9.6.10 Acceptance Criteria The Test Specimen must satisfy the Strength and Rotational Demand requirements of this protocol for the connection, as applicable. The Test Specimen must sustain the required rotational demand for at least one complete loading cycle. The test results will also include the beam-to-column momentrotation characteristics and “dynamic spring relationship” for each of the combinations tested.

9.6.11 Evaluation of Test Results The design moment may be determined in a manner as shown in the Commentary Section 9.6.1. Other acceptable methods that lead to comparable results are permitted.

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10.

REFERENCES TO THE TEXT 1. American Iron and Steel Institute (AISI) (2007), North American Specification for the Design of Cold Formed Steel Structural Members, ANSI S100-07, Washington, DC: 2. American Institute of Steel Construction (AISC) (2010), Specification for Structural Steel Buildings, ANSI/AISC 360-10, Chicago, IL 3. American Iron and Steel Institute (AISI) (2008), Cold-Formed Steel Design Manual, Washington, DC. 4. American Society of Civil Engineers (ASCE) (2010), Minimum Design Loads for Buildings and Other Structures, ASCE/SEI 7-10, ASCE, Reston, VA.

5. American Concrete Institute (ACI) 318 (2011) Building Code Requirements for Structural Concrete, Appendix D, Farmington Hills, MI 6. Rack Manufacturers Institute (RMI) Specification for the Design Testing and Utilization of Welded-Wire Rack Decking, ANSI 26.2-2007

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Commentary to ANSI MH16.1: 2012(R2019)

Commentary to ANSI MH16.1: 2012(R2019) Specification for the Design, Testing and Utilization of Industrial Steel Storage Racks

An Industry Group of MHI 8720 Red Oak Blvd., Suite 201 Charlotte, NC 28217-3992 [emailprotected]

© 2019 by Material Handling Industry All rights reserved.

1

Commentary to ANSI MH16.1- 2012(R2019)

PREFACE TO THE COMMENTARY

Any structural design specification is the product of extensive research and development work combined with accumulated engineering experience. Rack structures differ in many respects from more familiar types of structures, such as buildings and bridges. It follows that the generally recognized principals and methods of design and testing of steel structures must be, modified and supplemented in those features peculiar to rack structures. This can be done adequately only by extensive analytical and experimental research on rack structures, combined with engineering experience in this field. It is important to bear in mind that the RMI Specification and the Commentary should not be used without first obtaining competent engineering advice with respect to suitability for any given application. This Commentary to the Specification, like those in the AISC and AISI Specifications referred to in section 10, attempt to serve two purposes: (1) they give explanations of, and reasons for, the various provisions of the Specification, and (2) where advisable, they suggest specific procedures with regard to engineering design, calculation or testing, which satisfy the particular requirements of the Specification. It should be emphasized that, while the provisions of the Specification are meant to be explicit, recommendations and suggestions made in the Commentary are not. In many cases they represent one way of interpreting the Specification provisions, but do not preclude other ways of doing so.

Published by

Rack Manufacturers Institute An Industry Group of MHI 8720 Red Oak Blvd., Suite 201, Charlotte, NC, 28217-3992 Telephone: (704) 676-1190 Fax: (704) 676-1199 www.mhi.org/rmi

© 2019 by Rack Manufacturers Institute All rights reserved. No part of this publication may be reproduced in any form, in an electronic retrieval system or otherwise, without prior written permission of the publisher, RMI. Printed in the United States of America.

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Commentary to ANSI MH16.1- 2012(R2019)

TABLE OF CONTENTS 1

GENERAL ...................................................................................................... 1

1.1

Scope .................................................................................................................................. 1

1.2

Materials ............................................................................................................................. 1

1.3

Applicable Design Specifications .................................................................................... 1

1.4 Integrity of Rack Installations .......................................................................................... 2 1.4.1 Owner Maintenance......................................................................................................... 2 1.4.2 Plaque .............................................................................................................................. 2 1.4.3 Conformance ................................................................................................................... 3 1.4.4 Load Application and Rack Configuration Drawings ....................................................... 3 1.4.5 Multiple Configurations .................................................................................................... 3 1.4.6 Movable Shelf Rack Stability ........................................................................................... 4 1.4.7 Column Base Plates and Anchors ................................................................................... 4 1.4.8 Small Installations ............................................................................................................ 5 1.4.9 Rack Damage .................................................................................................................. 5 1.4.10 Racks Connected to the Building Structure ................................................................. 6 1.4.11 Out-of-plumb and Out-of-straight Limits ...................................................................... 6

2

LOADING ....................................................................................................... 7

2.1

Load Combinations For the ASD design Method ........................................................... 8

2.2

Load factors and combinations for the LRFD design Method ...................................... 9

2.3

Vertical Impact Loads...................................................................................................... 10

2.4

Horizontal Forces ............................................................................................................ 10

2.5

Wind Loads ...................................................................................................................... 12

2.6 Earthquake Forces .......................................................................................................... 12 2.6.1 General .......................................................................................................................... 12 2.6.2 Minimum Seismic Forces .............................................................................................. 13 2.6.3 Calculation of Seismic Response Coefficient. ............................................................... 14 2.6.4 Connection Rotational Capacity .................................................................................... 18 2.6.5 Seismic Displacement ................................................................................................... 19 2.6.6 Seismic Separation ........................................................................................................ 20 2.6.7 Vertical Distribution of Seismic Forces .......................................................................... 20 2.6.8 Horizontal Shear Distribution ......................................................................................... 20 2.6.9 Overturning .................................................................................................................... 20 2.6.10 Concurrent Forces ..................................................................................................... 21

3

DESIGN PROCEDURES ............................................................................. 21

4

DESIGN OF STEEL ELEMENTS AND MEMBERS ..................................... 22

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Commentary to ANSI MH16.1- 2012(R2019)

4.1 Cold-Formed Steel Members .......................................................................................... 22 4.1.1 Properties of Sections.................................................................................................... 22 4.1.2 Flexural Members .......................................................................................................... 22 4.1.3 Concentrically Loaded Compression Members ............................................................. 23 4.2

5

Hot-Rolled Steel Columns .............................................................................................. 25

BEAM DESIGN ............................................................................................ 25

5.1

Calculations ..................................................................................................................... 25

5.2

Cross Section ................................................................................................................... 25

5.3

Deflections ....................................................................................................................... 26

5.4 Beam-to-column Connections ....................................................................................... 26 5.4.1 General .......................................................................................................................... 26 5.4.2 Beam Locking Device .................................................................................................... 26 5.4.3 Movable Shelf Racks ..................................................................................................... 27 5.5

Pallet Supports ................................................................................................................ 27

5.6

Welded Wire Rack Decking ............................................................................................ 28

6

UPRIGHT FRAME DESIGN ......................................................................... 29

6.1

Definition .......................................................................................................................... 29

6.2

General ............................................................................................................................. 29

6.3 Effective Lengths. ............................................................................................................ 29 6.3.1 Flexural Buckling in the Direction Perpendicular to the Upright Frames ....................... 30 6.3.2 Flexural Buckling in the Plane of the Upright Frame ..................................................... 36 6.3.3 Torsional Buckling ......................................................................................................... 38 6.3.4 Diagonals and Horizontals ............................................................................................. 39 6.4

7

Stability of Trussed-Braced Upright Frames ................................................................ 40

COLUMN BASE DESIGN ............................................................................ 40

7.1 Column Base Plates ........................................................................................................ 40 7.1.1 Bearing on Concrete ...................................................................................................... 40 7.1.2 Base Plate Design ......................................................................................................... 41 7.1.3 Maximum Considered Earthquake Base Rotation ........................................................ 41 7.1.4 Shims ............................................................................................................................. 41 7.2

Slab and Subgrade evaluation ....................................................................................... 42

7.3 Anchor Bolts .................................................................................................................... 42 7.3.1 Anchor Bolt Design ........................................................................................................ 42 7.3.2 Periodic Inspection of Anchor Bolt Installation .............................................................. 42

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8

SPECIAL RACK DESIGN PROVISIONS..................................................... 44

8.1

Overturning ...................................................................................................................... 44

8.2

Connections to Buildings ............................................................................................... 45

8.3

Interaction with Buildings ............................................................................................... 45

8.4 Pick Modules and Rack Supported Platforms .............................................................. 45 8.4.1 Posting of Design Loads ................................................................................................ 45 8.4.2 Design Requirements .................................................................................................... 46 8.4.3 Rack-Supported Platform and Pick Module Guards ...................................................... 46 8.4.4 Stairways ....................................................................................................................... 48 8.4.5 Product Fall Protection .................................................................................................. 48 8.5

9 9.1

Automated Storage and Retrieval Systems .................................................................. 48

TEST METHODS ......................................................................................... 48 General ............................................................................................................................. 48

9.2 Stub Column Tests for Cold-Formed and Hot-Rolled Columns ................................. 49 9.2.1 Test Specimen and Procedure ...................................................................................... 49 9.2.2 Evaluation of Test Results ............................................................................................. 49 9.3 Pallet Beam Tests ............................................................................................................ 50 9.3.1 Simply-Supported Pallet Beam Tests ............................................................................ 51 9.3.2 Pallet Beam in Upright Frames Assembly Tests ........................................................... 52 9.4 Pallet Beam-to-Column Connection Tests .................................................................... 52 9.4.1 The Cantilever Test ....................................................................................................... 53 9.4.2 The Portal Test .............................................................................................................. 54 9.5

Upright Frame Test .......................................................................................................... 56

9.6 CYCLIC TESTING OF BEAM-TO-COLUMN CONNECTIONS ........................................ 57 9.6.1 General .......................................................................................................................... 57 9.6.2 Definitions ...................................................................................................................... 58 9.6.3 Test Subassemblage Requirements ............................................................................. 58 9.6.4 Essential Test Variables ................................................................................................ 59 9.6.5 Testing Procedure ......................................................................................................... 61 9.6.6 Loading History .............................................................................................................. 62 9.6.7 Instrumentation .............................................................................................................. 63 9.6.8 Material Testing Requirements ...................................................................................... 63 9.6.9 Test Reporting Requirements ....................................................................................... 64 9.6.10 Acceptance Criteria ................................................................................................... 65 9.6.11 Evaluation of Test Results ......................................................................................... 65

10

REFERENCES ......................................................................................... 67

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Commentary to ANSI MH16.1- 2012(R2019)

Commentary on the Specification for the Design, Testing and Utilization of Industrial Steel Storage Racks 1 GENERAL 1.1 SCOPE The scope limits the applicability of the Specification to pallet racks, movable shelf racks, rack supported structures and stacker racks made of hot-rolled or cold-formed steel. Although, only these types of rack are explicitly mentioned, the Specification is also intended to be applied to any freestanding rack having a three dimensional structural system comprised of braced frames in one direction and moment frames in the other. In other words, any rack system that is constructed with beams and frames. Such rack types include, but are not limited to, push back rack, pallet flow rack. case flow rack and order picking modules. The Specification is also intended to be applied to the design of the storage rack portion of rack supported structures. The Specification is not intended to be a comprehensive design guide for the repair of damaged rack components. However, any repair made to rack components must be done in such a way as to restore the system to at least its original design capacity. Any repairs must be done under the advice and supervision of a design professional skilled in storage rack design. Further, it is necessary that the Load Application and Rack Configuration drawing(s) (see Section 1.4.4) be updated with the repair information. The rack systems that are excluded from the Specification (such as cantilever and drive-in) are excluded for two reasons. First, certain sections contained in the Specification do not apply to these rack types. For example, the upright frame and effective length provisions of Section 6 and the beam design provisions in Section 5 are not applicable to these rack types. Second, the Specification does not include the necessary design provisions for these rack types. For example, effective length factors and deflection limits for cantilever uprights would need to be included. Additional analytical work and testing is planned by the committee that will enable the addition of comprehensive design provisions for these rack types in the future. Some of the design sections and special test provisions of the Specification are applicable, and therefore helpful, in the design and testing of other rack types. For example, Section 4, Design of Steel Elements and Members, is applicable to any hot-rolled or cold-formed steel column of other rack types, such as cantilever or drive-in racks.

1.2 MATERIALS The intent of this section is to ensure that a reliable quality of steel is used in the fabrication of racks, without limiting the type of steel to any particular strength or rolling characteristics.

1.3 APPLICABLE DESIGN SPECIFICATIONS This Specification supplements or modifies the AISI [1] and AISC [3] 1

Commentary to ANSI MH16.1- 2012(R2019)

Specifications referenced in Section 10, which are necessitated by the special nature of rack structures, as distinct from regular framing for steel buildings. This edition of the specification allows the use of either Allowable Stress Design (ASD) or Load Resistance Factor Design (LRFD).

1.4 INTEGRITY OF RACK INSTALLATIONS 1.4.1

Owner Maintenance This section stresses the importance of planning in the initial design process, controlling the use of the rack to that initially intended, and scheduling regular inspection to maintain the integrity of rack structures. The user may wish to refer to FEMA 460 [5] for additional guidance on proper operation and maintenance for racks installed in areas accessible to the public.

1.4.2

Plaque In industrial and commercial warehouses, allowable floor loads are generally posted in easily visible locations, and such posting is often required by law. The Specification provides for similar posting of maximum permissible unit load for each given rack installation. For racks designed to receive loads on standard sized pallets, a unit load means the combined weight of product and pallet unless the installation provides for more than one unit load being stacked on top of each other. Load beams may be separately identified. A sample plaque is illustrated in Figures 1.4.2a and b. The figures are not intended to limit the plaque details, but rather are presented as possible examples. It is the intent of the Specification for the plaque to inform the storage facility manager of the safe rack capacity and any plaque that transmits the required information is acceptable. The manager of the storage facility shall have the responsibility to be cognizant of this load limit and to instruct all operating personnel to see to it that the permissible load is not exceeded.

Figure 1.4.2a Example of Load Capacity and Compliance Plaque for Palletized Loads 2

Commentary to ANSI MH16.1- 2012(R2019)

(1134 kg Total Unit Load) (11340 kg Total Load per Bay)

Figure 1.4.2b Example of Load Capacity and Compliance Plaque for Distributed Loads (366 kg/m2 Uniformly Distributed Load) (9072 kg Total Load per Bay) The plaques should not be transferred to any reconfigured or relocated rack without first verifying the applicability of the information on the plaque to the new configuration or location. 1.4.3

Conformance For racks designed in accordance with the Specification, it is important for building and safety inspectors to know whether they were produced and erected according to the Specification. To this end, Section 1.4.3 states that a plaque should be displayed indicating conformance with the Specification for racks so produced. The intent is that such a statement of conformance will greatly facilitate and simplify approval of rack installations by local, regional or federal inspecting authorities.

1.4.4

Load Application and Rack Configuration Drawings For purposes of safety inspection, complete data should be available on engineering design and capacity of the racks as originally ordered, delivered and installed. For this reason Section 1.4.4 provides that information, in the form of rack configuration drawings with load magnitude and application indications, be furnished by the rack dealer or manufacturer’s local representative involved in procuring and erecting the particular rack installation. The provision that both these parties retain such information on file is important because both the owner of the rack installation and the local dealer may change over the lifetime of the installation. The safekeeping of such information by both parties will greatly increase the probability that such information will be available if and when needed.

1.4.5

Multiple Configurations Most racks are produced so that they are adjustable and can be assembled in configurations different from the one originally ordered and installed. 3

Commentary to ANSI MH16.1- 2012(R2019)

Consequently, it is possible to install or modify a rack into an alternate configuration which is unsafe. For example, while using the original components (beams and upright frames) the rack could be rearranged to reduce the vertical distance between the upper beams, which would increase the unbraced length of the bottom portion of the columns. Its increased slenderness ratio would reduce the carrying capacity of the columns as compared to the original configuration. Alternately, racks can be modified by installation of additional components; e.g., greater number of shelf beams at smaller vertical spacing with the original upright frames. This would reduce the slenderness ratios of the individual column segments and increase their load capacities. However, the additional loads, which can now be placed on the greater number of shelves, could increase the load on the column by an amount greater than the increased capacity resulting from the reduction of the unbraced length. These are just two examples of changed configurations which could make an originally adequate rack unsafe. The owner or user of the rack installations will not have the engineering capability to establish the safety of his changed configuration. It is for these reasons that Section 1.4.5 provides that the owner be given comprehensive guidelines as to those alternate configurations which can be used safely. If changes, other than those detailed in the guidelines, must be made, the original manufacturer or competent storage rack engineer should be contacted. 1.4.6

Movable Shelf Rack Stability These racks differ from standard storage racking in that a majority of shelves are designed to be removed. In standard storage racks, shelves (beams) are readily adjustable, but cannot be removed without unloading the rack and re-assembling the components. For this reason, movable shelf racks are fitted with one or more permanent shelves and/or braces that provide the needed stability to the structure. This section specifies the provisions for identifying those stabilizing components, and for posting warnings and restrictions for removal.

