1、14Steel Design Guide SeriesStaggered Truss Framing Systems14Steel Design GuideStaggered Truss Framing SystemsNeil Wexler, PEWexler Associates Consulting EngineersNew York, NYFeng-Bao Lin, PhD, PEPolytechnic UniversityBrooklyn, NYAMERICAN INSTITUTE OF STEEL CONSTRUCTIONfront matter D814.qxd 12/18/200
2、2 9:47 AM Page 1Copyright 2001byAmerican 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 in this publication has been prepared in accordance withrecogniz
3、ed engineering principles and is for general information only. While it isbelieved to be accurate, this information should not be used or relied upon for any spe-cific application without competent professional examination and verification of itsaccuracy, suitablility, and applicability by a license
4、d professional engineer, designer, orarchitect. The publication of the material contained herein is not intended as a rep-resentation or warranty on the part of the American Institute of Steel Constructionor of any other person named herein, that this information is suitable for any general orpartic
5、ular use or of freedom from infringement of any patent or patents. Anyone mak-ing use of this information assumes all liability arising from such use.Caution must be exercised when relying upon other specifications and codes devel-oped by other bodies and incorporated by reference herein since such
6、material maybe modified or amended from time to time subsequent to the printing of this edi-tion. The Institute bears no responsibility for such material other than to refer to it andincorporate it by reference at the time of the initial publication of this edition.Printed in the United States of Am
7、ericaFirst Printing: December 2001Second Printing: December 2002Revised: October 2003Revised: November 2009front matter D814:front matter D814.qxd 11/16/2009 10:59 AM Page 2vNeil Wexler, PE is the president of Wexler Associates, 225East 47thStreet, New York, NY 10017-2129, Tel:212.486.7355. He has a
8、 Bachelors degree in Civil Engi-neering from McGill University (1979), a Masters degreein Engineering from City University of New York (1984);and he is a PhD candidate with Polytechnic University, NewYork, NY. He has designed more then 1,000 building struc-tures.Feng-Bao Lin, PhD, PE is a professor
9、of Civil Engineeringof Polytechnic University and a consultant with WexlerAssociates. He has a Bachelors degree in Civil Engineer-ing from National Taiwan University (1976), Mastersdegree in Structural Engineering (1982), and PhD in Struc-tural Mechanics from Northwestern University (1987).In recent
10、 years staggered truss steel framing has seen anationwide renaissance. The system, which was developedat MIT in the 1960s under the sponsorship of the U.S. SteelCorporation, has many advantages over conventional fram-ing, and when designed in combination with precast con-crete plank or similar floor
11、s, it results in a floor-to-floorheight approximately equal to flat plate construction. Between 1997 and 2000, the authors had the privilege todesign six separate staggered truss building projects. Whileresearching the topic, the authors realized that there was lit-tle or no written material availab
12、le on the subject. Simulta-neously, the AISC Task Force on Shallow Floor Systemsrecognized the benefits of staggered trusses over other sys-tems and generously sponsored the development of thisdesign guide. This design guide, thus, summarizes theresearch work and the practical experience gathered.Ge
13、nerally, in staggered-truss buildings, trusses are nor-mally one-story deep and located in the demising wallsbetween rooms, with a Vierendeel panel at the corridors.The trusses are prefabricated in the shop and then bolted inthe field to the columns. Spandrel girders are bolted to thecolumns and fie
14、ld welded to the concrete plank. The exte-rior walls are supported on the spandrel girders as in con-ventional framing.Staggered trusses provide excellent lateral bracing. Formid-rise buildings, there is little material increase in stag-gered trusses for resisting lateral loads because the trussesar
15、e very efficient as part of lateral load resisting systems.Thus, staggered trusses represent an exciting and new steelapplication for residential facilities. This design guide is written for structural engineers whohave building design experience. It is recommended that thereaders become familiar wi
16、th the material content of the ref-erences listed in this design guide prior to attempting a firststructural design. The design guide is written to help thedesigner calculate the initial member loads and to performapproximate hand calculations, which is a requisite for theselection of first member s
17、izes and the final computeranalyses and verification.Chapter 7 on Fire Resistance was written by Esther Slub-ski and Jonathan Stark from the firm of Perkins EastmanArchitects. Section 5.1 on Seismic Strength and DuctilityRequirements was written by Robert McNamara from thefirm of McNamara Salvia, In
