AISC DESIGN GUIDE 5-1991 Low-and Medium-Rise Steel Buildings.pdf

1、Steel Design Guide SeriesLow-and Medium-RiseSteel BuildingsLow- andMedium-RiseSteel BuildingsDesign Guide for Low- and Medium-Rise Steel BuildingsHoratio Allison, PEConsulting EngineerDagsboro, DelawareAMERICAN INSTITUTE OF STEEL CONSTRUCTIONSteel Design Guide Series 2003 by American Institute of St

2、eel Construction, Inc. All rights reserved.This publication or any part thereof must not be reproduced in any form without permission of the publisher.Copyright 1991byAmerican Institute of Steel Construction, Inc.All rights reserved. This book or any part thereofmust not be reproduced in any form wi

3、thout thewritten permission of the publisher.The information presented in 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 speci

4、fic appli-cation without competent professional examination and verification 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

5、American Institute of Steel Construction or of any otherperson named herein, 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 e

6、xercised when relying upon other specifications and codes developedby other 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 r

7、efer to it and incorporateit by reference at the time of the initial publication of this edition.Printed in the United States of AmericaSecond Printing: October 2003 2003 by American Institute of Steel Construction, Inc. All rights reserved.This publication or any part thereof must not be reproduced

8、 in any form without permission of the publisher.TABLE OF CONTENTSBASIC DESIGN RULES FOR ECONOMY .LIVE LOAD AND BAY SIZE SELECTION Live Load Selection Bay Size SelectionCOMPOSITE FLOORS Allowable Stress (ASD) and LoadResistance Factor Design (LRFD) .Economy with LRFD .Floor Load Capacity Enhancement

9、Shored vs. Unshored Construction.Serviceability Considerations .Underfloor Duct Systems OPEN WEB JOIST FLOOR SYSTEMS Joist Size and Spacing Girder Beam Design Composite Joist Systems.Floor Vibration WIND LOAD DESIGN.Drift Limits .“K“ Bracing Frame Unbraced Frame Design .Special Wind Frames .APPENDIC

10、ES LRFD Composite Beam Design.Composite Beam Load Capacity Enhancement Composite Beam Long Term Deflection Steel Joist Typical Bay K-Frame Bracing Optimization .Unbraced Frame Design .iii112255667881010101011121213151723232529313336 2003 by American Institute of Steel Construction, Inc. All rights r

11、eserved.This publication or any part thereof must not be reproduced in any form without permission of the publisher.PREFACEThis booklet was prepared under the direction of the Com-mittee on Research of the American Institute of Steel Con-struction, Inc. as part of a series of publications on special

12、topics related to fabricated structural steel. Its purpose is toserve as a supplemental reference to the AISC Manual ofSteel Construction to assist practicing engineers engaged inbuilding design.The design guidelines suggested by the author that are out-side the scope of the AISC Specifications or C

13、ode do notrepresent an official position of the Institute and are not in-tended to exclude other design methods and procedures. Itis recognized that the design of structures is within the scopeof expertise of a competent licensed structural engineer,architect, or other licensed professional for the

14、applicationof principles to a particular structure.The sponsorship of this publication by the American Ironand Steel Institute is gratefully acknowledged.ivThe information presented in this publication has been prepared in accordance with recognized engineer-ing principles and is for general informa

15、tion only. While it is believed to be accurate, this information shouldnot be used or relied upon for any specific application without competent professional examination and verifi-cation of its accuracy, suitability, and applicability by a licensed professional engineer, designer, or archi-tect. Th

16、e publication of the material contained herein is not intended as a representation or warranty onthe part of the American Institute of Steel Construction, Inc. or the American Iron and Steel Institute, orof any other person named herein, that this information is suitable for any general or particula

17、r use or offreedom from infringement of any patent or patents. Anyone making use of this information assumes all lia-bility arising from such use. 2003 by American Institute of Steel Construction, Inc. All rights reserved.This publication or any part thereof must not be reproduced in any form withou

18、t permission of the publisher.DESIGN OF LOW- AND MEDIUM-RISE STEEL BUILDINGSBASIC DESIGN RULES FOR ECONOMYA few basic design rules for economy will be presentedherein. These rules should be considered in the conceptualphase in the design of a project. There are, of course, manyother considerations,

