1、29Steel Design GuideVertical Bracing ConnectionsAnalysis and DesignDG29_cover.indd 1 1/8/2015 8:39:30 AMAMERICAN INSTITUTE OF STEEL CONSTRUCTIONVertical Bracing Connections Analysis and DesignLarry S. Muir, P.E.AISC Atlanta, GAWilliam A. Thornton, Ph.D., P.E.Cives Steel CorporationRoswell, Georgia29
2、Steel Design GuideAISC 2014byAmerican Institute of Steel ConstructionAll rights reserved. This book or any part thereof must not be reproduced in any form without the written permission of the publisher.The AISC logo is a registered trademark of AISC.The information presented in this publication has
3、 been prepared in accordance with recognized engineering principles and is for general information only. While it is believed to be accurate, this information should not be used or relied upon for any specific application without competent professional examination and verification of its accuracy, s
4、uitability and applicability by a licensed professional engineer, designer or architect. The publication of the material contained herein is not intended as a representation or warranty on the part of the American Institute of Steel Construction or of any other person named herein, that this informa
5、tion is suitable for any general or particular use or of freedom from infringement of any patent or patents. Anyone making use of this information assumes all liability arising from such use.Caution must be exercised when relying upon other specifications and codes developed by other bodies and inco
6、rporated by reference herein since such material may be modified or amended from time to time subsequent to the printing of this edition. The Institute bears no responsibility for such material other than to refer to it and incorporate it by reference at the time of the initial publication of this e
7、dition.Printed in the United States of AmericaiAuthorsLarry S. Muir, P.E. is the Director of Technical Assistance in the AISC Steel Solutions Center. He is a member of both the AISC Committee on Specifications and the Committee on Manuals.William A. Thornton, Ph.D., P.E. is a corporate consultant to
8、 Cives Corporation in Roswell, GA. He was Chairman of the AISC Committee on Manuals for over 25 years and still serves on the Committee. He is also a member of the AISC Committee on Specifications and its task committee on Connections.AcknowledgmentsThe authors wish to acknowledge the support provid
9、ed by Cives Steel Company during the devel-opment of this Design Guide and to thank the American Institute of Steel Construction for fund-ing the preparation of this Guide. The ASCE Committee on Design of Steel Building Structures assisted in the development of Appendix D. They would also like to th
10、ank the following people for assistance in the review of this Design Guide. Their comments and suggestions have been invaluable.Leigh Arber Scott Armbrust Bill Baker Charlie Carter Carol Drucker Cindi Duncan Lanny Flynn Scott Goodrich Pat Hassett Steve Herlache Steve Hofmeister Larry Kloiber Bill Li
11、ndley Margaret Matthew Ron Meng Chuck Page Bill Pulyer Ralph Richard Dave Ricker Tom Schlafly Bill Scott Bill Segui Victor Shneur Gary Violette Ron YeagerPrefaceThis Design Guide provides guidance for the design of braced frame bracing connections based on structural principles and adhering to the 2
12、010 AISC Specification for Structural Steel Buildings and the 14th Edition AISC Steel Construction Manual. The content expands on the discussion provided in Part 13 of the Steel Construction Manual. The design examples are intended to pro-vide a complete design of the selected bracing connection typ