1.4.7

Column Base Plates and Anchors It is the function of column base plates to receive the concentrated forces at the bottom ends of the columns and to distribute them with adequate uniformity over a large enough bearing area. Provisions for the dimensioning of column base plates on concrete floors are given in Section 7.2. Adequate connection of the column to the base plate is required to properly transfer the forces. This section also specifies that all rack columns shall be anchored to the floor. The anchor bolts shall be installed in accordance with the anchor manufacturer’s recommendations. Anchors serve several distinct functions: •

Anchors fix the relative positions of, and distances between, neighboring columns.

Anchors provide resistance against horizontal displacements of the bottom ends of the columns. A tendency for such horizontal 4

Commentary to ANSI MH16.1- 2012(R2019)

displacement may result from external lateral forces (earthquake, wind, impact, etc.) or from the horizontal reactions (shear forces) resulting from the rigid or semi-rigid frame action of the rack. If such shear forces would in fact cause horizontal displacements of the bottoms of the columns, this would reduce the carrying capacity of the rack as compared to computed values. For particularly tall and narrow racks, anchors may significantly increase the stability against overturning (see Specification Section 8.1). 1.4.8

Small Installations This section offers an exemption for small rack installations from the documentation provisions of Sections 1.4.4 and 1.4.5. These requirements would represent an excessive hardship for the management of such installations. However, in all other respects, the design, testing and utilization provisions of the Specification apply to all racks including the small installations as defined in this section.

1.4.9

Rack Damage Collisions of forklift trucks or other moving equipment with front columns are the single most important source of structural distress of storage racks. This section is concerned with the protection of those bottom portions of columns which are exposed to such collisions. At what exact level such collisions can occur depends on the detailed configuration of the particular forklift truck. It seems to be general experience that with existing equipment, collision occurs and the column damage is confined to below the first level of beams. When the lowest beam is located at some distance, say 2 feet to 4 feet (0.61 m to 1.22 m) from the floor, the rear counterweight of some trucks can impact the beam imposing a very significant horizontal load on the beam or frame bracing. In this case, impact protection of a special nature should be considered. While it is not practical to design racks to resist the maximum possible impact of storage equipment, this section addresses two possible ways to safeguard racks against the consequences of minor collisions. Users should contact the original equipment rack supplier or a rack accessory supplier for recommendations on products available. The first way is the provision for protective devices that will prevent trucks from hitting the exposed columns. Fenders or bumpers can and have been used for this purpose. Also, deflectors which, while not designed to withstand the full impact of the truck, are shaped to deflect it away from collision with the columns. No specific data is provided regarding the force for which such protective devices must be designed. It is the responsibility of the owner to specify, in the contract documents, the design requirements of the deflector. They will, of course, depend on the weight and velocity of the particular truck and also on such energy absorbing bumpers as may be provided on the truck itself. It is not necessary, that such devices fully maintain their own integrity in such collisions, but merely that they protect the columns from collision, even at considerable damage to 5

Commentary to ANSI MH16.1- 2012(R2019)

themselves. Therefore, such devices should be made to be easily replaceable or repairable in case of collision damage. A second method of safeguarding the rack upright is to reinforce the bottom portion of the front column and/or bracing in the frame. Common methods include welding an angle deflector to the front of the aisle side column, doubling the section strength by welding two columns together, using heavier horizontal and diagonal bracing to provide alternate load paths, or using larger base plates and anchors with the aisle side column. These methods are intended to aid in avoiding collapse of the frame due to minor impacts (not major collisions) and limit the damage caused. Users must perform regular inspections to ensure damaged racks are not used to store loads, and that adequate repairs are made promptly in consultation with the rack supplier. 1.4.10 Racks Connected to the Building Structure It is common practice to connect certain racks to the building structure for added stability, such as single rows adjacent to a wall. It is important, particularly in seismic applications, to consider the forces that can be applied to each of the structures, as well as, considering the structural interactions due to those forces. This section requires that the building owner be advised of the possible force imposed by the rack so that he can notify the building architect. The force transfer between any two structures is dependent on their relative movement and stiffness. Absent detailed knowledge of the other structure, it is generally not possible to compute the rack force being transferred. In such cases, the rack designer may provide forces assuming that the adjacent structure is infinitely stiff. The rack designer should also consider the alternative: the adjacent structure may transfer load to the rack. 1.4.11 Out-of-plumb and Out-of-straight Limits The purpose of these provisions is to keep the axial load eccentricity to a minimum. An out-of-plumb or out-of-straight condition will cause axial load eccentricity that will reduce the load carrying capacity of a rack column. The reduction can be significant. A rack that is out-of-plumb from top to bottom, or a rack column that is not straight, is likely to become further out-of-plumb or out-ofstraight when it is loaded. The limits on out-of-plumb and out-of-straight that are given in Sections 1.4.11.1 and 1.4.11.2 are for loaded racks. They are provided so the user may know when his racks may need to be re-plumbed and possibly repaired. If an empty rack exceeds these limits, it should be corrected prior to loading. Some installations may require tighter limits, for example, a structure that is loaded and unloaded by an automatic (unmanned) vehicle. 1.4.11.1

Out-of-plumb Limit

The limit given for top to bottom out-of-plumb in Section 1.4.11.1 is for a loaded rack and is not intended to be an installation tolerance. The installer should obtain the installation tolerances from the rack supplier prior to the start of an installation. These tolerances should be such that the loading of the racks will not cause the racks to exceed the out-of-plumb limit given in Section 1.4.11.1. 6

Commentary to ANSI MH16.1- 2012(R2019)

This limit is intended to prevent the use of racks that have a down aisle or a cross aisle lean. 1.4.11.2

Out-of-straight Limit

The out-of-straight limit is new in this edition of the specification and is given to prevent excessive “bows”, “kinks” or “dogleg” conditions that may exist in a rack column. A column could be plumb from top to bottom but have an unacceptable bow at mid-height, see Figure 1.4.11-1(a), or, a 20 foot (6 m) high column could be out 1 inch (25 mm) from top to bottom, which would be acceptable using a simple top-to-bottom out-of-plumb measurement, but the entire out-of-plumb could be between the floor and the 5 foot (1.5 m) level, see Figure 1.4.11-1(b). This dogleg condition would be very harmful. This condition could be caused by fork truck impact. The column could have a sine wave shape and be out-ofstraight as shown in Figure 1.4.11-1(c). The column could also be locally bent and exceed this limit, see Figure 1.4.11-1(d). As rewritten, the specification now prevents these situations from being acceptable if they exceed the 1/240 out-of straight limit.

Figure 1-1

2 LOADING The purpose of this section is to clarify the design methods used in the AISI [1] and the AISC [3] Specifications as they apply to storage racks and to show how the ASCE 7 [6] load combinations should be applied to storage racks. Storage racks differ from building structures in that their dead loads are a very small percentage of the total load when compared to buildings. Also, racks have product loads in addition to dead load and live load. Product load has been defined for racks as the products or pallet loads stored in the rack. This load is given the symbol, P, in the load combinations. Live loads could still be present in racks. Examples of live loads would be floor loading from work platforms or the moving equipment loads of Section 2.4.2. The load combinations have been written to agree with the load combinations from ASCE 7-10 [6] as they apply to storage racks with the addition of the product load (P) added to each combination. The vertical component of the seismic load on all but 7

Commentary to ANSI MH16.1- 2012(R2019)

the dead load has been dropped from the Specification to be consistent with the ASCE 7-10 requirements. Roof live load (Lr) for rack supported structures has been added since the 2002 edition of the RMI Specification. In the 2012 edition, the b term is introduced to provide more consistent treatment of vertical seismic forces from product load. Since the last edition of the RMI Specification LRFD design has become much more commonplace for cold-formed and structural steel. The AISI [1] and the AISC [3] have each combined LRFD and ASD in their respective specifications. The two methods of the analysis should give results that are similar but they will not be the same. The RMI requires the designs to be made according to the provisions for LRFD or to the provisions for ASD. The designer may see some benefit to the LRFD method due to the product load factor that has been incorporated in the load combinations. The Specification includes, in addition to the vertical load, provisions for vertical impact and horizontal loads that a normal rack installation will experience during its use. It is important to include all loads that could reasonably act together, but, also, not to combine loads that are unlikely to act together. For instance, one could reasonably expect that a forklift truck would not be placing the load on the rack during an earthquake. Therefore, it is not necessary to consider both shelf impact and earthquake loading acting concurrently.

2.1 LOAD COMBINATIONS FOR THE ASD DESIGN METHOD The ASD design method uses mostly unfactored applied loads and then compares them with nominal strengths divided by factors of safety. The 0.88 value is applied to the shelf plus impact critical because impact is a short duration load and for the two pallet case where the impact effects are not large, the beam design will result in the traditional factor of safety of 1.65 to 1. Other load factors that appear in the ASD method are due to changes in the ASCE 7 [6] combinations. All loads resulting from these combinations must be checked against nominal strengths from the AISC [3] or AISI [1] divided by the appropriate Ω (safety factors) given therein. The load Papp represents the product loading that must be present for the W or the E to be possible. It is recommended that this be the percent of the product load that was used to compute the base shear for the seismic analysis. For outdoor racks or rack structures with cladding Papp is zero for the wind uplift case because the racks may be required to resist the full wind force when they are empty. In load combinations #4, #5 and #7, all loads, except the dead load, are multiplied by 0.75. This change is made to reflect the same change in ASCE 7 [6]. Since the dead load of a rack structure is usually a small percentage of the total load, the use of the 0.75 factor is essentially the same as using the 33% stress increase that has been historically allowed when checking for wind or seismic cases. ASD load combination #10 exists to give a more realistic treatment of impact loading for shelves. See further explanation in Section 2.2 following. In this edition of the RMI Specification, the 0.75 is included in the equations, rather than described in a note as in previous editions. Equation 2 from the 2008 edition was broken into two equations to reflect the equations from ASCE 7 [6]. 8

Commentary to ANSI MH16.1- 2012(R2019)

2.2 LOAD FACTORS AND COMBINATIONS FOR THE LRFD DESIGN METHOD As stated above, product loads are the loads that are placed on storage racks. Product load has been differentiated from the live load so it can be factored differently. It is necessary to differentiate between these two types of loading because their treatment under seismic conditions is also different. The load combinations have been written to agree with the load combinations from ASCE 7 [6] as they apply to storage racks with the addition of the product load (P) added to each combination. The maximum product load is generally well known for a typical installation and more predictable because the weight and density of the product to be stored is known. The potential for overload may also be reduced due to the lifting limitations of the fork truck. For this reason a smaller load factor than that used for a live load is justified. However, the probability of a high product load being present during an earthquake is greater than the probability of a high live load being present, so for some of the loading combinations the product load factor is higher. The purpose of these modifications is to make the load combinations more realistic for the rack structures. These loads are to be compared with the nominal strength for the member or connection, multiplied by the appropriate resistance factor from the AISC Specification [3] or the AISI Specification [1]. The load factors and combinations have been updated to reflect similar changes made in ASCE 7 [6]. Roof live load (Lr) for rack supported structures has been added since the last edition of the RMI Specification. Product load has been added to the uplift case because, for racks, the product loads must be present in order for the prescribed seismic forces to act. It is possible to get an irregular loading that will produce seismic uplift on an unloaded column for an interconnected section of rack. The unloaded frames, in this case, would be tied to frames with pallet loading that would resist uplift. The seismic forces would, in turn, be less for the under-loaded areas. The conservatism here is that the product load not used to compute W is still present and resisting uplift. The modification of the LRFD approach is a reduced load factor, for product loads, of 1.4. As mentioned above, this is justified due to better predictability of product loads than live loads. The designer is reminded that this change applies to product loading only and does not apply to other live loading from roof, mezzanines and so on. The load factors for all of the combinations were derived by averaging the L factor and the D factor. This will result in a safety factor for the gravity load case of 1.65 for the entire range of column lengths with respect to product loading. The resistance factor () for compression members is 0.85 for cold-formed structural steel and 0.9 for hotrolled structural steel. LRFD load combination #8 exists to give a more realistic treatment of impact loading for shelves. This combination will usually govern the design of the shelf. For a two pallet wide shelf, which is most common, the impact effect is about 1/8 of the beam load so the margin of safety for this combination (with the D equal to 1 percent of the product load) would be:

(1.2×0.01×P ) + (1.4×P ) + (1.4× ( 0.125×P ) ) =1.587 P 9

Commentary to ANSI MH16.1- 2012(R2019)

For  = 0.95 This corresponds to the traditional 1.67 factor of safety. A resistance factor (b) of 0.9 would result in a higher factor of safety. This load combination would govern over combination #2 because combination #2 includes no impact. For ASD,

1.587

0.95

= 1.67

combination #2 could govern on a shelf with many loads applied, for example a shelf with 50 boxes hand stacked. Combination #8 will always govern for LRFD. The post installed anchor resistance factors have been removed from this section. The resistance factors are addressed in the anchor design requirements in Section 7.4.

2.3 VERTICAL IMPACT LOADS Handling of pallets being placed on and being removed from shelves is responsible for most beam damage. Considering the magnitude of the forces possible, no beam can be designed and guaranteed not to be damaged by a pallet being dropped onto the rack. An allowance for impact can therefore be no substitute for proper lift truck operation. How the lift truck is operated is the sole responsibility of the owner. The owner must make sure that drivers are properly trained and responsible, and that no one else can operate the trucks at any time. It must also be recognized that it is not possible to load a pallet without applying some impact to the shelf. When a pallet is loaded onto the rack, the impact force will be transmitted by the pallet being loaded. The pallet position should be chosen to ensure that the minimum safety margin exists for loading pallets at any location, Section 2.3 requires the impact force to be on one shelf distributed along the width of the pallet which causes the greatest stresses. When determining allowable loads by test, the impact load must be included in checking compliance with Section 2.3. The impact load should be applied by loading one pallet 125% of the test weight with all of the other pallets at the test weight. This will give an additional 25% of the test pallet load on each shelf. The heavy pallet may have to be placed in different locations to check bending moment, shear force and end connections. When testing or designing for deflection in accordance with Section 5.3, the inclusion of impact is not required. This impact provision is included to add extra safety to the design of the shelves and their connections due to vertical impact of loads being placed by the lift truck or other device. When 25% of one pallet load is added for impact on a two load wide shelf, the margin of safety is about 1.67 as shown in the Commentary Section 2.2. This is equal to the traditional margin of safety. If there is one load per shelf the margin of safety will be higher. For the shelf with many small boxes the margin of safety will be less and could approach 1.4/ or 1.47 minimum

2.4 HORIZONTAL FORCES There are few true horizontal loads imposed on a storage rack system. There are cases where horizontal forces may be generated that are addressed in other parts of the Specification, such as Section 2.5, Wind Loads, and Section 2.6, Earthquake 10

Commentary to ANSI MH16.1- 2012(R2019)

Forces, and the design of the storage rack components must be checked for those forces when applicable. Other horizontal loads are generally balanced out in long rack rows, such as plumbness or member out of straightness, or isolated, such as fork truck impacts, and it is not generally necessary to check the overall rack system for these loads. The local effects of possible fork truck impacts are addressed in Section 1.4.9 and, if columns are exposed to potential impacts, careful attention should be paid to the impact resistance. In the past RMI Specifications, an artificially high horizontal force was prescribed to be imposed in both the down-aisle and the cross-aisle direction of the rack. In the down-aisle direction the column members were required to be checked for axial load from the pallets and bending moments from this horizontal force. The horizontal force was a P force generated if the storage rack row leaned, in the down-aisle direction, 0.015 of the distance to the first shelf. It was found, in subsequent investigations, that this force had a severe impact on the capacity of an individual rack column. However, when many columns are installed in a row and interconnected the effect was balanced out. It is important to remember that design of a beam-column member requires the inclusion of P-∆ effects. Other specifications, NEHRP [7], and UBC [9], specify a drift limit for storage racks of 0.0125 hx and 0.0036 hx, respectively. These specifications do not require P analysis for drifts below the indicated limits. These codes state that if an analysis of the storage rack shows that the drift is within these limits, no analysis of the main force resisting components for P forces is required. The drift calculation for a column segment is straight forward. However, much of the down-aisle drift in a storage rack comes from the flexibility of the beam-to-column connection. The effect on the system of the various manufacturers’ beam to column connectors is generally difficult to analyze. If the connections are strong enough, generally, the overall rack system will also be sufficient. It is for that reason that a separate check of the strength of the connections is needed. Since the strength of many connectors cannot be analyzed, the connection test in Section 9.4 is recommended. In the cross-aisle direction there are generally not the quantities of members necessary to balance out the horizontal forces. The usual configuration is a back-toback rack row with two frames attached with back-to-back ties. Additionally, fork truck impact will have a greater effect in the cross-aisle direction. In the cross-aisle direction the frame bracing can generally accommodate a force of 1.5% of the frame vertical load. Similarly, in the cross-aisle direction, the connections of the bracing to the columns should also be checked. Some forms of storage rack also provide guidance for the top of the material handling equipment. In that case the equipment manufacturer will specify the top horizontal force and the frequency of that force. It is necessary that the force be included in the rack design in proper combination with the other forces on the system.

