1、Steel Design Guide SeriesErection Bracingof Low-Rise Structural Steel BuildingsCopyright 1997byAmerican Institute of Steel Construction, Inc.All rights reserved. This book or any part thereofmust not be reproduced in any form without thewritten permission of the publisher.The information presented i
2、n this publication has been prepared in accordance with rec-ognized engineering principles and is for general information only. While it is believedto be accurate, this information should not be used or relied upon for any specific appli-cation without competent professional examination and verifica
3、tion of its accuracy,suitablility, and applicability by a licensed professional engineer, designer, or architect.The publication of the material contained herein is not intended as a representationor warranty on the part of the American Institute of Steel Construction or of any otherperson named her
4、ein, that this information is suitable for any general or particular useor of freedom from infringement of any patent or patents. Anyone making use of thisinformation assumes all liability arising from such use.Caution must be exercised when relying upon other specifications and codes developedby ot
5、her bodies and incorporated by reference herein since such material may be mod-ified or amended from time to time subsequent to the printing of this edition. TheInstitute bears no responsibility for such material other than to refer to it and incorporateit by reference at the time of the initial pub
6、lication of this edition.Printed in the United States of America Revision: October 2003 2003 by American Institute of Steel Construction, Inc. All rights reserved.This publication or any part thereof must not be reproduced in any form without permission of the publisher.TABLE OF CONTENTSERECTION BRA
7、CING OFLOW RISE STRUCTURALSTEEL BUILDINGS1. INTRODUCTION 11.1 Types of Systems . 11.2 Current State of the Art 11.3 Common Fallacies 21.4 Use of This Guide 2PART 1DETERMINATION OF BRACINGREQUIREMENTS BY CALCULA-TION2. INTRODUCTION TO PART 1 . 23. CONSTRUCTION PHASE LOADSFOR TEMPORARY SUPPORTS . 23.1
8、 Gravity Loads . 33.2 Environmental Loads . 33.2.1 Wind Loads . 33.2.2 Seismic Loads . 43.3 Stability Loads . 73.4 Erection Operation Loads 73.5 Load Combinations . 74. RESISTANCE TO CONSTRUCTIONPHASE LOADS BY THE PERMANENTSTRUCTURE 84.1 Columns . 104.2 Column Bases 114.2.1 Fracture of the Fillet We
9、ld Connectingthe Column to the Base Plate . 114.2.2 Bending Failure of the Base Plate 134.2.3 Rupture of Anchor Rods . 154.2.4 Buckling of the Anchor Rods . 154.2.5 Anchor Rod Pull or Push Through . 164.2.6 Anchor Rod Pull Out 164.2.7 Anchor Rod “Push Out“ of theBottom of the Footing . 174.2.8 Pier
10、Bending Failure 184.2.9 Footing Over Turning . 184.3 Tie Members . 244.3.1 Wide Flange Beams 244.3.2 Steel Joists . 254.3.3 Joist Girders 264.4 Use of Permanent Bracing . 264.5 Beam to Column Connections 274.6 Diaphragms 275. RESISTANCE TO DESIGN LOADS -TEMPORARY SUPPORTS . 275.1 Wire Rope Diagonal
11、Bracing 285.2 Wire Rope Connections . 345.2.1 Projecting Plate . 345.2.2 Bent Attachment Plate 355.2.3 Anchor Rods . 365.3 Design of Deadmen 395.3.1 Surface Deadmen 395.3.2 Short DeadmenNear Ground Surface . 39PART 2DETERMINATION OF BRACINGREQUIREMENTS USING PRE-SCRIPTIVE REQUIREMENTS6. INTRODUCTION
12、 TO PART 2 417. PRESCRIPTIVE REQUIREMENTS . 417.1 Prescriptive Requirements for the PermanentConstruction . 417.2 Prescriptive Requirements for Erection Sequenceand Diagonal Bracing 42REFERENCES . 59Acknowledgements 60APPENDIX 61 2003 by American Institute of Steel Construction, Inc. All rights rese
13、rved.This publication or any part thereof must not be reproduced in any form without permission of the publisher.ERECTION BRACING OFLOW RISE STRUCTURALSTEEL BUILDINGS1. INTRODUCTIONThis guide is written to provide useful informationand design examples relative to the design of temporarylateral suppo
14、rt systems and components for low-risebuildings. For the purpose of this presentation, low-risebuildings are taken to have the following characteris-tics:(1) Function: general purpose structures for suchuses as light manufacturing, crane buildings,warehousing, offices, and other commercialand instit
15、utional buildings.(2) Proportions:(a) height: 60 feet tall or less.(b) stories: a maximum of two stories.Temporary support systems are required whenever anelement or assembly is not or has not reached a state ofcompletion so that it is stable and/or of adequatestrength to support its self-weight and
16、 imposed loads.The need for temporary supports is identified in Para-graph M4.2 of the AISC Specification for StructuralSteel Buildings and in Section 7 of the AISC Code ofStandard Practice for Steel Buildings and Bridges.To a great extent the need for this guide on tempo-rary supports was created b
17、y the nature and practice ofdesign and construction of low-rise buildings. In manyinstances, for example, the lateral bracing systems forlow-rise buildings contain elements which are not in thescope of the steel erectors work. For this reason theCode of Standard Practice makes a distinction betweenS