18、c. Consulting StructuralEngineers.AUTHORSPREFACEfront matter D814.qxd 12/18/2002 9:47 AM Page vviThe authors would like to thank the members of the AISCStaggered Truss Design Guide Review Group for theirreview, commentary and assistance in the development ofthis design guide:J. Steven AngellMichael
19、L. BaltayAine M. BrazilCharles J. CarterThomas A. FaraoneRichard A. Henige, Jr.Socrates A. IoannidesStanley D. LindseyRobert J. McNamaraRobert W. PyleKurt D. SwenssonTheir comments and suggestions have enriched thisdesign guide. Special thanks go to Robert McNamara fromMcNamara Salvia, Inc. Consulti
20、ng Engineers, who wroteSection 5.1 Strength and Ductility Design Requirements.Bobs extensive experience and knowledge of structuraldesign and analysis techniques was invaluable. Also thanksto Esther Slubski who wrote Chapter 7 on Fireproofing.Special thanks also go to Marc Gross from the firm ofBren
21、nan Beer Gorman Architects, Oliver Wilhelm fromCybul only spandrel columns exist. There are interiorcolumns on conventionally framed bents.Moment frames are used along the long direction of thebuilding, while staggered trusses and moment frames areused in the short direction.Two different truss type
22、s are shown on the plan, namelytrusses T1 and T2. Fig. 1.5 shows truss T1B and Fig. 1.6shows truss T2C. Truss T1B is Truss Type 1 located on gridline B, and T2C is Truss Type 2 located on grid line C. Thetruss layout is always Truss Type 1 next to Type 2 to mini-mize the potential for staggered trus
23、s layout errors. Eachtruss is shown in elevation in order to identify member sizesand special conditions, such as Vierendeel panels. Any spe-cial forces or reactions can be shown on the elevationswhere they occur. The structural steel fabricator/detailer isprovided with an explicit drawing for piece
24、-mark identifi-cation. Camber requirements should also be shown on theelevations.Table 1.2 shows the lateral forces calculated for thebuilding. For this building, which is located in a low-seis-mic zone, wind loads on the wide direction are larger thanseismic forces, and seismic forces are larger in
25、 the narrowdirection. So that no special detailing for seismic forceswould be required, a seismic response modification factor Rof 3 was used in the seismic force calculations. The distrib-uted gravity loads of the building are listed below, whereplate loads are used for camber calculations. Dead Lo
26、ads10” precast hollow core plank 75 psfLeveling compound 5 Structural steel 5 Partitions 12 Dead Loads 97 psfPlate Loads10” precast hollow core plank 75 psfStructural steel 5 Plate Loads 80 psfLive Loads 40 psfWall LoadsBrick 40 psfStuds 3Sheet rock 3Insulation 2 Wall Loads 48 psfThe loads listed ab
27、ove are used in the calculations thatfollow.1.4 ResponsibilitiesThe responsibilities of the various parties to the contract arenormally as given on the AISC Code of Standard Practicefor Steel Buildings and Bridges. All special conditionsshould be explicitly shown on the structural drawings.Fig. 1.4
28、Typical floor framing plan. Note: * indicates moment connections.Chapter 1 D814.qxd 12/18/2002 10:24 AM Page 341.5 Design MethodologyThe design of a staggered-truss frame is done in stages.After a general framing layout is completed, gravity, wind,and seismic loads are established. Manual calculatio
29、ns andmember sizing normally precede the final computer analy-sis and review. For manual calculations, gravity and lateralloads are needed and the member sizes are then obtainedthrough vertical tabulation.The design methodology presented in this design guide isintended to save time by solving a typi
30、cal truss only oncefor gravity loads and lateral loads, then using coefficients toobtain forces for all other trusses. The method of coeffi-cients is suitable for staggered trusses because of the repe-tition of the truss geometry and because of the “racking” orshearing behavior of trusses under late
31、ral loads. This is sim-ilar to normalizing the results to the “design truss”.Approximate analysis of structures is needed even intodays high-tech computer world. At least three significantreasons are noted for the need for preliminary analysis asfollowing:1. It provides the basis for selecting preli
32、minary membersizes, which are needed for final computer input andverification.2. It provides a first method for computing differentdesigns and selecting the preferred one.3. It provides an independent method for checking thereports from a computer output.Theoretically, staggered-truss frames are tre
33、ated as struc-turally determinate, pin-jointed frames. As such, it isassumed that no moment is transmitted between membersacross the joints. However, the chords of staggered trussesare continuous members that do transmit moment, andsome moment is always transmitted through the connec-tions of the we