11

Commentary to ANSI MH16.1- 2012(R2019)

2.5 WIND LOADS There are instances where racks will be the main wind resisting structural system. Storage racks may be installed outdoors or they may be designed as a part of a rack-supported structure. When walls do not protect the rack system the wind will exert force primarily on the surface area of the pallet loads in the stored locations. Consideration should be given to unit loads of less than maximum weight but the same size as the posted unit load. Consideration should also be given to partially loaded rack where, for instance, a load is placed only in the top position and no others. The effects of wind acting on the rack components when empty or during construction should be considered. When a rack system supports a wall, consideration should be given in the design, especially for overturning, of racks that may be subjected to wind loading whether or not pallets loads are placed in the racks.

2.6 EARTHQUAKE FORCES 2.6.1

General It is important that rack systems be engineered, manufactured, installed, and utilized in a manner that such systems can perform adequately under all known loading conditions. Many geographic regions have building codes which are known to require that building and non-building structures, including rack systems, be designed to accommodate earthquake loads. The analytical approach to the seismic behavior of rack structures developed within the Specification is intended to reflect the current thinking within the Building Seismic Safety Council (BSSC) and their current provisions of the National Earthquake Hazards Reduction Program NEHRP [7], as well as the International Building Code [8] published by the International Code Council and American Society of Civil Engineers, ASCE 7 [6]. Should the rack structure be connected to another structure in a manner which significantly modifies the free field ground motions, then this structural interaction must be made part of the analysis and resulting design of both the rack system and the supporting structure. The principal advantage of mass-produced steel storage rack systems is their modular design, which allows considerable flexibility of configuration and installation. This advantage also presents a serious challenge to competent seismic performance. The initial installation of a rack system should be in accordance with an engineered design. Subsequent modifications should be made only with guidance by a registered design professional to avoid compromising the seismic integrity of the system. Further, storage rack systems are often subject to rough use and damage. It is the owner's responsibility to maintain the integrity of the rack to insure adequate structural performance during an earthquake.

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2.6.2

Minimum Seismic Forces The base of a rack system supported by a floor slab at or below grade experiences the ground accelerations directly, and the design should proceed accordingly. For a rack system supported by another structure (e.g., an upper story of a multi-story building structure) the structural analysis must consider the interaction between the structures. The system importance factors with magnitudes greater than one are intended to result in a higher performance level for certain rack installations under seismic conditions, viz., those within systems deemed to be essential facilities that should continue to perform following a seismic event; those which might release hazardous materials in such a seismic event; and those installations located in warehouse retail stores where the rack system is located in an area open to the general public. In such a warehouse retail store, unlike a sparsely populated typical warehouse and distribution center, large numbers of the shopping public can be expected to be within the rack system during business hours. The consequences of a rack failure, in this environment, dictate a higher level of performance for such systems. The Ip factor of 1.5 for warehouse retail stores is equivalent to having the racks being designed for maximum considered event performance, which is consistent with the stated performance goals of FEMA 460. The IP factor may be 1.0 if a displacement-based analysis is used. A displacement-based evaluation may include the movement of the pallets on the shelf beams. The movement of the pallet should not be more than what would cause the pallet to fall off the shelf beams for the cross-aisle analysis or the sum of the product load clearances for the down-aisle analysis. To properly account for the fact that the product loads placed on shelves are often less than the capacity for which the shelves are designed, the product load reduction factor (PRF) is introduced. Thus, in the longitudinal (or down-aisle) direction, where there are numerous repetitious pallet positions, Paverage is defined as the maximum total weight of product expected on the shelves in any row divided by the number of shelves in that row. Pmaximum is defined as the maximum weight of product that will be placed on any one shelf in that row, this being usually the design capacity for the pallet positions. With Paverage and Pmaximum, the Product Load Reduction Factor (Prf) becomes simply the quotient of the two. This reduction is not permitted in the cross-aisle direction. The factor of 0.67 applies to the loading considerations under seismic events. It does not apply to vertical load under any load combination nor to the fraction of vertical load used for restoring moment in the evaluation of seismic stability. Research has shown that there is some friction inducing, energy dissipating, relative movement between the rack and the stored product during seismic motions. The 0.67 factor represents the fraction of the dynamically active load on a fully-loaded system that is likely to be felt by a structure in a normal application, and that needs to be taken into account in the determination of lateral loads under seismic events. If the designer knows that for a particular installation the dynamic portion of the load is likely to be greater than 67 percent, 13

Commentary to ANSI MH16.1- 2012(R2019)

then such a higher magnitude should be used in the determination of lateral forces. Alternatively, the seismic design evaluation may be performed using a displacement-based method, such as the method described in Section 6.5.1 of FEMA 460 [4]. 2.6.2.1

Redundancy Factor A redundancy factor, ρ, is included in the design of rack. It only comes into effect for Seismic Design Categories D, E and F. Plan and Back Bracing is shown in Figure 6.3.2.1 (a) and the Braced Tower is show in Figure 6.3.2.1 (b). The factors shown in the specification are based on a standard storage rack configuration, with many semi-rigid beam-to-column connections down-aisle and frames braced with diagonals or horizontals and diagonals cross-aisle. Other configurations are permitted, but the redundancy factor must be adapted to suit each configuration. Redundancy in the cross-aisle direction can be shown to be satisfied by two frames, tied-together, with the frame diagonals oriented in the opposite directions. Under these conditions, the remaining diagonal brace(s) in tension and their connections and/or bending action of the unbraced columns and their connections can be shown to have a capacity of at least 67% of the demand to both frames.

2.6.3

Calculation of Seismic Response Coefficient. The seismic response coefficient is intended to be a site-specific value; the magnitude of this coefficient is affected by the characteristics of the structural system through the values of R and T, and also by the characteristics of the soil underlying the building on whose floors the rack system is founded, through the values assigned to the various soil profile types. T is the fundamental period of the rack structure. The factor R is an empirical response reduction factor intended to account for damping and the ductility inherent in the structural system at displacements great enough to surpass initial yield and approach the ultimate load displacement of the structural system. The factor R is not only a function of energy dissipation and ductility but reflects also the overstrength of the seismic system used. A specific procedure that may be used to justify larger R values is basing the procedure in FEMA P695 [28] “Quantification of Building Seismic Performance Factors”. Magnitudes of the spectral response acceleration SS and S1 are to be taken from the accompanying contour maps or USGS Open-File Report 01-437 “Earthquake Spectral Response Acceleration Maps” Version 3.10 as specified by the building code authority. Period computations must employ rational methods. The empirical equations for buildings are not applicable to storage racks, and cannot be used. There is no restriction on the period thus computed (ASCE 7 15.4.4). In the down-aisle 14

Commentary to ANSI MH16.1- 2012(R2019)

direction storage racks, typically, have much higher drifts than buildings, resulting in much longer periods than a building. There are several ways for estimating the fundamental period of vibration for a pallet rack in the down aisle direction. One method that is sometimes used is the Rayleigh Equation:

T = 2

W  g F 

2 i

i

i

i

where: WI = D + P (used to determine the seismic lateral forces) + 0.25L at each level i. For RMI Specification Section 2.6: D + 0.67P + 0.25L Fi = Seismic lateral force at level i. The force at each level must be computed from the force distribution equation required by the seismic design code. For the RMI Specification, these formulas are given in Section 2.6.6. g=

acceleration due to gravity (386.4 in/sec2) (9.81 m/s2)

T=

the fundamental period of vibration.

i = total lateral displacement at level i relative to the base, as computed using Fi. In order to use the Rayleigh Equation it is necessary to be able to compute the story lateral displacements. These values can be found by a rigorous frame analysis or by approximation. More accurate computations of the lateral displacements will result in a more accurate T value. If the second order lateral displacements are ignored or the drifts are otherwise underestimated the resulting T value will be conservative. The Horne-Davis method for frame analysis provides a simple method for computing lateral displacements at the beam levels. This method computes displacements as a function of Pcr, which is the elastic critical story buckling load of the column span. A summary is shown here:

Δp =

H×L +Δi-1 Pcr

where: p = primary story drift not including P- effects. H = total lateral force above the shelf elevation being evaluated. L=

column span length.

i-1 = Primary deflection just below the level being evaluated. 15

Commentary to ANSI MH16.1- 2012(R2019)

Pcr = critical elastic buckling load of the column span One of many methods used to compute the Pcr value is to calculate it using the value Kx for the column span. In this sense Kx is being used as a tool to approximate the effect of story buckling on the critical elastic buckling load of the column. Pcr could also be figured from a rigorous frame analysis or other equally acceptable methods. Computation of Pcr using the K method is shown below: where:

Pcr =

π 2 EI x

(KxL)

2

Kx = Effective length factor for story buckling in the down aisle direction as determined from Section 6.3.1.1. Ix = Column Moment of Inertia perpendicular to the plane of the frame. For the total drift at level i.

Δi =

Δp HL = Pcr -P 1- P Pcr

This method will be very accurate if the value of Kx is accurately determined. Kx for this method is a measure of the lateral stiffness of the story. If Kx is underestimated, the T value will be conservative. The designer should use the same Kx value to check column members as is used to determine T. The value of Kx used should not be more than is used for the member check. The period in the cross-aisle direction is usually much shorter. An alternate acceptable method of computing the period is provided in FEMA 460 [5] using the rotational stiffness F from Section 9.4.2.3.

Minimum seismic response coefficient Previous editions of the International Building Code referenced ASCE 7-05 which required that racks designed with the provisions of the RMI Specification have a minimum base shear coefficient of 0.14 SDS This minimum was imposed pending tests of the connections for rotational capacity. New rotational demand capacity criteria has been developed and new testing criteria developed that is provided now in Section 9.6. Testing of connections that has been performed in accordance with the criteria indicates that many connections, when tested, can satisfy the criteria. Therefore, the minimum has been reduced to 0.044SDS provided the connections used in designs satisfy the criteria of Section 9.6 and the Commentary for Section 9.6. Since the new criteria for connections and testing has been specified in this document, the minimum base shears are now the same as specified for all other structures in ASCE 7-10. 16

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2.6.3.1

Site Coefficients and Adjusted Maximum Considered Earthquake Spectral Response Acceleration Parameters The 2012 edition of the RMI Specification utilizes spectral response seismic design maps that reflect seismic hazards on the basis of contours. These maps were developed by the United States Geological Survey (USGS) and were updated in 2008. The USGS also developed a companion software program that calculates spectral values for a specific site based on a site’s longitude, latitude and site soil classification. The software program is the preferred method for establishing spectral values for design because the maps in Section 2.6.3.2 are too large a scale to provide accurate spectral values for most sites. A software program and maps may also be accessed at the USGS web site http://earthquake.usgs.gov/hazards/designmaps/ or through the RMI website at www.MHIA.org/RMI.

2.6.3.2

Seismic Design Category The Seismic Design Categories are a function of the seismic hazard at a site, the type of buildings (or occupancies) built at the site and the site-specific soil data, and is, therefore, more representative of the actual location of the project, and have replaced the old UBC seismic zones. The old UBC seismic zones (0 to 4) were based upon the seismic ground motion, corresponding to a certain probability of occurrence, within a zone. Therefore, all structures within a zone were designed for the same requirements, even though they did not need to be, nor did they take into consideration the type of building.

Figure 2-1 Seismic Design Categories, Site Class D

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Commentary to ANSI MH16.1- 2012(R2019)

2.6.4

Connection Rotational Capacity This section resulted from the report done in FEMA 460 [5]. Cd is the deflection amplification factor for a moment resisting frame and is obtained from Table 15.4-1 in ASCE 7 [6]. From FEMA 460 Cd =5.5 for the unbraced frames and Cd =3.5 for braced frames. The connection rotational capacity must exceed the maximum rotational demand. The demand may be computed directly using known earthquake records scaled in accordance with ASCE 7 [6], 16.1.4, as is done for buildings. This reduces the uncertainties in establishing α and Cd. Where available, as with buildings, such computations may be in lieu of the Section 2.6.4 requirements. At present, such analyses are not currently practical for everyday design office use. As a simplification, the demand equation in this section is an upper bound based on the assumption that the column and beam deformations are very small relative to the deflections due to connector rotation. The basic connector rotational demand may then be taken as the maximum earth displacement divided by the height of the rack (the top level is assumed stationary). While perhaps convenient, this formulation may obscure the origin of the displacement demand. It arises from expected maximum displacement of the ground, and is not any function of the structure itself. While not obvious, this formula is derived from ASCE 7 [6] equation 17.5-3 (which was used in developing the FEMA 460 [5] Appendix A equations). For example, at the Design Earthquake, the displacement demand would be:

Cd  s   =

gSD1T 4 2 B

(the B values are identified in FEMA 460)

Where T is the effective period of the rack determined using the effective stiffness of the rack at displacement Δ that has been appropriately modified to account for P-Δ effects. Engineers may wish to employ this alternate formulation to the complex FEMA 460 calculations. The connection rotational demand should include the effect of gravity load amplification. The column axial load used in the calculation of the gravity load amplification does not include the effective horizontal seismic weight factor, 0.67 on the P. This is because the entire product load contributes to the gravity load amplification portion of the drift. Since the seismic response of storage racks is a dynamic phenomenon, use of the full amplification 1/(1-α) is conservative for the seismic base and beam-tocolumn connection rotational demand analysis. The (1+α) term is used to account for only the first iteration of the second order effects. The intent is to obtain a reasonable estimate of these effects, not restrict the designer to any one method of obtaining them. Better estimates of the amplified effects of gravity load (shake table results or other time dependent computer modeling methods) may be used.

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Commentary to ANSI MH16.1- 2012(R2019)

In the equation for the connection rotational demand the 1+α term is to estimate the effects of gravity load amplification. Based on FEMA 460 the αterm is:

 k c +k be    k c k be  i=1  α=   k b k ce  k c +k be    Nc +N b      k c k be  k b +k ce    NL

W h pi

pi

where: Wpi = The weight on the rack that amplifies the drift. The 0.67 coefficient for the product load should not be used because the entire product weight amplifies the drift Wpi = ( PRF xP ) +D+0.25xL kc = Rotational stiffness of each beam-to-upright connection from testing in Section 9.6 kb =Rotational stiffness of each base plate connection (which may be assumed to be equal to kc for installations where there is at least one anchor bolt on opposite sides of the column in the down-aisle direction) Nc =Number of beam-to-upright connections Nb =Number of base plate connections kbe =beam end rotational stiffness assumed to be given by:

k be =

6EIb L

kce =bottom column end rotational stiffness assumed to be given by:

k ce =

4EIc H

When the ASD design method of analysis is used the seismic forces that are applied to the structure are only 67 percent of the forces that are applied using the LRFD design method. To compensate for this difference the seismic displacement at the top shelf level should be multiplied by 1.5 for computing Θd when the ASD design method is used. For both the ASD and the LRFD method, the seismic drift, Δs, shall be computed using the entire Wpi weight on the beams when using a second order computer analysis. 2.6.5

Seismic Displacement The connection stiffness used for the design of the components, upright and beams, should be the connection secant stiffness from testing consistent with the 19

Commentary to ANSI MH16.1- 2012(R2019)

base shear applied loads and resulting displacements. This will be a connection stiffness in the lower moment range. A possible starting stiffness could be the connection stiffness F from Section 9.4. When computing the seismic displacement ΔS, all loads used should be unfactored loads. The total earthquake force (E) should be used rather than 0.7E that is used for strength calculations in ASD. If the ASD-level earthquake forces are used, the displacement should be multiplied by 1.5 to obtain ΔS. 2.6.6

Seismic Separation For Seismic Design Category D and above, the seismic separation shall be checked using Section 2.6.6. This section allows a separation to be checked by analysis of the specific structure or by default distances given in the table for the braced and unbraced directions. Storage rack seismic displacement is less in the braced direction so the required separation is less. If an analysis is used to compute the seismic displacement, this analysis should be performed with all loads unfactored and the seismic force E (not 0.7E) applied to the rack as stated in Commentary Section 2.6.5. These separations are intended to include the effects of both the rack and the building structure. Amplification of the computed rack drift is felt to be adequate to accommodate the building drift.