18、elf-Supporting and Non-Self-Supporting frameworkas will be discussed later. Other temporary supportssuch as shoring and cribbing for vertical loads are notincluded in the scope of this guide.1.1 Types of SystemsLateral bracing systems for low-rise buildings canbe differentiated as follows:Braced con
19、struction: In this type of system, truss-like bays are formed in vertical and horizontalplanes by adding diagonals in vertical baysbounded by columns and struts or in horizontal baysbounded by beams and girders. In general, bracedconstruction would be characterized as self-sup-porting, however, the
20、frames may contain elementssuch as a roof deck diaphragm which would changethe frame to a non-self-supporting type.Rigid Frame Construction: This system uses mo-ment resisting joints between horizontal and verti-cal framing members to resist lateral loads by frameaction. In many buildings the rigid
21、frames are dis-cretely located within the construction to minimizethe number of more costly moment resisting con-nections. The remainder of the frame would havesimple connections and the frame would be de-signed to transfer the lateral load to the rigidframes. Rigid frame construction would also bec
22、haracterized as self-supporting, however in thecase of braced construction the framework maycontain non-structural elements in the systemwhich would make it a non-self-supporting frame.Diaphragm Construction: This system uses hori-zontal and/or vertical diaphragms to resist lateralloads. As stated a
23、bove horizontal diaphragms maybe used with other bracing systems. Horizontal di-aphragms are usually fluted steel deck or a concreteslab cast on steel deck. Vertical diaphragms arecalled shear walls and may be constructed of cast-in-place concrete, tilt-up concrete panels, precastconcrete panels or
24、masonry. Vertical diaphragmshave also been built using steel plate or fluted wallpanel. In most instances, the elements of dia-phragm construction would be identified as non-self-supporting frames.Cantilever Construction: Also called Flag PoleConstruction, this system achieves lateral load re-sistan
25、ce by means of moment resisting base con-nections to the foundations. This system wouldlikely be characterized as self-supporting unlessthe base design required post erection grouting toachieve its design strength. Since grouting is usual-ly outside the erectors scope, a design requiringgrout would
26、be non-self-supporting.Each of the four bracing systems poses different is-sues for their erection and temporary support, but theyshare one thing in common. All as presented in the proj-ect Construction Documents are designed as completesystems and thus all, with the possible exception of Can-tileve
27、r Construction, will likely require some sort oftemporary support during erection. Non-self-support-ing structures will require temporary support of theerection by definition.1.2 Current State of the ArtIn high-rise construction and bridge constructionthe need for predetermined erection procedures a
28、ndtemporary support systems has long been established inthe industry. Low-rise construction does not commanda comparable respect or attention because of the lowheights and relatively simple framing involved. Alsothe structures are relatively lightly loaded and the fram-1 2003 by American Institute o
29、f Steel Construction, Inc. All rights reserved.This publication or any part thereof must not be reproduced in any form without permission of the publisher.ing members are relatively light. This has lead to a num-ber of common fallacies which are supported by anec-dotal evidence.1.3 Common Fallacies1
30、. Low-Rise frames do not need bracing. In fact,steel frames need bracing. This fallacy is probably acarryover from the era when steel frames were primarilyused in heavy framing which was connected in substan-tial ways such as riveted connections.2. Once the deck is in place the structure is stable.I
31、n fact, the steel deck diaphragm is only one componentof a complete system. This fallacy obviously is the re-sult of a misunderstanding of the function of horizontaldiaphragms versus vertical bracing and may have re-sulted in the usefulness of diaphragms being oversold.3. Anchor rods and footings ar
32、e adequate for erec-tion loads without evaluation. In fact, there are manycases in which the loads on anchor rods and footingsmay be greater during erection than the loads imposedby the completed structure.4. Bracing can be removed at any time. In fact, thetemporary supports are an integral part of
33、the frame-work until it is completed and self-supporting. Thiscondition may not even occur until some time after theerection work is complete as in the case of non-self-supporting structures.5. The beams and tie joists are adequate as strutswithout evaluation. In fact, during erection strut forcesar