34、b members.The typical staggered-truss geometry is that of a “Pratttruss” with diagonal members intentionally arranged to bein tension when gravity loads are applied. Other geometries,however, may be possible.1.6 Design PresentationThe structural drawings normally include floor framingplans, structur
35、al sections, and details. Also, structural notesand specifications are part of the contract documents. Floorplans include truss and column layout, stairs and elevators,dimensions, beams, girders and columns, floor openings,section and detail marks. A column schedule indicates col-umn loads, column s
36、izes, location of column splices, andsizes of column base plates.The diaphragm plan and its chord forces and shear con-nectors with the corresponding forces must be shown. It isalso important that the plan clearly indicate what items arethe responsibilities of the steel fabricator or the plank man-u
37、facturer. Coordination between the two contractors is crit-ical, particularly for such details as weld plate location overstiffeners, plank camber, plank bearing supports, and clear-ances for stud welding. Coordination meetings can be par-ticularly helpful at the shop drawing phase to properlylocate
38、 plank embedded items.In seismic areas, the drawings must also indicate theBuilding Category, Seismic Zone, Soil Seismic Factor,Importance Factor, required value of R, and Lateral LoadResisting System.Table 1.2 Wind and Seismic Forces (All Loads are Service Loads) WIND (ON WIDE DIRECTION) SEISMIC (B
39、OTH DIRECTIONS) Lateral Load Story Shear hLateral Load Service Story Shear hFloor Vj(kips) Vw(kips) (%) Vj (kips) Vw (kips) (%) Roof 107 107 9% 83 83 13% 12 105 212 18% 90 173 26% 11 103 315 27% 82 255 39% 10 103 418 36% 78 333 51% 9 103 521 45% 65 398 61% 8 98 619 54% 58 456 70% 7 96 715 62% 52 508
40、 78% 6 93 808 70% 44 552 85% 5 91 899 78% 39 591 91% 4 86 985 86% 29 620 95% 3 84 1069 93% 21 641 98% 2 79 1148 100% 11 652 100% Ground Chapter 1 D814.qxd 12/18/2002 10:24 AM Page 45Fig. 1.5 Staggered truss type T1B. Note: indicates number of composite studs (” dia., 6” long, equally spaced).Chapter
41、 1 D814.qxd 12/18/2002 10:24 AM Page 56Fig. 1.6 Staggered truss type T2C. Note: indicates number of composite studs (” dia., 6” long, equally spaced).Chapter 1 D814.qxd 12/18/2002 10:24 AM Page 672.1 General InformationIt is advisable to start the hand calculations for a staggered-truss building wit
42、h the design of the diaphragms. In a stag-gered-truss building, the diaphragms function significantlydifferent from diaphragms in other buildings because theyreceive the lateral loads from the staggered trusses andtransmit them from truss to truss. The design issues in ahollow-core diaphragm are sti
43、ffness, strength, and ductility,as well as the design of the connections required to unloadthe lateral forces from the diaphragm to the lateral-resistingelements. The PCI Manual for the Design of Hollow CoreSlabs (PCI, 1998) provides basic design criteria for plankfloors and diaphragms.Some elements
44、 of the diaphragm design may be dele-gated to the hollow core slab supplier. However, only theengineer of record is in the position to know all the param-eters involved in generating the lateral loads. If any designresponsibility is delegated to the plank supplier, the locationand magnitude of the l
45、ateral loads applied to the diaphragmand the location and magnitude of forces to be transmittedto lateral-resisting elements must be specified. An additional consideration in detailing diaphragms isthe need for structural integrity. ACI 318 Section 16.5 pro-vides the minimum requirements to satisfy
46、structuralintegrity. The fundamental requirement is to provide a com-plete load path from any point in a structure to the founda-tion. In staggered-truss buildings all the lateral loads aretransferred from truss to truss at each floor. The integrity ofeach floor diaphragm is therefore significant in
47、 the lateralload resistance of the staggered-truss building. 2.2 Distribution of Lateral ForcesThe distribution of lateral forces to the trusses is a struc-turally indeterminate problem, which means that deforma-tion compatibility must be considered. Concretediaphragms are generally considered to be
48、 rigid. Analysisof flexible diaphragms is more complex than that of rigiddiaphragms. However, for most common buildings subjectto wind forces and low-seismic risk areas, the assumption ofrigid diaphragms is reasonable. If flexible diaphragms areto be analyzed, the use of computer programs with plate
49、-element options is recommended.For the example shown in this design guide, a rigiddiaphragm is assumed for the purpose of hand calculationsand for simplicity. This assumption remains acceptable aslong as the diaphragm lateral deformations are appropri-ately limited. One way to ensure this is to limit thediaphragm aspect ratio and by detailing it such that itremains elastic under applied loads. From Smith and Coull(1991), the lateral loads are distributed by the diaphragm totrusses as follows:Vi= Vs+ VTORS(2-1)whereVi= truss shear due to lateral loadsVs=