19、but these suggestions are simple andcan help in producing a good economical design.The cost of a filler beam and/or girder beam simply con-sists of the cost of the mill material, the cost of fabrication,and the cost of erection. The cost of fabrication and erec-tion for a single beam is essentially

20、the same for a heavybeam or a light beam. The real savings for a light membercompared to a heavier one is simply the difference in thecost of the mill material. Thus, beams should be spaced asfar apart as practical to reduce the number of pieces whichmust be fabricated and erected.Rigid moment conne

21、ctions and special connections forbracing are expensive. Care should be taken to minimize thenumber of these types of connections in a projectthat is,reduce the number of moment resisting and braced bents tothe minimum. Where practical, one may consider the use ofonly spandrel moment resisting frame

22、s to resist wind loads.Deeper, more efficient sections may be used thus minimiz-ing the number of moment resisting connections required.Where appropriate, high strength steel = 50 ksi)should be used in lieu of mild steel = 36 ksi) for bothcolumns and beams. The reason is simplethe price tostrength r

23、atio is about 25% lower for the higher strength steelbeams and 10% to 15% lower for columns depending upontheir length. For example, a W21x44 = 36 ksi) simplefiller beam is the equivalent of a W16x26 = 50 ksi)composite filler beam. The difference in the cost of the millmaterial to the fabricator is

24、about $3.90 per linear foot. Thecost of the studs in place at a cost of $1.50 each is about$1.30 per linear foot. The cost of cambering or shoring isconsiderably less than the $2.60 per foot difference. The floorvibration ratings for the two beams are comparable. Therequired critical damping using M

25、urrays criterion (Murray,1991) for the W21x44 and W16x26 spanning 30 -0 “ spaced10 -0“ o.c. with 10 psf ambient live load is 4.00 and 3.46respectively. The higher strength steel beam is less costlyand functionally equivalent. It should be kept in mind thatthere are situations where the use of high s

26、trength steel isinappropriate. Small inconsequential filler beams, channels,angles, etc., should be of = 36 ksi steel, as this mate-rial is readily available from a fabricators stock or a steelsupply warehouse. Members for which strength is not thecontrolling design consideration, obviously = 36 ksi

27、material should be used.Repetitive use of members and/or the same shape size isan important factor in the design of an economical project.Repetitive use of members reduces the detailing, fabrication,and erection costs. As an example, in composite construc-tion where beam spacing for non-typical area

28、s is reduced,consideration should be given to the use of the typical sizebeam section with a reduction in the number of studs. Thesimpler the framing, the lower the final estimated cost islikely to be at bid time and, as a result, the lower the totalsquare foot cost of the project.Use live load redu

29、ctions for the design of members wherepossible. While live load reduction may not result in any sub-stantial reduction in filler beam weights, a change of one size,perhaps a reduction from a W16x31 to a W16x26, will resultin a 16% savings in the filler beam mill material required.The savings in gird

30、er and column weights and the cost offoundations are likely to be significant.The level of inspection specified should be consistent withthat required to insure that the completed structure will befunctional. Except in unusual circumstances, visual inspec-tion should be adequate for fillet welds. Th

31、e extent of non-destructive testing of butt welds may be finally determinedduring the construction period. If the results of tests are mar-ginal, the number of tests can be increased. If the resultsof the tests are consistently good, the number of tests maybe reduced. Especially for large projects,

32、it may be prudentto require AISC certified fabricators in order to insure goodquality control and a more trouble-free project.Finally, paint only members required by the AISC Speci-fication. Unpainted surfaces should be used when in con-tact with concrete. Fireproofing material more readilyadheres t

33、o unpainted surfaces. While painting costs may onlybe $.15 to $.20 per square foot, for a 200,000 square footproject the cost saving of $30,000 to $40,000 is real and isthere for the taking.LIVE LOAD AND BAY SIZE SELECTIONMost buildings are economic machines of one sort or another.In particular, man

34、y office building structures are built on aspeculative basis. The success of the venture may be a func-tion of the buildings planning and serviceability potential.Larger bay sizes increase the flexibility in space planning.Higher design live loads also increase the flexibility in theuses permitted i