34、e applied to many members which are laterally bracedflexural members in the completed construction. Theiraxially loaded, unbraced condition must be evaluatedindependently.6. Plumbing up cables are adequate as bracingcables. In fact, such cables may be used as part of tem-porary lateral supports. How
35、ever, as this guide demon-strates additional temporary support cables will likelybe needed in most situations. Plumbing a structure is asmuch an art as a science. It involves continual adjust-ment commonly done using diagonal cables. The sizeand number of cables for each purpose are determinedby dif
36、ferent means. For example, the lateral supportcables would likely have a symmetrical pattern whereasthe plumbing up cables may all go in one direction todraw the frame back to plumb.7. Welding joist bottom chord extensions producesfull bracing. In fact, the joist bottom chords may be acomponent of a
37、 bracing system and thus welding themwould be appropriate. However, other components maybe lacking and thus temporary supports would be need-ed to complete the system. If the joists have not beendesigned in anticipation of continuity, then the bottomchords must not be welded.8. Column bases may be g
38、routed at any convenienttime in the construction process. In fact, until the col-umn bases are grouted, the weight of the framework andany loads upon it must be borne by the anchor rods andleveling nuts or shims. These elements have a finitestrength. The timing of grouting of bases must be coor-dina
39、ted between the erector and the general contractor.1.4 Use of This GuideThis guide can be used to determine the require-ments for temporary supports to resist lateral forces, i.e.stability, wind and seismic. The guide is divided intotwo parts. Part 1 presents a method by which the tempo-rary support
40、s may be determined by calculation of loadsand calculation of resistance. Part 2 presents a series ofprescriptive requirements for the structure and the tem-porary supports, which if met, eliminate the need to pre-pare calculations. The prescriptive requirements of Part2 are based on calculations pr
41、epared using the principlespresented in Part 1.PART 1DETERMINATION OF BRACINGREQUIREMENTS BY CALCULA-TION METHOD2. INTRODUCTION TO PART 1Part 1 consists of three sections. The first deals withdesign loads which would be applicable to the condi-tions in which the steel framework exists during thecons
42、truction period and specifically during the periodfrom the initiation of the steel erection to the removal ofthe temporary supports. Sections 4 and 5 deal with thedetermination of resistances, both of permanent struc-ture as it is being erected and of any additional tempo-rary supports which may be
43、needed to complete the tem-porary support system. An appendix is also presentedwhich provides tabulated resistances to various compo-nents of the permanent structure. This appendix followsthe reference section at the end of the guide.3. CONSTRUCTION PHASE LOADSFOR TEMPORARY SUPPORTSThe design loads
44、for temporary supports can begrouped as follows:Gravity loadsDead loads on the structure itselfSuperimposed dead loadsLive loads and other loads from constructionoperations2 2003 by American Institute of Steel Construction, Inc. All rights reserved.This publication or any part thereof must not be re
45、produced in any form without permission of the publisher.Environmental loadsWindSeismicStability loadsErection operationLoads from erection apparatusImpact loads caused by erection equipmentand pieces being raised within the structure3.1 Gravity LoadsGravity loads for the design of temporary support
46、sconsist of the self-weight of the structure itself, the self-weight of any materials supported by the structure andthe loads from workers and their equipment. Self-weights of materials are characterized as dead loads.Superimposed loads from workers and tools would becharacterized as live loads. Gra
47、vity loads can be distrib-uted or concentrated. Distributed loads can be linear,such as the weight of steel framing members, non-uni-form such as concrete slabs of varying thicknesses oruniform such as a concrete slab of constant thickness.Dead loads can be determined using the unit densityand unit
48、weights provided in the AISC Manual of SteelConstruction, (LRFD Part 7, ASD Part 6) and ASCE7-93, Tables Cl and C2. Dead loads can also be ob-tained from manufacturers and suppliers.Live loads due to workers and their equipmentshould be considered in the strength evaluation of par-tially completed w
49、ork such as connections or beamswhich are unbraced. The live load used should reflectthe actual intensity of activity and weight of equipment.In general, live loads on the order of 20 psf to 50 psf willcover most conditions.3.2 Environmental LoadsThe two principal environmental loads affectingthe design of temporary supports are wind and seismicloads. Other environmental loads such as accumulatedsnow or rain water may influence the evaluation of par-tially completed construction but these considerationsare beyond the scope of this guide.3.2.1 Wind LoadsWind loads on a structure are the