2.6.7

Vertical Distribution of Seismic Forces The calculation of the vertical distribution of the lateral forces F, which are being resisted by the base shear V, results in a linearly increasing or triangular distribution for values based on the recommendations of FEMA 460 [5]. It is appropriate to account fairly for the contribution of the shelf-loading pattern on the development of the lateral forces, their distribution, and the resulting behavior of the rack structure. Thus, it is felt that when the bottom most pallet beam is within twelve (12) inches (305 mm) of the floor, such a shelf loading contributes little to the lateral deflections and resulting lateral force distribution along the height of the structure. However, when such a bottom shelf is located at an elevation greater than twelve (12) inches (305 mm) above the floor, the contributions will begin to be significant and should be considered in the same manner as the remaining loading on all the upper shelves.

2.6.8

Horizontal Shear Distribution The magnitude of the lateral shear force at any level is determined simply by the equations of equilibrium applied to the particular section of the structure. The story shear in any story is the sum of the lateral forces acting at all levels above that story.

2.6.9

Overturning The overturning checks are intended for only anchor uplift and floor reactions. The Specification requires two separate overturning checks. One is for the case

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Commentary to ANSI MH16.1- 2012(R2019)

of all storage positions loaded to 67% of the full rated capacity and the other for 100% in the top load position only. The overturning checks must be done considering the lateral forces acting at the elevation of the center of mass of the loads. 2.6.10 Concurrent Forces Considering the probabilities, it is not reasonable to expect that the effects of outof-plumbness, impact, wind forces, and seismic events will occur simultaneously. The design shall proceed accordingly.

3 DESIGN PROCEDURES This section specifies that engineering design calculations are to be made in accordance with accepted principals and conventional methods of structural design. This means among other things, that the basic concepts of structural analysis must be observed. This section also refers to the AISI [1] and AISC [3] Specifications as modified in various specifics in the Specification. The following is just one example of what is meant by “conventional methods of structural analysis”. Depending on types of connections, cross sections and relative capacities of beams and columns, pallet racks may function and be analyzed either as elastic rigid frames or as frames with semi-rigid connections. Regardless of what methods are used, the basic laws of equilibrium and compatibility must be satisfied in all parts of the structure. For example in the design of shelf beams, advantage can be taken of negative end moments up to values that can be developed by the specific connections, as determined by test (Section 9.4). However, if this is done, the column must be designed for the end moments which they must develop in order to create the end restraint used in the beam design. For instance, the upper end of a corner column has to support the full end moment of the abutting uppermost shelf beam, and the column must be designed for its axial load plus indicated moment. Unless this is done, the basic law of equilibrium has been violated. The same holds true at all other beam and column joints, except that the unbalanced end moment of two adjacent beams, is jointly resisted by both columns framing in to that joint and possibly also by the unloaded beam, if its connection can resist an appropriate moment. This is so because the negative beam moments can be calculated on the basis of conventional rigid frame analysis, or on the basis of semi-rigid analysis (i.e., using test values of connection capacities). By the simple law of equilibrium, no negative moment can act on the end of a beam unless the abutting members can develop this moment, and are designed for it. There may be situations in rack structures for which adequate design methods do not exist. This is the case where configurations of sections are used which cannot be calculated by established methods, where connections of a non-standard character are employed, etc. In these cases, design calculations of member and connection capacity, shall be replaced by appropriate tests. Several of these tests, peculiar to rack construction, are spelled out in later parts of the Specification. Tests not spelled out are to be conducted according to the general test procedure requirements of Section F1 of the AISI Specification [1]. 21

Commentary to ANSI MH16.1- 2012(R2019)

Tests are not permitted to be used in lieu of design calculations except in those situations which cannot be calculated by available methods. The AISI Specification [1] is quite specific about this in Section F1. It should be noted that confirmatory tests have a different nature and are covered in the AISI Specification [1] Section F2. Where tests are not specified in the Specification or the AISI Specification [1] for cold-formed members, the procedures in the IBC [8] Section 1714 and Section 1715 shall be used. No slenderness limitations are imposed on tension members. Indeed the AISC Specification [3] limitations themselves are not mandatory, but are only suggested as good practice.

4 DESIGN OF STEEL ELEMENTS AND MEMBERS Neither the AISI [1] nor the AISC [3] Specifications make provisions for perforated members of the type routinely used for columns and other components of racks. The effect of perforations on the load carrying capacity of compression members is accounted for by the modification of some of the definitions of these Specifications. The approach is to use the effective section properties based on the net section whereas the AISI Specification [1] bases the effective section properties on the unperforated section. Further information on the development of the AISI Specification [1] can be found in Reference 13.

4.1 COLD-FORMED STEEL MEMBERS 4.1.1

Properties of Sections

4.1.2

Flexural Members The RMI Specification approach involves the replacement of the section properties used in the AISI Specification [1] by the effective net section properties. The effective net section is the effective section determined based on the net section. Effective width equations do not exist for the type of perforations that are common in rack columns. For this reason approximate approaches need to be formulated. The area of the effective section for axial loading is determined by means of stub column tests according to Section 9.2. There are no test procedures for determining the effective section properties for bending. The approximate approach of this section was developed assuming that when the section is in tension local buckling does not reduce the capacity thus Q = 1 for the tension region. This assumption implies that the cold forming effects do not increase the axial tensile strength. In flexure, approximately half of the section is in compression and the other half is subjected to tension. Of course the effective section is not symmetric and, thus, this is an approximation. The effective area of the portion of the section in compression can be approximated conservatively by using the result of stub column tests. This is conservative because the web has a more favorable stress gradient when the section is in flexure. Thus the reduction factor for the area to account for local buckling when the section is in flexure is taken as the average of 1.0 for the tension portion and Q for the 22

Commentary to ANSI MH16.1- 2012(R2019)

compression portion, namely, 0.5 + Q / 2 . Thus, Se , the elastic section modulus of the effective net section at design yield stress, is determined by multiplying the net section elastic modulus by this reduction factor. The term Sc is the elastic section modulus of the effective net section at the lateral buckling stress of the gross section Fc. The reduction factor at the lateral buckling stress of the gross section is derived on the basis of the approach described in Reference 12 as:

1-Q  Fc 1 2  Fy

  

Q

In the calculation of Fe, ex, ey, and t the section properties are to be based on full unreduced gross section considering round corners except for j, xo and Cw which shall be based on the full unreduced gross section using sharp corners because the calculation of these parameters using rounded corners for the net section is extremely tedious. The extent of inelastic reserve capacity for perforated elements needs further study and is hence excluded in the Specification. 4.1.3 4.1.3.1

Concentrically Loaded Compression Members Effective Area Compression members can buckle in either of two ways: purely flexurally, i.e., by simple bending about one of the principal axes without twist; or torsionalflexurally, i.e., by bending accompanied by twisting of the member. Some types of members which buckle purely flexurally are: all closed box-type members, sections whose shear center and centroid coincide, which is true for doublysymmetrical members (e.g., I-sections), equal flange Z-sections, and others. Many other open thin walled shapes can be subject to torsional flexural buckling, such as singly symmetrical channel-, C-, hat-, and plain or lipped angle-sections, and others. In all these shapes, centroid and shear center do not coincide. However, whether such members actually will buckle torsional-flexurally or just flexurally in the direction of the axis of symmetry depends not only on the type of cross section but also on its relative dimensions. Thus, channels with wide flanges tend to buckle torsional-flexurally, while narrow-flanged channels generally buckle only flexurally. In designing columns for flexural buckling without torsion, the effective length factors K shall be taken as specified in Section 6.3 of the Specification. For singly symmetrical shapes these methods are quite straightforward, provided that the effective length is the same for bending about the axis of symmetry (x-axis) and for twisting. This is generally the case for building-type frames, but need not be so for rack structures. For instance, for a pallet rack with channel or Ccolumns placed so that the x-axis is in the plane of the upright frame, the unbraced length Lx for buckling about the x-axis is the length from the floor to the 23

Commentary to ANSI MH16.1- 2012(R2019)

center line of the bottom beam, or between successive beam center lines, as the case may be. (This is the unbraced length Lx, not the effective length KxLx.) However, for torsion it can be assumed that even light members, such as the diagonal or horizontal struts of upright frames, will prevent twisting at the point where they are connected to the columns, provided the connection itself does not permit twist. Typical connection details between the columns and the bracing which are expected to inhibit twist and those that are not are shown in Figure 6.3.3-1. For those racks with proper connection details, the unbraced length Lt for torsion will be the free length between adjacent connections to any members which counteract torsion. For instance, if a diagonal of an upright frame meets the column somewhere between the floor and the lowest beam, then the longer of the two lengths, from the diagonal connection to either the floor or the beam, represents the unbraced length for torsion, Lt. Different effective lengths for torsion and flexure are accounted for by taking K xLx in the expression for ex, and KtLt in the expression for t. The effective length factors Kx and Kt are given in Sections 6.3.1 and 6.3.3, respectively. The treatment of concentrically-loaded perforated compression members is based on a modification of the AISI Specification [1] approach for unperforated compression members. The modification is based on the studies reported in Reference 15. The procedure consists of obtaining the nominal axial load capacity by multiplying the nominal failure stress obtained for the gross section by the effective net area obtained at the nominal failure stress. In general, the effective net area cannot be calculated for column sections with the types of perforations typical in rack structures. For this reason the effective net section area is to be determined through the use of the following formula which was developed in Reference 12: Q   Fn   A e = 1- (1-Q )    A NetMin  Fy       

where the Q factor is determined by the procedure specified in Section 9.2. 4.1.3.2

Distortional Buckling Singly symmetric compression members may be subject to distortional buckling effects. Methods using a finite strip analysis accounting for the perforations may be used for sections with perforations. Other methods, such as but not limited to finite element methods, generalized beam theory or structural testing, are also acceptable.

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4.2 HOT-ROLLED STEEL COLUMNS

5 BEAM DESIGN 5.1 CALCULATIONS 5.2 CROSS SECTION For pallet rack and stacker rack beams, this section states that the load effects shall be determined by conventional methods of calculation, if the shape of the cross section permits. In general, the usual simple formulas for stresses and deflections of beams apply only if the cross section is symmetrical about the loading direction, i.e., if the section has a vertical axis of symmetry. Beams of any other cross sectional shape may twist under load. Such twist can reduce the carrying capacity of the beams, and/or result in deflections larger than that determined by conventional computations. Examples of such sections are channels, particularly those with wide flanges, and wide flanged C-shapes when placed with web vertical. Since calculations that include the twist are fairly complex and not always reliable Section 5.2 calls, instead, for test determination. It is worth noting that closed box shapes, even if they have no vertical axis of symmetry, are much less subject to twist than open shapes. Thus, in many cases of closed unsymmetrical box beams, determination by conventional calculations may prove adequate. It can be shown that the following equation can be used to account for the effect of end fixity in determining the maximum midspan moment Mmax of a pallet beam considering semi-rigid end connections:

M Max =

WL rm 8

where:

rm =1E=

2FL 6EIb +3FL

the modulus of elasticity

F= the joint spring constant determined either by the Cantilever Test described in Section 9.4.1 or by Pallet Beam in Upright Frames Assembly Test described in Section 9.3.2. Ib =

the beam moment of inertia about the bending axis

L=

the span of the beam

W=

the total load on each beam (including vertical impact loads)

Me =

the beam end moment

where:

Me =

wL (1-rm ) 8 25

Commentary to ANSI MH16.1- 2012(R2019)

In the above derivation the load is assumed to be uniformly distributed. For a value of F equal to zero, Mmax=WL/8 is obtained. The specification requires applying a vertical impact factor of 25% to one unit load. For a pair of pallet beams supporting two pallets this would mean that the load on one half of the beam will be 25% more than the load on the other half. The maximum moment will not occur at midspan in that case. However, it can be shown that the magnitude of the maximum moment thus computed will be within 1% of the moment computed on the basis of distributing the total load uniformly. If one considers semi-rigid joints, the following expression for maximum deflection max can be derived.  Max =  ss rd

where:

δss = rd =1-

5WL3 384EIb

4FL 5FL+10EI b

5.3 DEFLECTIONS The 1/180 of the clear span is an industry consensus figure based on visual appearance and operational clearance considerations.

5.4 BEAM-TO-COLUMN CONNECTIONS 5.4.1

General The beam end connections must be designed to resist the forces and moments obtained from the structural analysis. The effects of eccentricity of the connection and the effect of rotation of an attachment to the edge of an unstiffened flange must be evaluated. The influence of these connections on the overall behavior is significant (see Section 5.3). Particular attention should be directed to the column-to-bracing connections.

5.4.2

Beam Locking Device The upward load is specified to prevent accidental disengagement of the beam connection. The upward force should be applied to an unloaded beam. Since this load is compared to the connection locking device failure there is no load factoring required. Failure of the locking device is defined as the distortion of the locking device that prevents reapplication of upward force, removal, reinstallation, or reduces the carrying capacity.

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Commentary to ANSI MH16.1- 2012(R2019)

5.4.3

Movable Shelf Racks The upward load is specified to prevent accidental disengagement of the beam connection. The upward force should be applied to an unloaded beam. Since this load is compared to the connection locking device failure there is no load factoring required. The phrase “connected to each other rigidly” indicates that the beams are connected such that skewing of transverse members will be prevented in normal use.

5.5 PALLET SUPPORTS In general, a properly placed stored unit that is on a pallet that is structurally sound will adequately support the product on the pallet spanning between the beams. In that case, additional supports may be unnecessary. In the absence of information to the contrary, it is customary for the rack system designer to assume that the warehouse operator will be using, throughout the entire warehouse, pallets that are adequate to support the load spanning between the shelf beams. Based on the operation of the warehouse, though, there may be the potential for the pallet to be misplaced on the shelf beams in such a way that the edge of the pallet does not rest on the shelf beam. In this case, if pallet supports are requested by the warehouse operator, they shall be designed to support a structurally sound pallet in its worst location on the shelf. It can be shown that, for the end attachment load it will be when the edge of the pallet is directly next to the shelf but not resting on that shelf. For span bending of the pallet support, this position may be when the center of gravity of the pallet is equidistant from one beam as the edge of the pallet is from the other (a = ec in the figure below).

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Commentary to ANSI MH16.1- 2012(R2019)

For the maximum bending condition the moment is equal to: 2

𝑀𝑀𝑎𝑥 =

𝑊(𝐿 − 𝑑⁄2) 4𝐿

 L-d  W  2   M Max = L

2

where: W = Maximum load applied to one pallet support. L = Clear span between the shelf beams d = Depth of the bottom of the pallet ec = center of gravity of the load to the closest supporting beam However, there are a number of situations that may require the use of a Pallet Support to aid in the support of the pallet when on the shelf. The bottom configuration of the pallet may be such that the pallet will not be supported on the beams. Further, there may be a potential for the introduction into the storage system of pallets that are not structurally sound and/or not capable of supporting the stored products that will need pallet supports underneath to support the pallet and stored products. In these cases it is important that the warehouse operator inform the rack system designer of the specific details of the pallet bottom configuration and of the structural attributes of the pallet and load so that the rack designer may properly design the pallet support for these conditions.

5.6 WELDED WIRE RACK DECKING Wire decking is a decking system used on pallet rack shelves. Its purpose is to provide additional support for stored materials, as well as, becoming a safety net for unstable loads. Wire decking is fabricated from welded-wire mesh, and usually has reinforcements in the form of channels or support wires. Wire decks are supported by the rack beams at the front and rear and the strength and stiffness of the wire deck system provides support for the load between the beams. Decking designs vary greatly depending on the application. Wire thickness, grid pattern and number of channels all have an effect on performance. Wire decking is unique to other types of shelving not only in appearance but also in performance. Because wire decks are made of steel, their integrity, capacity and performance remain constant. The advantages of wire mesh decks include safety, greater capacities, their ability to allow light, air, debris and water (very important in some states due to fire codes) to pass through the decks.