35、n office space. Buildings with higher liveload capacities and larger bay sizes are obviously more attrac-tive to potential building tenants and more valuable to build-ing owners. It will be shown that larger bay sizes and higher1 2003 by American Institute of Steel Construction, Inc. All rights rese

36、rved.This publication or any part thereof must not be reproduced in any form without permission of the publisher.Table 1.Typical Interior Column Load ComparisonDesignASDLRFD50 PSFLL+20 PSFPART100%100%80 PSFLL+ 20 PSFPART110%100 PSFLL100%105%than promulgated minimum live loads can be achieved withno

37、significant increase in cost.Live Load SelectionSometimes developers and/or designers select the minimumlive load permitted by the building code. This is a seeminglyobvious choice if the costs are to be kept to an absolute mini-mum. It is possible to upgrade from the minimum permit-ted design live l

38、oad of 50 psf plus 20 psf partition load toa 100 psf live load capacity (with no additional partition loadallowance) at virtually no increase in cost.As an example, we will compare the differences for a typi-cal office building with 30 ft square bays and 10 stories inheight (Fig. 1). Comparisons wil

39、l be made for 50 psf liveload plus 20 psf partition load, 80 psf live load plus 20 psfpartition load, and 100 psf live with no partition load load-ings. Column load comparisons are shown for a typicalinterior column for the AISC Allowable Stress Design (ASD)Specification (AISC, 1978) and the AISC Lo

40、ad and Resis-tance Factor Design (LRFD) Specification (AISC, 1986).Fig. 1. Typical office building floor plan.Live load reductions are made in accordance with ASCE 7-88(formerly ANSI A58.1). Table 1 is a percentage comparisonof the tabulated column loads at the base of the ten storybuilding for the

41、three design load combinations. For ASDdesign, the column load is identical for that of the 50 psflive load plus 20 psf partition load and the 100 psf live load.Due to the maximum live load reduction of 60%, the 50 psfreduced live load plus the partition load is equal to thereduced 100 psf live load

42、. For the 80 psf live load plus 20psf partition load the column and foundation loads areincreased by 10%. For LRFD the results change due to thedifference in the live load and dead load factors. For thiscase, the column loads are increased by 5% for the 100 psflive loading and 11.5% for the 80 psf p

43、lus 20 psf partitionloading. The increase in costs for the column mill materialfor the 100 psf live loading is $.016 per square foot for theten story building. For either loading case, LRFD will resultin lighter column loads because, essentially, the LRFD deadload factor is smaller (1.2) than a comp

44、arable ASD factor(1.67).Tables 2 and 3 tabulate the comparative costs of a typicalbay floor system for the 30 ft square bay designed for thethree loadings used for the column load comparison for bothASD and LRFD designs. The comparison is made for a dif-ference in mill material costs and the cost of

45、 studs. The costof fabrication and erection remain essentially constant forthe six conditions. It is for that reason that the mill materialplus the stud costs will give a reasonably good comparison.The cost of mill material is taken as $.25 per pound for= 36 ksi and $.28 per pound for = 50 ksi steel

46、s. Theunit prices for both = 36 ksi and = 50 ksi mill mate-rial change periodically. If one desires to make this type ofcost comparison, representative mill material prices may beobtained from local fabricators. As would be expected, the50 psf live load plus 20 psf partition load is the least expen-

47、sive loading condition. However, the premium for the higherlive load capacity (100 psf) condition is only $.09 per squarefoot. Compared to the total cost of the structural system, theadded cost is probably less than 1%.Knowing these facts, many owners may well wish to selectthe higher live load capa

48、city. The real difference in the struc-tures in reality may be semantics, but as a practical matterthe higher load capacity enhances the buildings value and,most of all perhaps, its rentability.Bay Size SelectionThe selection of a smaller bay size to reduce costs may bea fallacy when applied to stee

49、l buildings. For economy, itis important to reduce the number of pieces to be fabricatedand erected. As noted earlier, the cost of fabrication and erec-tion for a small beam is essentially the same as for a largebeam. The savings involved in reducing the member weightis primarily savings in the cost of mill material. When thenumber of pieces is reduced, the actual cost of fabrication2111% 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.and erec