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6 UPRIGHT FRAME DESIGN 6.1 DEFINITION 6.2 GENERAL 6.3 EFFECTIVE LENGTHS. The AISI [1] and the AISC [3] Specifications use the effective length concept in determining the load carrying capacity of a member subjected to an axial load alone, or in combination with bending moments. Such a member is usually part of a frame. The effective length method is not the only available technique for determining the axial capacity of a compression member. Alternative methods, consistent with AISC and AISI are equally acceptable. Where large lateral load requirements already exist (such as the higher seismic design categories) a method employing the lateral load may dominate the instability considerations in the design and a K factor approach may not be required. The effective length factor accounts for the restraining effect of the end conditions or the effect of the members framed into a particular member. The effective length concept is one method for estimating the interaction effects of the total frame on a compression member being considered. The RMI has chosen to use the K factor approach, but does not preclude the use of other properly substantiated methods. Several references are available concerning alternatives to effective length factors for multilevel frames under combined loads or gravity loads alone. Work has been done for hot-rolled members and the RMI has co-sponsored, with AISI, ongoing research for cold-formed members. General discussions of the effective length concept can be found in Reference 22. Basically, the effective length factor, K, times the unbraced length, L, gives the length of a simply supported column which would have the same elastic buckling load as the particular member which is part of a frame or which has other end connections. Though the effective length is computed on the basis of elastic frame behavior, it is general practice to use the effective length approach to find the inelastic load carrying capacity. This is the approach taken in the AISI [1] and the AISC [3] Specifications as well as in the Specification. As discussed in connection with Section 4.2.2, the effective length approach is extended to the torsional-flexural buckling mode as well. The behavior of rack structures and hence the effective length factor depends on the unique design of racks, such as the rigidity of the connection between columns and beams. Due to the wide variety of details and cross sectional dimensions in rack structures, the effective length factors vary within a very broad range. For example, a simple portal frame with pinned column bases, the effective length factor approaches infinity as the connection between the beam and the columns approaches a pinned condition due to the connection details. The values of the effective length factors given in the Specification are by no means maximum values. They are the average values assuming the racks to be designed according to good engineering practice and judgment. In all cases rational analysis would indicate whether the stipulated values are too conservative or too 29

Commentary to ANSI MH16.1- 2012(R2019)

unconservative for the particular rack. Possible rational analysis procedures are presented later in this commentary. 6.3.1

Flexural Buckling in the Direction Perpendicular to the Upright Frames The buckling considered here is parallel to the aisle. In general, racks have singly symmetric sections for columns and also in general the axis of symmetry is perpendicular to the aisle. The buckling of such sections parallel to the aisle, namely, about the axis of symmetry takes the form of torsional-flexural buckling. For such cases, the effective length factor is intended to be used in computing ex in Section 4.2.2, ex is in turn used in computing the torsional-flexural buckling load.

6.3.1.1

Racks Not Braced Against Sidesway This section is applicable to racks that do not meet the bracing requirements of Section 6.3.1.2. The side-sway failure of several columns in a down-aisle direction is quite catastrophic. Portions of rows or entire rows collapse. A value of Kx greater than 1.0 is used to design against this type of failure. The theoretical lower limit of K is 1.0 in braced framing, or for full fixity at the top and the bottom of an unbraced column. Since full fixity is never achieved and the unbraced columns are free to translate, K will always be greater than 1.0 for unbraced frame design. The actual value of K depends on the rotational restraint at the top and the bottom of the column. Pallet racks that use semi-rigid connections will have Kx values much greater than 1.0 and may even exceed 2.0. The Specification allows the use of Kx = 1.7 as a default value. Numerous typical rack assemblies were researched. These rack assemblies had Kx values ranging from as low as 1.3 to as high as 2.4. The racks with high K values had lighter beams and heavy columns. A larger number of bays tend to increase the K values because the supporting action of lighter loaded end frame columns diminishes. As the number of bays increases the probability of having all the bays fully loaded decreases. Thus, as the number of bays increases the probability of getting a higher K may not increase. A three bay rack has a greater probability of being fully loaded than racks with more bays. Thus, practice has shown that a three bay rack may be more likely to fail by sidesway. The number of levels also has an influence on the value of K. As the number of fully loaded levels increase the value of K also increases. This is because the difference in loads in the lowest level and the second level columns decreases as the number of stories increases. When the difference in the loads decreases, the value of K increases. A value of K equal to 1.7 was chosen to give a reasonable amount of protection against sidesway for most common rack configurations. The designer should be aware that K may actually be greater than or less than the default value of 1.7. If the default value of 1.7 is used no further reductions may be taken based on utilization because utilization has already been considered in the selection of this value. K values other than 1.7 may be used if they can be justified on the basis of rational analysis. The rational analysis must properly consider column stiffness, beam stiffness, semi-rigid connection behavior and base fixity. The common 30

Commentary to ANSI MH16.1- 2012(R2019)

approaches to evaluate K are frame analyses that compute the frame buckling loads directly and alignment charts. The latter approach will be discussed below. The use of alignment charts to determine effective length coefficients is described in References 3 and 22. The procedures described in this reference need to be modified as described below to account for the semi-rigid nature of the connection of the columns to the floor and to the pallet beams. The floor is assumed to be a beam with the following stiffness:

If bd 2 = Lf 1440 where: b=

the width of the column (parallel to the flexure axis)

d=

the depth of the column (perpendicular to the flexure axis)

The floor is assumed to be concrete, and the column connection to the floor must be adequate to develop base moments consistent with this stiffness. For other floor material the equation should be modified. In the analysis the stiffness of the pallet beams is to be reduced by (Ib/Lb)red due to the semi-rigid nature of the joints.

 Ib  Ib Lb   =   Lb red 1+6 ( EIb )  L F ( b )  where Ib =

the actual moment of inertia of the pallet beams

Lb =

the actual span of the pallet beams

F=

the joint rigidity determined by the Portal Test of Section 9.4.2

E=

the modulus of elasticity

The analysis for the effective length factor for the portion of the column from the floor to the first beam level would involve the following G values as defined in the commentary of AISC [3].

Ic  1 + 1  Lc1 Lc2  Ga =  I 2  b   L b red

Ic Gb =

If

31

Lc1 Lf

Commentary to ANSI MH16.1- 2012(R2019)

where Ic

the column moment of inertia

Lc1 the distance from the floor to the first beam level Lc2 the distance from the first beam level to the second beam level The effective length factor is then found directly from References 16 and 17 on the basis of Ga and Gb. The expression used above for If/Lf is based on References 17 and 18. The expression given in these references are modified to reflect the situation for rack columns, which, in general, have thin base plates. This expression is a crude representation of the base fixity. The base fixity depends among other parameters, on the ratio of the base moment to the axial load, namely the eccentricity of the axial load. A general formulation would be quite complex. Though direct test data is not available it seems reasonable to expect that the above equation would estimate the fixity rather closely for eccentricities corresponding to design load and 1.5% lateral loads. This reference, using the above procedure, reaches reasonably satisfactory correlation between the computed and the observed test results. It must be noted, however, that the base fixity is just one of many properties of the rack that affect the structural behavior. The expression for If/Lf given above assumes that the floor is concrete. The joint rigidity F is to be determined by a portal test. As the frame sidesways as the type of buckling under consideration implies, the beams of the frame will have different joint rigidities at each end. This is due to the fact that at one end the rotation is increased while the rotation is decreased at the other end. The portal method yields an intermediate value between the values of the rigidities of the two ends. 6.3.1.2

Racks Braced Against Sidesway A rack structure, in order to be treated as braced against sidesway, must have diagonal bracing in the vertical plane for the portion under consideration. This would restrain the columns in the braced plane. In order to restrain the columns in other planes, there need to be shelves which are rigid or have diagonal bracing in their horizontal plane as specified in this section. (Some of the terms used above are illustrated in Figure 6.3.1.2 (a).) The function of this rigid or braced shelf is to ensure restraint for the other row of columns against sidesway with respect to the braced row of columns. All bracing should, of course, be tight and designed for its intended use. Horizontal movement, or translation, of the front column relative to the rear column of rack with bracing in the rear vertical plane can, in some cases, be prevented by the presence of pallets on the load beams. To prevent translation of the front column, the frictional forces between the pallets and the load beams must be capable of resisting horizontal force perpendicular to the plane of the upright. The magnitude of this force at a bracing point should be at least 1.5% of the column load immediately below the beam acting as the horizontal brace. 32

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Whether or not sufficient force exists to prevent translation must be determined by rational analysis giving full consideration to factors such as, but not limited to, lighter than normal loads and the absence of any or all loads. Under typical warehouse conditions, the coefficient of friction between a wood or metal pallet and its supporting beams has been the subject of many tests and can conservatively be taken as 0.10. Special consideration is necessary in cold storage freezers where operational procedures can produce ice on the contact surfaces. Representative tests are recommended in this and other conditions, such as greasy or oily environments, where they would likewise be warranted. In order to cut down the unsupported lengths of the columns, the diagonal bracing should divide the brace plane as shown in Figures 6.3.1.2 (b) and (c). At the same time rigid or braced fixed shelves are to be provided at levels AA in order to have unsupported lengths of h as shown in the figures. If such shelves are not provided at levels AA, then the column will be designed in accordance with Section 6.3.1.1. The bottom and top portions of columns in Figure 6.3.1.2 (d) are to be designed as columns in an unbraced rack, whereas those in the mid-portion as columns in a braced rack. A rational analysis similar to that described in Section 6.3.1.1 of this commentary can also be used for racks braced against sidesway. In this case the following changes need to be made:

If bd 2 = L f 240 and

Ib  Ib  Lb   =   L b  red 1+2  ( EI b )   L F ( ) b  

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Figure 6.3.1.2 (a) Plan and Back Bracing

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Figure 6.3.1.2 (b) Bracing Tower (with addition of bracing on aisle side of columns)

Figure 6.3.1.2-1 Racks Braced Against Sidesway

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6.3.2

Flexural Buckling in the Plane of the Upright Frame In rack structures the columns are usually either singly symmetrical shapes with the axis of symmetry in the plane of the upright frames or doubly symmetric shapes. Because of this, buckling in the planes of the uprights is usually flexural. Upright frames have a wide variety of bracing patterns. The most effective bracing pattern is one where the centerlines of braces and the columns intersect at one point as shown in Figure 6.3.2-1 (a). This is because the braces restrain the columns by virtue of their axial stiffness. On the other hand, the bracing action in the system shown in Figure 6.3.2-1 (b) depends on the flexural rigidities of the braces and the connections between the columns and the braces. Thus this type of bracing is not as effective. The effective length factor for the frame of Figure 6.3.2-1 (a) can be taken usually as 1.0. This assumes that the braces are adequate and the connection between the braces and columns are sufficiently rigid in the axial direction of the braces. The effective length factor for the frame of Figure 6.3.2-1 (b) is usually greater than one and can be found by rational analysis.

(a)

(b)

Figure 6.3.2-1 Braced and Unbraced Frames In rack structures, frequently, the centerlines of the horizontal and the diagonal braces and the centerline of the column do not meet at one point. Thus, the bracing arrangement falls between the extremes illustrated in Figures 6.3.2-1 (a) and 6.3.2-1 (b). The following three subsections treat various bracing configuration possibilities.

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6.3.2.1 6.3.2.2 Upright Frames with Diagonal Braces or a Combination of Diagonal and Horizontal Braces that intersect the Columns are illustrated in Figures 6.3.2-2 (a) and (b). These figures also define the terms Llong and Lshort. As the ratio Lshort/Llong increases, the frame approaches the case shown in Figure 6.3.2-2(b) and hence, the effective length factor can be greater than one.

(a)

(b)

Figure 6.3.2-2 Frames with Diagonal Braces that intersect the Columns The stability of the frame is quite dependent on not only the relative axial and flexural stiffness of the members but also the details of the connections between the members. The axial stiffness at the connection in the direction of the braces is dependent on the details of the connection.

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6.3.2.3 Upright Frames with Diagonal Braces that Intersect Horizontal Braces are illustrated in Figures 6.3.2-3 (a) and (b). As the ratio Lshort/Llong increases, the basic behavior of the frame approaches that of Figure 6.3.2-3 (b) and hence the effective length factor can be greater than one.

(a)

(b)

Figure 6.3.2-3 Upright Frames with Diagonal Braces that intersect the Horizontal Braces 6.3.2.4 For uprights having bracing patterns such as the configuration shown in Figure 6.3.2-1 (b) no typical effective length factors are recommended. Rational analysis is to be used for such cases to determine the effective length factor. Alternately, the load carrying capacity may be determined by test. 6.3.3

Torsional Buckling Though torsional buckling is not likely to happen in rack structures, torsionalflexural buckling is usually the governing critical buckling mode. The torsional buckling effective length factor is a parameter in the analysis of torsional-flexural behavior. The provision of the Section 6.3.3 is based on References 14 and 22. The value of Kt given in this section assumes an effective connection between the columns and the braces as shown in Figure 6.3.3-1.

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Figure 6.3.3-1 Joint details 6.3.4

Diagonals and Horizontals The design procedures for upright frames in the cross-aisle, or transverse, direction should include the design detailing of the structural connections in those frames. Typically, the diagonal and horizontal framing members, often arranged in a truss-like configuration, frame into the front and rear columns of the frame, as well as into or onto one another. The framing members are members, of closed or open cross section, which are inserted into the open sections of the front and rear open column cross sections. The column channel sections may be some variation of C-sections, with and without stiffening legs, which may have, in turn, additional return stiffening elements to stiffen the reinforcing legs. There exist a large variety of combinations of horizontal and diagonal member cross sections, framing into and onto one another, and their various internal framing arrangements, framing into or onto column sections, and welded or bolted in a variety of patterns. Because of the large number of proprietary combinations, each manufacturer has a responsibility to provide the documentation of the adequacy of their connection designs to the Authority Having Jurisdiction. This documentation may take the form of a detailed analytical procedure demonstrating the adequacy of the joints within the context of Section 6.5.2 of FEMA 460[4]. Alternatively, the results of a testing protocol for the frames subjected to forces in the plane of the frames in the cross-aisle or transverse direction may be undertaken. The analysis and design of the upright frame joints (or connections) shall include a consideration of the transfer of the member forces into and through those joints along with their connections and the deformation of the member legs, lips, and stiffening elements that make up the cross section of the various members coming into each joint. It is recognized that under large forces caused by seismic loads, these joints will behave in a manner that allows inelastic deformation of 39

Commentary to ANSI MH16.1- 2012(R2019)

the members as well as their joints and distortion of their cross sections. Inelastic deformations that result from seismic demand contribute to the overall energy-absorbing and energy-dissipating structural behavior of the overall rack system, a mechanism that helps the rack systems to survive while continuing to carry their product loads. The detailed analysis of the members, because of the complex nature of those joints as described above, is often not amenable to rigorous analysis. Alternatively, a testing protocol discussed in Section 6.5.3 of FEMA 460 [4], based on the work of Krawinkler, may be undertaken to demonstrate the adequacy of the rack structural system, including all the members and their joints, subjected to transverse loadings. A report of the results of such tests shall provide the basis of the documentation of the adequacy, along with the stiffness and ductility of the connection joints. Joints of rack upright frames are complex, varied, often proprietary, and usually not amenable to rigorous stress analysis or structural analysis. Under static loading conditions, and particularly under dynamic or seismic loading conditions, the stiffness and ductility properties may enable structural performance into the nonlinear inelastic regions. These complex behaviors contribute to the energy-absorbing and energy-dissipating damping processes that allow rack structures to withstand the applied forces, dissipate energy without shedding their loads, and to survive the design-level earthquakes in order to carry their products safely for another day. The processes discussed here are the beginning of the development of performancebased design of such systems.

6.4 STABILITY OF TRUSSED-BRACED UPRIGHT FRAMES The provisions of this section are based on Reference 20 with the exception of the value of K. The expressions given in the reference were for members that have constant axial force throughout their entire length. The effective length factor K is intended to modify these expressions for the case of non-uniform distribution of axial forces. The provisions of this section are more likely to govern for high rise racks.

7 COLUMN BASE DESIGN 7.1 COLUMN BASE PLATES 7.1.1

Bearing on Concrete Formulas for determining the maximum permissible bearing stress (ASD) or load (LRFD) on the concrete floor are given in the specification. These resultant values may be used to design the column base plates unless the concrete floor designer requires a larger bearing area. The owner should ensure that the strength of the floor, including, but not limited to, the strength of the concrete, the thickness of the floor slab, the method of reinforcement, and the quality of the subgrade is adequate for the storage rack loading. For bearing surfaces other than concrete, special design is required.

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The Specification is for the design of storage racks only. Floor slab design is a separate issue not within the scope of the Specification. 7.1.2

Base Plate Design The column base connections must be designed to resist the forces and moments obtained from the structural analysis. Actual field experience and limited testing has shown that base plates thinner than those normally provided under hot rolled structural shapes, designed to AISC Specifications may be acceptable. Welds from the base plate to the column should be adequate to properly transfer all loads. When analysis indicates, the bearing plate and welds to the rack column shall be designed for uplift forces and/or bending moments. The owner shall bring special base plate considerations to the attention of the rack supplier. The Specification contains detailed methods for calculating the required thickness of the column base plates. Three load cases are considered: 1) downward vertical load; 2) uplift; and 3) axial load plus bending. For uplift ½ the distance from the nearest edge of the column to the anchor location reflects reverse curvature bending of the base plate. The provision to determine base plate thickness by load test has been retained from the previous editions without any change.

7.1.3

Maximum Considered Earthquake Base Rotation The rotational stiffness of the base is modeled in the down-aisle frame analysis as a rotational spring with stiffness Kb. The base moments, Mb, are determined from the structural analysis of the down-aisle model. The rotational demand of the base is Θ = Mb / Kb. The equation given for base demand amplifies this moment by multiplying it by Cd to increase Θ to the design earthquake level. If the analysis model does not take into account the amplified gravity load drift the 1+α factor is required as shown in the specification equation. Conversely, if the analysis takes into account the amplified gravity load drift, the 1+ α factor is not required because the effect has been already been accounted for. See Section 2.6.4 for discussion of the (1 +α) term. When the applied to the LRFD Mb should used.

ASD design method of analysis is used, the seismic forces that are the structure are only 67 percent of the forces that are applied using design method. To compensate for this difference the base moment be multiplied by 1.5 for computing Θb when the ASD design method is

The rotation stiffness and the rotational capacity can be determined by tests. 7.1.4

Shims Shims are commonly used to allow columns and uprights to be installed plumb and/or level and to transfer the column loads to the supporting concrete floor slab. Some operational conditions may result in the accidental displacement 41

Commentary to ANSI MH16.1- 2012(R2019)

and/or dislodgement of an improperly secured shim stack. The transfer of the column loads relies on the shim stack remaining in place. The integrity of the shim stack may be maintained by a variety of methods including, but not limited to, friction, nesting, interlocking, welding and/or multiple anchors. Shim stacks greater than six times the anchor diameter are not allowed and an alternate solution must be properly engineered. Shim stack heights between two and six times the anchor diameter must be secured so that through normal usage they are not dislodged. Shim stack heights less or equal to two times the anchor diameter are not required to be interlocked due to the decreased probability of dislodgement for these smaller shim stacks. A review of typical racks in high seismic configurations was performed to determine whether bending effects need be considered on the anchors when the shim stack heights are significant. This has shown that the horizontal seismic shear at the base of the rack is less than the static frictional force developed between shims and between the shims and the base plate. Therefore, it was concluded that anchor bending does not need to be considered in the seismic design of anchorage. For empty rack subjected to wind forces, bending of the anchors should be investigated if shim heights are expected to exceed a height equal to the anchor diameter.

7.2 SLAB AND SUBGRADE EVALUATION 7.3 ANCHOR BOLTS 7.3.1

Anchor Bolt Design The proper embedment of the anchor is critical to the design capacity of the anchor and the minimum required embedment must be achieved. Embedment of the anchor is the final measurement below the floor surface regardless of the base plate or shim, if used.

7.3.2

Periodic Inspection of Anchor Bolt Installation It may be required to conduct periodic inspection of the anchor bolt installation. The owner or the owner’s designated representative should seek an independent qualified inspector to carry out this inspection. When this inspection is needed, only those anchors that are part of the main force resisting system need to be inspected. This is because there are often accessories, not covered in the Specification, in and around the rack system that are not part of the main structural system. The following information is provided to offer some recommendations for this periodic inspection. These recommendations assume a concrete floor that is adequate to support the structure and is suitable for the anchor type being used. These recommendations are not mandatory.

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Periodic inspection may be waived for anchors that have calculated factored uplift using the LRFD method that is less than or equal to 1000 lbs. (454 kg) or 50% of the uplift capacity (when the uplift capacity is calculated using LRFD method). For the ASD method calculated uplift is less than 667 lbs. (303 kg) or 33 % of the uplift capacity (when the uplift capacity is calculated using ASD method). Periodic inspection is usually waived in Seismic Design Categories A, B or C. The Inspector shall deliver the required inspection report to the rack owner and other interested parties, in an acceptable format. The anchor bolt inspector shall be present prior to the installation of the anchors that require periodic inspection. The inspector shall verify that the installer of the anchors is installing the correct type and brand of anchor bolt that has been specified on the “Load and Rack Configuration” (LARC) drawings or the rack installation drawings. The inspector must also make sure that the installer has a copy of the manufacturer’s installation procedure for the anchor that is being installed. The inspector must visually inspect the anchor, the drill and bits that are to be used for the installation to make sure they are correct and compatible with the anchor being installed. He must make sure that the anchors provided are long enough to obtain the specified embedment shown on the LARC drawings for the case of the highest shim stack needed. The inspector must observe and approve the installation of the first several anchors at the base of the column or other member that is to be anchored. The installation is to be done per the manufacturer’s installation instructions and in accordance with the LARC drawings. The anchors are to be tightened to the anchor bolt manufacturer’s specifications. After the installation and approval of initial anchor bolt group, the anchor bolt inspector shall allow the installer to continue with the installation of anchor bolts. If there is more than one anchor bolt configuration, but the anchor size and type of anchor are the same, the actual inspection of the installation of the anchor bolt need not be repeated, but the other configurations (patterns) should be reviewed for compliance with the LARC drawings. If the anchor sizes change, the bits for each size should be reviewed for compatibility with the anchor. If there is more than one type of anchor used, the installation of each type shall be observed and approved following all of the steps above for each anchor type. Subsequent inspections may be done at any time but must be done when: ➢ There is a request to change the type of anchor that is used during a project. ➢ Changes in site conditions that may affect anchoring. Examples of this include rebar interference or proximity to floor joints or edges. When modifications to the installation of the anchor bolts are 43

Commentary to ANSI MH16.1- 2012(R2019)

necessary, a qualified engineer must review the modification and ensure that the change will result in adequate anchorage of the structural member. Intermediate inspections should be done on projects with over 1000 anchors. Intermediate inspections are only needed to ensure that the installer is continuing to properly install the anchor bolts, and that no new problems have been experienced since the initial inspection. Final anchor bolt inspection is required on all projects that require inspection. The inspector should make sure that all anchors have been installed in their correct locations per the LARC drawings and that the anchors have the correct embedment. The special inspection is over once all of the anchor bolts have been installed and the building official has accepted and approved the final inspection report.

8 SPECIAL RACK DESIGN PROVISIONS 8.1 OVERTURNING A very important aspect of rack design is to provide stability against overturning of the rack structure when the rack is subjected to horizontal forces. Horizontal forces on the rack structure can be due to wind (Section 2.5), earthquake (Section 2.6) or the force described in this section. The designer is cautioned not to consider the stabilizing forces provided by ordinary anchorage to maintain rack alignment. However, if forces on anchors are analyzed and the anchors designed for these forces with appropriate safety factors, then the anchorage forces may be considered in the stability analysis. A limit on the height to depth ratio of the rack is imposed. This ratio is defined as the height to the topmost loaded beam divided by the frame width (or the combined width of interconnected frames). While it is recommended that all frames be anchored (Section 1.4.7), here it states that if the 6 to 1 ratio is exceeded, the rack must be analyzed for overturning even in the absence of seismic and wind forces. A 350 pound (159 kg) lateral force, which could result from moving equipment servicing the rack, is applied at the topmost shelf level for the purpose of designing the anchorage. This short duration load need not be considered in the design of the column. A further limit on the height to depth ratio is given as 8 to 1. Stabilizing a single row of rack that exceeds this ratio with floor anchors alone is not recommended. Under certain circumstances, this may be feasible, but such cases should be thoroughly analyzed and certified by a qualified design professional. The provisions of this section apply to frames of constant depth over their height. Other configurations such as offset or sloped legs require more detailed analysis.

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8.2 CONNECTIONS TO BUILDINGS The relative stiffness of racks and buildings vary significantly. Therefore, any attachment between the rack and the building shall be made with provisions for vertical and lateral building movements. Such attachments shall be proportioned so that the attachment would fail prior to causing damage to the building structure. Care should be taken that roof loads are not transferred to the racks.

8.3 INTERACTION WITH BUILDINGS This section recognizes that building structures and rack structures are likely to have different structural characteristics. During an earthquake, this could have a magnifying effect for structures that are interconnected but which have differing periods of vibration. Thus, the connections must be designed to ensure that neither structure causes damage to the other during a seismic event.

8.4 PICK MODULES AND RACK SUPPORTED PLATFORMS Pick modules are found in warehouse and distribution centers and allow rapid throughput of product. They are customized multi-level racks that support one or more product storage bays having a fork truck aisle on one side and a pick aisle floor on the opposite side. Pallets or products are generally inserted into a product storage bay from fork trucks on the fork truck aisle side, and removed by workers from the pick aisle side. The pallets may either be stationary in the product storage bay or may flow toward the pick aisle floor. Most pick modules are frame-beam style racks with integrated pick module walkways or platform levels that are used by authorized or trained order picking personnel for the loading and unloading of products. These structures are intended to be in an industrial distribution environment and are not open to the general public. Pick modules are free standing structures within a warehouse. The pick module walkways have flooring, guardrails, stairways, and often have conveyor systems that deliver and/or remove products. These structures should be designed using the provisions of the Specification. This section is intended to provide special provisions for these structures that are needed in addition to the requirements of the rest of the Specification. Rack-supported platforms have elevated platforms like pick modules, but the platforms may be more wide open and involve other activities in addition to order picking. 8.4.1

Posting of Design Loads The design loads for a rack-supported platform or pick module walkway should be on the rack configuration and load application drawings. The design loads should also be posted on the structure and serve as a reminder to the users of the load limit for the pick module walkway or rack-supported platform.

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8.4.2

Design Requirements The minimum pick module walkway design live load of 60 psf (293 kg/m2) is given to support the order picking personnel. The user should advise the designer if there are to be such activities or equipment on the pick module floor that would require a higher design load. Also, the conveyor live and product loads, dead loads and any other equipment or fixtures that are on the platform floor should be considered (such as lighting, sprinkler piping, etc). When the project specifications require a design live load of more than 100 psf (488 kg/m2) and there are two or more elevated floor levels, the Specification allows the designer to reduce the live load by 20 percent for the design of the support framing. The support framing includes the columns, the frame bracing, the frame bracing connections and the base plates. It does not include the platform support beams and their connections. It would be excessively conservative to require the columns (and support structure members) to be sized for all of the floor levels having all of the live loads present at the same time. This reduction only applies to the floor live load for the walkway areas. It does not apply to other loads such as dead loads or product loads. A tighter limit on live load beam deflection is required for floor supporting beams because the L/180 limit used for rack beams may result in too much deflection and could cause the floor to “bounce”. For this reason a rack manufacturer’s beam tables should not be used to select beams for platforms without proper consideration of deflection. The deflection from the total load may not exceed L/180. The designer may limit the total deflection to L/240 or check the deflection separately for both cases. A 30” (762 mm) minimum clear pick aisle walkway width is recommended to allow the order pickers the clearance to safely navigate the walkway and perform the picking operations.

8.4.3

Rack-Supported Platform and Pick Module Guards Since pick modules and rack-supported platforms involve order picking personnel on elevated platforms or walkways, adequate safety systems that provide fall protection for the workers must be in place and properly designed. The purpose of this section is to provide the requirements for the pick module guardrail and handrail systems and also the safety decking system, if required. These are the most common systems used to provide fall protection on pick module structures. These systems are not intended to serve as a substitute for proper training and proper conduct of the workers who use these structures. These systems are intended to provide reasonable protection for workers who are working in accordance with the safety procedures to which they have been trained.

8.4.3.1

Guardrail Requirements Because these are specialized structures that are not open to the general public and intended to be used by authorized or trained personnel, guardrails may be used instead of handrail systems for fall protection. On the stair assembly, however, handrail systems are to be provided. On stairways, the top guardrail 46

Commentary to ANSI MH16.1- 2012(R2019)

may serve as a handrail if it meets all of the design requirements of a handrail. Handrails are not required on stair landings but guardrails must be used to provide 42 inches (1066 mm) high fall protection on the stair landing. Intermediate landings that are provided in a straight continuous stairway may use handrail or guardrail. Kick-plates are required where the guardrails are used. They may also be required at additional places as required and specified by the owner, such as under the charge side of floor-level carton flow shelves that are raised off the floor to create pitch. Often kick-plates are not required at edges because there may be an adjacent deck or structural element that would prevent product from sliding off the edge of the floor. Many modules are designed to have static pallet drop-off locations on the elevated floor levels of the module. Where these are used, the floor must be properly designed for the load weights and a gate, removable section of guardrail or removable chains must be used. These gates or removable guardrails or chains must be secured at all times, except when a load is being picked up or deposited at the pallet drop location. Proper safety precautions must be adhered to at all times when opening and closing the guardrail section, gate or chains at the pallet drop-off location and when removing or depositing the loads. When removable chains are used, the chains may not have excessive slack if they are to provide safe fall protection. For this reason, a limit has been placed on the sag of chains. An intermediate chain must also be used as is required for guardrail systems. Kickplates are required where removable handrails or chains are used for the purpose of providing a load drop-off point where the loads are being placed into the module. Because of the nature and use of these structures, some exceptions to normal practice for guardrail and kick plate are needed. These exceptions are provided to avoid situations where guardrail or kick plates, etc. could actually create obstacles to the use of the structure, which could prove to be hazards rather than safety enhancements. However, care must be taken in the design to ensure that the occupants of the structure are safe when they are properly using the pick module or rack-supported platform. 8.4.3.2

Safety Flooring Requirements The Pick modules often contain product flow lanes. Because loads can sometimes hang up or not flow freely, safety flooring is recommended or required. Safety flooring is designed by the flooring manufacturer with the following specifications: 300 lbs(136 kg) concentrated load (to support the picker), Dynamic distributed load of 60 psf (293 kg/m2) acting separately, and Any other issues necessary to protect both the picker and pick module. Order pickers should have proper training and should follow the safety procedures that are established for stepping onto this safety flooring. An example of this procedure may be that the pickers should not walk on the outermost safety flooring load positions where they could fall from the module. The Specification limits this distance to 4 feet. These procedures will vary 47

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depending on the configuration of the structure and the working environment. It is not the purpose of the Specification to establish the exact procedures, as they may vary, but rather to stress the importance of having safety procedures that are strictly followed. Under no circumstances should a picker climb or walk into the rack when safety flooring has not been provided for that purpose. 8.4.4

Stairways The requirements for stairs in this section are intended to match the stairway requirements common to stairways that are required for an industrial environment. Building codes will often have requirements for stairways that are more stringent than those outlined in this section, because such requirements are intended for stairways that are open to the general public. Handrail systems are required for stairways. The handrail system may be guardrail if the top rail of the guardrail system meets the same requirements as a stairway handrail. Stair handrail extensions are not needed on module structures and can actually be obstacles to swift orderly egress during an emergency situation. This section recommends that stair handrail extensions not be used.

8.4.5

Product Fall Protection There also may need to be systems in place to protect areas within or around the structure from products that could accidentally fall. These locations may be areas where people could be, or areas where falling product could cause other types of property damage or safety hazards. These areas should be identified by the owner and brought to the attention of the designer and the proper barriers, if required, should be supplied and installed. These requirements will vary depending on the products, the operation and the configuration of the structure.

8.5 AUTOMATED STORAGE AND RETRIEVAL SYSTEMS An automated storage and retrieval system (stacker rack) is a structure commonly classified as a special industrial occupancy category.

9 TEST METHODS 9.1 GENERAL Many factors affecting the design of rack are difficult to account for analytically. Section 9 spells out a series of optional tests that may be used to evaluate the effects of components on the overall behavior. Except as either modified or supplemented in the Specification, AISI [1] and AISC [3] Specifications shall apply to the testing of components. The engineers involved in rack design are probably familiar with the test procedures stipulated in the Specification. However, some comments bear reiterating here. The important factor that must be kept in mind is that a test procedure should be such

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that the test results are repeatable. Anyone using the same test procedure on the same specimen should arrive at the same results. It is also important that tensile coupons be taken from each specimen to determine the actual yield stress. Generally, the actual yield stress of the steel is higher than the specified minimum yield stress. It is important to know the actual yield stress in order to analyze the test results. It is also essential to have a complete report spelling out test procedures, the results and the analysis of the results.

9.2 STUB COLUMN TESTS FOR COLD-FORMED AND HOT-ROLLED COLUMNS Because of the interplay of three influences, which affect a cold-formed perforated compression member, (i.e., local buckling, perforations, and cold-work of forming) recourse must be taken to determination by tests. This is done by stub column tests, (i.e., by careful concentric compression testing of pieces of the member short enough so as not to be affected by column buckling). The details of such testing are spelled out in Part VIII of the AISI Cold-Formed Steel Design Manual [2]. 9.2.1

Test Specimen and Procedure

9.2.2

Evaluation of Test Results Q is a factor used in Sections 4.1.2 and 4.1.3. The column formulas, as well as the test determination of Q, utilize the yield strength of the material. It is, therefore, essential that the value of Fy used in the column formulas be connected with the yield strength Fy used when determining Q. This is elaborated below. The basic definition of Q is:

Q=

actual strength of stub column hypothetical maximum strength without weakening influences

In turn, this hypothetical strength in the case of nonperforated sections, is Afull Fy. For shapes Q<1 the AISI Specification [1] permits the cold-working in the flats to be utilized, but not that of the corners. For perforated members, the Specification assumes the hypothetical maximum strength to be governed by the minimum net section Anet min of a plane appropriately passed through the perforations. Correspondingly, Q is defined as:

Q=

ultimate strength of stub column Fy A net min

In regard to the yield strength, Fy, to be used by determining Q by test, and the value Fy for calculating the strength of columns according to AISI Specification [1] Section C4, the following needs attention. In calculating column strength according to AISI Specification [1] Section C4, Fy is the specified minimum yield strength to which the steel is ordered by the fabricator. On the other hand, the yield strength of the particular coil or sheet from which the stub column test 49

Commentary to ANSI MH16.1- 2012(R2019)

specimens will have been made, will be different and in general somewhat larger than the ordered minimum yield point. In order for the determination of Q to be adequately accurate, it is necessary that the virgin yield point of the stub column test material (before forming) be as close as possible to the specified strength; it should not deviate from it by more than -10% to +20%. With this proviso, the Specification in conjunction with the quoted AISI Specification [1] Appendix A5.2.2 allows the determination of Fy in the formula for calculating Q and consistent values of Fy for calculating column strength according to the AISI Specification [1] Section C4. For a series of columns having different thicknesses, the thickest and the thinnest may be tested. For any intermediate thickness, the Q so determined should be used in column strength calculations according to the AISI Specification [1] Section C4 in conjunction with a value Q obtained by similar interpolation. That is,

Q = Q min +

(Q max − Q min )(t − t min ) (t max − t min )

where Qmin is for the stub column with the thickness tmin, Qmax is for the stub column with thickness tmax, both determined as above. (Note that Qmin is not the smaller of the two Q-values, but the Q-value for the stub column of the smaller thickness.) This method is adequately accurate only if the actual virgin yield strengths of the two stub columns with tmax and tmin are not too different. For this reason the Specification limits this difference to 25%. It is acceptable to linearly interpolate the Q-values for a series of shapes with identical cross-section and perforation dimensions, but with a variety of thicknesses. For this purpose Qmax and Qmin should be determined from stub column tests on specimens made with the maximum and minimum thicknesses of coil from which the stub column was made. This correction is necessary in order to avoid unsafe design in case the virgin yield stress (before forming) of the specimens was significantly higher than the specified minimum. By the procedures above, it is possible to obtain Q-values larger than 1 (one). This is so if the neglected strengthening effects of cold-work outweigh the weakening effects of the perforations. However, it is basic to the use of Q in the AISI Specification [1] that it can only be equal to or smaller than, but not larger than 1.0. Correspondingly, the Specifications provide that if the selected procedure for determining Q results in a Q-value larger than 1.0, Q = 1.0 shall be used.

9.3 PALLET BEAM TESTS In this section, depending on the information required, two different types of tests are specified, (i.e. simply-supported pallet beam tests and pallet beam in upright frame assembly.)

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The loading in these tests is applied by means of a test machine or jacks. This loading may restrain the torsional distortions and hence, may lead to unconservative results for members subject to such distortions. The beam test methods illustrated do not account for impact. However, in practice, test results will have to be adjusted to consider the added impact effect. 9.3.1

Simply-Supported Pallet Beam Tests This test can also be used in the design of beams, in general, when the end restraint is deemed not to lead to significant increase in the load carrying capacity. In the determination and yield moments, the number of tests needed shall be determined according to the AISI Specification [1].

9.3.1.1

Test Setup The test setup illustrated in Figure 9.3.1-1 shall be used.

Figure 9.3.1-1 Simply-Supported Pallet Beam Tests. The value of C shown in the figure above shall be between 2.5 and 3 and has been chosen to avoid shear failure and to ensure a sufficiently long portion with constant moment. For most pallet beams, the end connection detail is such that the beam can be placed directly on the supporting surface and have simply supported end conditions. In this case, the clamps, diaphragms of stiffeners at the supports most likely will not be needed. 9.3.1.2

Test Procedure General guidelines given in Section 9.1.3 shall be used in addition to the particular requirements specified herein.

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9.3.2

Pallet Beam in Upright Frames Assembly Tests This test is intended to simulate the conditions in the actual rack as close as possible to determine the allowable load. This test may also be used to determine the magnitude of the joint spring constant F defined in the commentary to Section 9.4. For vertical loads this test may reflect the actual behavior of the connections more accurately than the test described in Section 9.4.1.

9.3.2.1

Test Setup It is specified that the upright frame not be bolted to the floor even if the actual racks are. The test is intended to represent the behavior of the rack between the inflection points. Therefore, any restraint at the column bases other than due to the pressure should be avoided. It is important to minimize friction between beams and pallets because new, dry pallets on new, dry beams, when used in the test, could provide considerably more bracing than pallets and beams worn smooth in use and possibly covered with a film of oil.

9.3.2.2

Test Procedure

9.3.2.3

Evaluation of Test Results General guidelines given in Section 9.1.3 shall be used in addition to the following three particular requirements or criteria for determining allowable load. The first of these is the determination of the factor of safety or the resistance factor according to Section F of the AISI Specification. The second criterion by which to determine allowable loads from the test results prescribes a safety factor of 1.5 against excessive load distortion.

9.3.2.4

Number of Tests Required

9.3.2.5

Deflection Test The third and last criterion limits deflection of beams under design load to 1/180 of the span. To satisfy this requirement, the load that results in this amount of deflection should be read from the load deflection curve plotted from the test results. If this load is smaller than those obtained from the first two requirements, it governs.

9.4 PALLET BEAM-TO-COLUMN CONNECTION TESTS The tests specified in this section have two objectives. One is to determine the moment capacity of the connection, and the other is the determination of the joint spring constant F described below for use with the rational analysis approach. In a rigid frame analysis the members connected in a joint are assumed to maintain the angle between themselves, while the frame deflects under the applied loading. The joints between the upright columns and the pallet beam, in general, are not rigid. 52

Commentary to ANSI MH16.1- 2012(R2019)

This is primarily due to the distortion of the walls of the columns at the joint, and to a lesser extent, due to the distortion taking place at the connectors themselves. This peculiarity influences the overall behavior very significantly. The connection details vary widely. Thus, it is impossible to establish general procedures for computing joint stiffness and strength. It is, therefore, necessary to determine these characteristics by simple test. The change in angle between the column and the connecting beam  (in radius) can be idealized as follows:

θ=

M F

where M is the moment at the joint between connecting members and F is the spring constant relating the moment to the rotation. 9.4.1

The Cantilever Test The Cantilever Test provides a simple means of determining the connection moment capacity and rigidity. However, it has the disadvantage that the ratio of shear force (that is the vertical reaction) to moment at the joint is not well represented. For typical rack connections this ratio is probably higher than it is in the cantilever test as spelled out in the Specification. In general, a higher ratio would probably lead to a more rigid connection. However, bending moment and shear force would interact and lower the ultimate load of the connection. This effect should be studied by reducing the length of the cantilever to the distance between the end of the beam and the expected location of the inflection point. This test is suitable for determining F for computing stresses due to vertical loads. A somewhat more tedious, but more accurate determination of F, can be achieved by tests according to Section 9.3.2.

9.4.1.1

Test Setup This test setup illustrated in Figure 9.4.1.1-1:

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Figure 9.4.1.1-1 Cantilever Test 9.4.1.2

Evaluation of Test Results The relationship between the moment and the angular change at a joint is not linear. The following equation appears to be reasonable for determining a constant value of F to be used in a linear analysis:

F=

( R.F.) δ0.85 L L - c - b 2 P0.85 L b 16EIc 3EIb

where P0.85 is 0.85 times the ultimate load and 0.85 is the deflection of the free end of the cantilever at load P0.85, Lc, Lb, Ic, Ib are the same lengths and moments of inertias of the columns and the beam, respectively. (R.F.) is a reduction factor to provide safety considering scatter of test results. Since a lower F means a higher design moment for the beam, an (R.F.) = 2/3 should be included in the design of the beam. However, in determining bending moments for the columns, a higher F leads to a more conservative value of the bending moment. It is, therefore, recommended to take (R.F.) = 1.0 for this case. It is suggested that the spring constant, F, be calculated on the basis of the average results on two tests of identical specimens provided that the deviation from the average results of two tests does not exceed 10%. If the deviation from the average exceeds 10%, then a third specimen is to be tested. The average of the two higher values is to be regarded as the result in the design of the columns. 9.4.2

The Portal Test The portal test is desirable when the value of F obtained is to be used in a sidesway analysis either for lateral deflections or stability. Under vertical loads the connections, in general, “tighten up”. Subsequently, under sidesway, the connection at one end of the beam “tightens up”, while the connection at the 54

Commentary to ANSI MH16.1- 2012(R2019)

other end “loosens.” The portal test gives an approximate average value of the spring constants involved in the process. Thus, it is more desirable to use the portal test for evaluating sidesway behavior, namely, the effective lengths and horizontal deflections. 9.4.2.1

Test Setup A schematic of the test setup is shown in the Figure 9.4.2.1-1. According to the Specification, h = 24 in (61 cm). Dial gage #1 shall be used to measure the lateral deflection, , of the rack. Dial gages #2 and #3 indicate whether the column bases are properly restrained or not. In lieu of dial gages, other deflection measuring devices may be used. In general, the friction between concrete and the half round bars is enough for this restraint.

Figure 9.4.2.1-1 Portal test 9.4.2.2

Test Procedure

9.4.2.3

Evaluation of Test Results The following is a possible rational analysis for evaluating test results . Considering a portal height, h, and span, L, with moments of inertia of the columns and beams designated Ic and Ib respectively, and expression for maximum sidesway deflection, , corresponding to a lateral load of 2H combination as follows: =

Hh 3 Hh 2L Hh 2 + + 3EI c 6EIb F

Solving this equation for F, the following is obtained:

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F=

R.F. δ h L 2 − − 2 Hh 3EI c 6EI b

R.F. is a reduction factor that should be taken equal to 2/3. E=

the modulus of elasticity.

h=

the distance from the floor to top of the beam.

H=

the horizontal load per beam.

Ib = floor.

the moment of inertia of the beam about the axis parallel with the

Ic = the moment of inertia of the column about the axis parallel with the upright frame. L= the distance between the centroid of the two columns parallel with the shelf beam. =

Sway deflection corresponding to a lateral load of 2H.

Since the behavior at both the design load and the ultimate load is of interest, portal tests are to be conducted at both load levels. Multiple tests, as recommended in the commentary on Section 9.4.1.3, are also recommended here.

9.5 UPRIGHT FRAME TEST The hazard of collapse of a full scale high rise rack system poses severe safety problems. Therefore, the testing procedures proposed herein are geared to a reduced scale that will, by simulating a full scale test, establish the upright frame capacity in a safe manner. The tests are further intended to simulate the conditions in the actual racks as closely as possible. Test Setup for Horizontal Load in the Direction Perpendicular to the Upright Frame:

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Figure 9.5.1.1.1-1 Test Setup

9.6 CYCLIC TESTING OF BEAM-TO-COLUMN CONNECTIONS 9.6.1

General There has been much concern written or otherwise expressed by some members of the structural engineering community in the last several decades about rack structural behavior. However, the rack industry, through the Rack Manufacturers Institute, has worked long and hard with and through the various model code organizations, with the BSSC, with the ASCE, with the ICC and with the NFPA to have its products be covered rigorously but fairly by existing and evolving design provisions as applied to building-like Nonbuilding Structures. It is known that rack structural systems that have been designed, permitted through a codeenforcement process, manufactured, installed, and utilized in accordance with applicable RMI provisions, have performed well in recent seismic events. Storage rack structural systems are presently designed in accordance with the Rack Manufacturers Institute Specification for the Design, Testing, and Utilization of Industrial Steel Storage Racks, along with the added provisions of NEHRP [7] Section 14.3.5, ASCE 7 [6] Section 9.6.2.9, and IBC [8] Section 2208. The consequence of the added provisions as they appear in the NEHRP, ASCE, and IBC is to cause an upper limit or cap to be imposed on the period of rack structural behavior under seismic conditions. In turn, this causes artificially large base shear forces to be predicted in the resulting structural analysis, since the seismic behavior of racks during a strong earthquake had not been rationally explained. The imposition of inordinately large base shear forces has been the requirement since the early 1970’s, when the UBC first introduced provisions to be applied to seismic behavior of steel storage rack. The current cap that results from current 57

Commentary to ANSI MH16.1- 2012(R2019)

provisions imposes an upper limit of 0.6 seconds on the period of the rack structural response where it is well known that typical storage rack may have periods of 2 to 4 seconds in the longitudinal direction. Further, it is well known that rack periods, rack damping, and overall rack structural behavior is very dependent on the beam-to-column connectors and connections and their moment-rotation characteristics that are the key and integral component of rack structures. The testing procedures in this section are analogous to those in the AISC Provisions although the rotational demands and associated capacities can be several times larger in high seismic areas than those required in the AISC Provisions because of the much higher drifts typical of storage racks.

9.6.2

Definitions The following definitions shall characterize the test set-up and the conduct of the test: Complete Loading Cycle - A cycle of rotation taken from zero force to zero force, including one positive and one negative peak. Drift Angle - Displacement divided by height, radians. Inelastic Rotation - The permanent or plastic portion of the rotation angle between a beam and a column of the Test Specimen, measured in radians. The Inelastic Rotation shall be computed based on an analysis of the Test Specimen deformations. Sources of inelastic rotation include yielding of members, yielding of connection elements and connectors, and slip between members and connection elements. For beam-to-column moment connections in Moment Frames, inelastic rotation shall be computed based upon the assumption that inelastic action is concentrated at a single point located at the intersection of the centerline of the beam with the centerline of the column. Prototype - The connections, member sizes, steel properties, and other design, detailing, and construction features to be used in the actual storage rack frames. Test Specimen - A portion of a frame used for laboratory testing, intended to model the prototype. Test Setup - The supporting fixtures, loading equipment, and lateral bracing used to support the load and Test Specimen. Test Subassemblage - The combination of the Test Specimen and pertinent portions of the Test Setup.

9.6.3

Test Subassemblage Requirements The Test Subassemblage shall replicate, as closely as is practicable, the conditions that will occur in the Prototype during earthquake loading. The Test Subassemblage shall include the following features:

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(1) The Test Specimen shall consist of at least a single column element with beam segments attached to both sides of the column. (2) Points of inflection in the test subassemblage shall coincide approximately with the anticipated points of inflection in the prototype under earthquake loading. (3) Lateral bracing of the test subassemblage is permitted near load application or reaction points as needed to provide lateral stability of the Test Subassemblage. Additional lateral bracing of the Test Subassemblage is not permitted, unless it replicates bracing to be used in the Prototype.

Figure 9.6.3-1 Test Setup

9.6.4

Essential Test Variables The Test Specimen shall replicate as closely, as is practicable, the pertinent design, detailing, and construction features, and the material properties of the Prototype. The following variables shall be replicated in the Test Specimen:

9.6.4.1

Sources of Inelastic Rotation Inelastic Rotation shall be developed in the Test Specimen by inelastic action in the same members and connection elements as anticipated in the prototype, i.e., in the beam, in the column, in the panel zone, or within the connection elements. The fraction of the total Inelastic Rotation in the Test Specimen that is developed in each member or connection element shall be at least seventy-five percent of the anticipated fraction of the total Inelastic Rotation in the Prototype that is developed in the corresponding member or connection element.

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9.6.4.2

Size of Members The size of the beams used in the Test Specimen shall be representative of typical full-size storage rack beams. The size of the columns used in the Test Specimen shall be representative of typical full-size storage rack columns, and shall properly represent the inelastic action in the column, as defined in Section 9.6.3 (1). Extrapolation beyond the limitations stated in this section shall be permitted subject to qualified peer review and approval by the Authority Having Jurisdiction.

9.6.4.3

Connection Details The beam-to-column connectors, and the connection details used in the Test Specimen, shall represent the typical full-sized connection details as closely as possible. The connection elements used in the Test Specimen shall be representative of typical full-size storage rack connectors and connection details.

9.6.4.4

Material Strength The following additional requirements shall be satisfied for each member of the connection element of the Test Specimen that contributes to Inelastic Rotation at yielding. (a) The yield stress shall be determined by material tests on the actual materials used for the Test Specimen, as specified in the Section below on Materials Testing. Because of the amount of cold-working to which the connector is subjected in manufacture and testing, the yield stress for connectors will be determined from connectors taken from identical neighboring components in the manufacturing sequence. The use of yield stress values that are reported on certified mill test reports are not permitted to be used for purposes of this Section. (b) The yield stress of the beam shall not be more than 15 percent below RyFy for the grade of steel to be used for the corresponding elements of the Prototype. Columns, connectors, and connector elements with a tested yield stress shall not be more than 15 percent above or below RyFy for the grade of steel to be used for the corresponding elements of the Prototype. RyFy shall be determined in accordance with Section 6.2 of AISC Seismic [23]. Here, Fy is the minimum specified yield strength; and Ry is the ratio of the expected yield strength to the minimum expected yield strength Fy.

9.6.4.5

Welds Welds on the Test Specimen shall satisfy, and be performed in strict conformance, with the requirements of the Welding Procedure Specifications (WPS) as required.

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9.6.4.6

Bolts The bolted portions of the Test Specimen shall replicate the bolted portions of the Prototype connection as closely as possible. (a) The bolt grade used in the Test Specimen shall be the same as that used for the Prototype. (b) The type and orientation of bolt holes used in the Test Specimen shall be the same as those to be used for the corresponding bolt holes in the Prototype. (c) When inelastic rotation is to be developed either by yielding, or by slip within a bolted portion of the connection, the method used to make the bolt holes in the Test Specimen shall be the same as that used in the corresponding bolt holes in the prototype. (d) Bolts in the Test Specimen shall have the same installation and faying surface preparation as that used for the corresponding bolts in the Prototype.

9.6.5

Testing Procedure Section 9.4 of the RMI Specification presents a testing and evaluation protocol intended to evaluate the characteristics of typical rack beam-to-column connections. These tests are to be executed on behalf of each storage rack manufacturer in order to determine and evaluate the moment/rotation stiffnesses and their limiting values for their various beam-to-column connectors. This testing protocol is based on FEMA 350 Table 3-14 scaled up by a factor appropriate for rack beam-to-column connectors, These characteristics, when evaluated in a dependable and reproducible manner by an independent testing laboratory, will then become the basis for the removal or modification of the present cap on rack structural period. A more reasonable period value will be used to calculate a more reasonable prediction of rack structural behavior, including drift, which is more representative of the response of real systems in the field under seismic conditions. Typical rack behavior will be tested with beam-to-column rotations of up to 0.1 radians, with up to five cycles, and will be representative of rack structures having displacements resulting in drift of h/50. Following the last cycle of the cyclic tests, the moment/rotation behavior will be recorded to failure where the rotation will be on the order of 0.3 radians. Rack beam-to-column connectors normally exhibit a large degree of ductility in response to demand placed on such connections. For example, assuming a drift index of 0.02 (h/50), which is about the most ever seen on a shake table, the demand rotation would be 0.04 radians. This is because shake tables have not had the displacement capacity to test actual earthquake motions in the 2 to 4 second period range. However, rack connections can achieve failure rotations of 0.2 to 0.3 radians, some ten times the drift index. Comparing this to a building structure, the UBC [9] requires that joints accommodate a drift of 0.0025 at 0.03 radians for a ductile frame, and around 0.015 for an “ordinary” moment frame, which is six times the building drift. Rack connections generally exhibit more ductility than any representative building connection. This capacity is needed 61

Commentary to ANSI MH16.1- 2012(R2019)

since demand on rack connections is many times the demand on building structural connections, so it is quite possible for a rack connection with a capacity of 0.10 radians to be inadequate. The FEMA/AISC testing protocol requires a large number of cycles leading up to approximately 0.03 radians, where 1 to 3 cycles are needed. For a rack beamto-column connection, such a large number of cycles could be excessive. Thus, to cut down on testing time, it is proposed that connections be cycled as shown in Commentary Section 9.6.6.1. The testing program should include tests of at least two specimens of each combination of beam and column and connector size. The results of the tests should be capable of predicting the median value of drift angle capacity for the performance states described below. The drift angle limits θ for various performance levels shall be defined as indicated in the following figure.

9.6.6 9.6.6.1

Performance Level

Symbol

Drift Angle Capacity

Strength degradation

θSD

Taken as the value of θ, from the following Figure, at which either failure of the connection occurs or the strength of either connection degrades to less than the nominal capacity, whichever is less.

Ultimate

θU

Taken as the value of θ, from the following Figure, at which connection damage is so severe that continued ability to remain stable under gravity loading is uncertain.

Loading History General Requirements Prior to the application of any cyclic loading, a constant downward load, Pc, of one kip shall be applied to each beam segment adjacent to each connector on both sides of the beam-to-column connection simulating the design downwardacting gravity pallet loads that serve to fully engage the beams and their connectors into the columns receiving them. Loading will proceed with the application of equal displacements at each end of each beam, and the measurement of the force corresponding to each such displacement. Thus, the testing setup and apparatus requires the use of two independent actuators to measure the two different forces being developed at the two beam-ends, where equal displacement are being applied. The Test Specimen shall be subjected to cyclic loads according to the requirements prescribed for beam-to-column moment connections in Moment

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Frames. Loading sequences, other than those specified here, may be used when they are demonstrated to be of equivalent or greater severity. Loading Sequence for Storage-Rack Beam-to-Column Connections Qualifying cyclic tests of storage-rack beam-to-column connections shall be conducted by controlling the peak Drift Angle, θ, imposed on the Test Specimen as follows: Load Step # (1) (2) (3) (4) (5) (6)

3 cycles at 3 cycles at 3 cycles at 3 cycles at 2 cycles at 2 cycles at

θ θ θ θ θ θ

= = = = = =

0.025 radians 0.050 radians 0.075 radians 0.100 radians 0.150 radians 0.200 radians

Continue loading at increments of θ = 0.050 radians, with two cycles of loading at each step. 9.6.7

Instrumentation Sufficient instrumentation shall be provided on the Test Specimen to permit measurement or calculation of the quantities listed in the Section on Test Reporting Requirements that follows.

9.6.8 9.6.8.1

Material Testing Requirements Tension Testing Requirements Tension testing shall be conducted on samples of steel taken from the material adjacent to each Test Specimen. Tension-test results from certified mill test reports shall be reported, but are not permitted to be used in place of specimen testing for the purposes of this Section. Tension-test results shall be based upon testing that is conducted in accordance with the Section on Methods of Tension Testing. Tension testing shall be conducted and reported for the following portions of the Test Specimen: (a) Flange(s) and web(s) of beams and columns at standard locations. (b) Any element of the connector that contributes to inelastic rotation by yielding.

9.6.8.2

Methods of Tension Testing Tension testing shall be conducted in accordance with the appropriate ASTM testing protocols for the particular materials being used, with the following exceptions: (a) The yield stress, Fy, that is reported from the test shall be based upon the yield strength definition in ASTM A370, using the offset method at 0.002 strain.

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(b) The loading rate for the tension test shall replicate, as closely as practicable, the loading rate to be used in the Test Specimen. 9.6.9

Test Reporting Requirements For each Test Specimen, a written test report meeting the requirements of the Authority having jurisdiction, and the requirements of this Section, shall be prepared. Some of these items may come from the manufacturer of the sample and others from the testing laboratory. The report shall thoroughly document all key features and results of the test. The report shall include the following information: (1) A drawing or clear description of the Test Subassemblage, including key dimensions, boundary conditions at loading and reaction points, and location of any lateral braces. (2) A drawing of the connector and connection details, showing member sizes, grades of steel, the sizes of all connector and connection elements, welding details including any filler metals, the sizes and locations of any slots or bolt holes, the size and grade of bolts, and all other pertinent details, of the connection. (3) A listing of all other Essential Variables for the Test Specimen, as listed in the Section on Essential Test Variables. (4) A listing or plot showing the applied load and displacement history of the Test Specimen. (5)

A plot of the applied load versus the displacement of the Test Specimen. The displacement reported in this plot shall be measured at or near the point of load application. The locations on the Test Specimen, where the loads and displacements were measured, shall be clearly identified.

(6)

A plot of Beam Moment versus Drift Angle for beam-to-column moment connections. For beam-to-column connections, the beam moment and the Drift Angle shall be computed with respect to the centerline of the column.

(7) The Drift Angle and the total Inelastic Rotation developed by the Test Specimen. The components of the Test Specimen, contributing to the total Inelastic Rotation due to yielding or slip, shall be identified. The portion of the total Inelastic Rotation contributed by each component of the Test Specimen shall be reported. The method used to compute Inelastic Rotations shall be clearly shown. (8)

A chronological listing of significant test observations, including observations of yielding, slip, instability, tearing, and fracture of any portion of the Test Specimen, as applicable.

(9) The controlling failure mode for the Test Specimen. If the test is terminated prior to failure, the reason for terminating the test shall be clearly indicated. 64

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(10) The results of the material tests specified under Material Testing Requirements, above. (11) The Welding Procedure Specifications (WPS) and welding inspection reports. Additional drawings, data, photographs, and discussion of the Test Specimen or test results are permitted to be included in the report. 9.6.10 Acceptance Criteria The Test Specimen must satisfy the Strength and Drift Angle requirements of this protocol for the connection, as applicable. The Test Specimen must sustain the required Drift Angle for at least one complete loading cycle. The test results will also include the beam-to-column moment-rotation characteristics and “dynamic spring relationship” for each of the combinations tested. Thus, a process is presented herein by which the structural beam-to-column connections will be evaluated by series of tests conducted by an independent testing laboratory. While many of the rack manufacturers use cold-formed lightgauge structural sections for their rack structural systems; the procedure presented herein is equally applicable to systems employing hot-rolled sections. The intent of this proposal, in the absence of other provisions, is to apply and mimic the test procedures which have developed for connection behavior of hotrolled structural sections as articulated in FEMA 350 [24], AISC Seismic Provisions [23], ATC 19 (1995) [25], ATC 24 [26], and the SEAOC Blue Book (1999). 9.6.11 Evaluation of Test Results The tests specified in this section are to be used to determine that moment strength and inelastic rotational capacity of the beam-column connection. The tests are also used to determine the rotational stiffness properties of the connection. These properties are determined as follows: 1. The test values of PL and PR are summed for each value of Δ tested. 2. The average moment M, at each Δ, is ( PL + PR) * ℓ/2 3. The rotational angle θ, at each Δ, is Δ/ℓ 4. Plot M versus θ for each Δ tested 5. The Maximum Value of Mmax is the Maximum Moment and the Maximum Rotational Capacity θmax is the lowest value of θ where the Maximum Moment occurs. The value of Mmax needed to have been sustained for 2 cycles. 6. For LRFD design the Design Moment Strength is ΦMmax , where Φ is 0.9. 7. For ASD design the Design Moment Strength is Mmax/Ω, where Ω is 1.67. 8. The Rotational Stiffness should be determined based on the calculated Moment, M, for the design loads from the analysis using the plot of M versus θ. For example, for the calculated design moment, M, one would 65

Commentary to ANSI MH16.1- 2012(R2019)

go to the plot for M and determine the corresponding θ. The rotational stiffness would be M/θ. Since the calculated period and design forces depend on the stiffness, the value of M depends on θ. This means determining the appropriate rotational stiffness is an iterative process.

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10 REFERENCES 1. AISI (2007), North American Specification for the Design of Cold-Formed Steel Structural Members. American Iron and Steel Institute, Washington, DC, 2007 Edition. 2. Cold-Formed Steel Design Manual, American Iron and Steel Institute, Washington, DC, 2008 Edition 3. AISC (2010), Specification for Structural Steel Buildings, ANSI/AISC 360-10 An American National Standard, American Institute of Steel Construction, Chicago, Ill, June 22, 2010 4. AISC. Manual of Steel Construction, 14th ed. Chicago: American Institute of Steel Construction, March 2011 5. Seismic Considerations for Steel Storage Racks located in Areas Accessible to the Public, FEMA 460, September 2005 6. Minimum Design Loads for Buildings and Other Structures, American Society of Civil Engineers, ASCE/SEI 7-10 7. BSSC. NEHRP (National Earthquake Hazards Reduction Program) Recommended Provisions for the Development of Seismic Regulations for New Buildings. Washington, DC: Building Seismic Safety Council, Federal Emergency Management Agency, 2009 8. IBC International Building Code, International Code Council – 2012 9. UBC. Uniform Building Code. Whittier, CA: International Conference of Building Officials, 1997 10. BOCA. National Building Code. Building Officials and Code Administrators International, 1996 11. SBC. Standard Building Code. Southern Building Code Congress International, 1997 12. Davies, J. M., "Down-Aisle Stability of Rack Structures," Proceedings of the Eleventh Specialty Conference on Cold-Formed Steel Structures, St. Louis, Missouri, October 20-21, 1992. 13. Pekoz, Teoman, ‘Development of a Unified Approach to Design of ColdFormed Steel Members’, AISI Report S.G.-86-4, November 1986. 14. Pekoz, Teoman, ‘Design of Perforated Cold-Formed Steel Columns’ Proceeding of 9th International Specialty Conference, Cold-Formed Steel Structures, St. Louis, MO, November 1988. 15. Pekoz, T. and Winter, G. “Torsional-Flexural Buckling of Thin-Walled Sections under Eccentric Loading,” J. of the Structural Division, ASCE, May 1969 16. Galambos T. V. (Editor), "Guide to Stability Design Criteria for Metal Structures," Fifth Edition, John Wiley and Sons, New York, NY, 1998

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Commentary to ANSI MH16.1- 2012(R2019)

17. Galambos, T. V., “Influence of Base Fixity on Frame Stability,” Journal. of the Structural Division, ASCE, May 1960. 18. Salmon, C. G., Schelenker, L. and Johnston, B. G. “Moment Rotation Characteristics of Column Anchorages”, Proceedings, ASCE, April 1955. 19. Chajes, A, Fang, P. J. and Winter, G. “Torsional-Flexural Buckling, Elastic and Inelastic of Cold-Formed Steel Thin Walled Columns”, Cornell Engineering Research Bulletin, 1966, Ithaca, N. Y. 20. Timoshenko, S. P. and Gere, J. M. “Theory of Elastic Stability”, McGraw-Hill Book Company, New York, NY, Second Edition 21. ”Effective Length and Notional Load Approaches for Assessing Frame Stability: Implications for American Steel Design” ASCE 1997 22. “Cold-Formed Steel Frame and Beam-Column Design Final Report” by Andrew Sarawit available from http://ceeserver.cee.cornell.edu/tp26/TWResearchGroup/research%20reports. htm 23. Seismic Provisions for Structural Steel Buildings, ANSI/AISC 341-10 An American National Standard, American Institute of Steel Construction, Chicago, Ill, March 9, 2005 24. Recommended Seismic Design Criteria for New Steel Moment-Frame Buildings, FEMA 350, Federal Emergency Management Agency, July 2000. 25. Structural Response Modification Factors, ATC 19, Applied Technology Council, 1995. 26. Guidelines for Cyclic Seismic Testing of Components of Steel Structures, ATC 24, Applied Technology Council, 1992. 27. ACI 318 (2011) Building Code Requirements for Structural Concrete Appendix D (2011 Edition) 28. Quantification of Building Seismic Performance Factors, FEMA P695, June 2009

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