13、es, including all limit state checks. Both load and resistance factor design and allowable stress design methods are employed in the design examples.iiiiiTABLE OF CONTENTSCHAPTER 1 INTRODUCTION . 11.1 OBJECTIVE AND SCOPE11.2 DESIGN PHILOSOPHY .1CHAPTER 2 COMMON BRACING SYSTEMS 32.1 ANALYSIS CONSIDER
14、ATIONS .32.2 CHEVRON BRACED FRAMES (CENTER TYPE) 3CHAPTER 3 BRACE-TO-GUSSET CONNECTION ARRANGEMENTS . 93.1 SMALL WIDE-FLANGE BRACES93.2 LARGE WIDE-FLANGE BRACES 93.3 ANGLE AND WT-BRACES113.4 CHANNEL BRACES 113.5 FLAT BAR BRACES 113.6 HSS BRACES .11CHAPTER 4 DISTRIBUTION OF FORCES . 174.1 OVERVIEW OF
15、 COMMON METHODS .174.1.1 Corner Connections.174.1.2 Central or Chevron Connections 214.1.3 Comparison of DesignsUniform Force Method vs. Parallel Force Method .224.2 THE UNIFORM FORCE METHOD . 244.2.1 The Uniform Force Method General Case .244.2.2 Nonconcentric Brace Force Special Case 1 294.2.3 Red
16、uced Vertical Brace Shear Force in Beam-to-Column Connection Special Case 2 314.2.4 No Gusset-to-Column Connection Special Case 3 324.2.5 Nonorthogonal Corner Connections 334.2.6 Effect of Frame Distortion . 344.3 BRACING CONNECTIONS TO COLUMN BASE PLATES 37CHAPTER 5 DESIGN EXAMPLES. 435.1 CORNER CO
17、NNECTION-TO-COLUMN FLANGE: GENERAL UNIFORM FORCE METHOD 435.2 CORNER CONNECTION-TO-COLUMN FLANGE: UNIFORM FORCE METHOD SPECIAL CASE 1 785.3 CORNER CONNECTION-TO-COLUMN FLANGE: UNIFORM FORCE METHOD SPECIAL CASE 2 845.4 CORNER CONNECTION-TO-COLUMN FLANGE WITH GUSSET CONNECTED TO BEAM ONLY: UNIFORM FOR
18、CE METHOD SPECIAL CASE 3 985.5 CORNER CONNECTION-TO-COLUMN WEB: GENERAL UNIFORM FORCE METHOD .1185.6 CORNER CONNECTION-TO-COLUMN WEB: UNIFORM FORCE METHOD SPECIAL CASE 1 .1475.7 CORNER CONNECTION-TO-COLUMN WEB: UNIFORM FORCE METHOD SPECIAL CASE 2 .1635.8 CORNER CONNECTION-TO-COLUMN WEB WITH GUSSET C
19、ONNECTED TO BEAM ONLY: UNIFORM FORCE METHOD SPECIAL CASE 3 .1785.9 CHEVRON BRACE CONNECTION .1895.10 NONORTHOGONAL BRACING CONNECTION .2055.11 TRUSS CONNECTION2375.12 BRACE-TO-COLUMN BASE PLATE CONNECTION .2685.12.1 Strong-Axis Case .2685.12.2 Weak-Axis Case 284CHAPTER 6 DESIGN OF BRACING CONNECTION
20、S FOR SEISMIC RESISTANCE. 2916.1 COMPARISON BETWEEN HIGH-SEISMIC DUCTILE DESIGN AND ORDINARY LOW-SEISMIC DESIGN .291Example 6.1a High-Seismic Design in Accordance with the AISC Specification and the AISC Seismic Provisions 292Example 6.1b Bracing Connections for Systems not Specifically Detailed for
21、 Seismic Resistance (R=3) . 321 APPENDIX A. DERIVATION AND GENERALIZATION OF THE UNIFORM FORCE METHOD . 347A.1 GENERAL METHOD.347A.1.1 Beam Control Point347A.1.2 Gusset Control Point .348A.1.3 Determination of Forces .349A.1.4 Accounting for the Beam Reaction 350ivExample A.1 Vertical Brace-to-Colum
22、n Web Connection Using an Extended Single Plate 351APPENDIX B. USE OF THE DIRECTIONAL STRENGTH INCREASE FOR FILLET WELDS . 371APPENDIX C. BUCKLING OF GUSSET PLATES 374C.1 BUCKLING AS A STRENGTH LIMIT STATETHE LINE OF ACTION METHOD 374C.2 BUCKLING AS A HIGH-CYCLE FATIGUE LIMIT STATEGUSSET PLATE EDGE
23、BUCKLING .374C.3 BUCKLING AS A LOW-CYCLE FATIGUE LIMIT STATEGUSSET PLATE FREE EDGE BUCKLING .377C.4 AN APPROACH TO GUSSET PLATE FREE EDGE BUCKLING USING STATICALLY ADMISSIBLE FORCES (THE ADMISSIBLE FORCE MAINTENANCE METHOD) 380C.5 APPLICATION OF THE FREE EDGE APPROACH TO EXAMPLE 6.1a .382APPENDIX D.
24、 TRANSFER FORCES 383D.1 THE EFFECT OF CONNECTION CONFIGURATION ON THE TRANSFER FORCE383D.2 PRESENTATION OF TRANSFER FORCES IN DESIGN DOCUMENTS .384D.3 ADDITIONAL CONSIDERATIONS .386D.4 EFFECTS OF MODELING ASSUMPTIONS ON TRANSFER FORCES 387REFERENCES. 390AISC DESIGN GUIDE 29 / VERTICAL BRACING CONNEC
25、TIONSANALYSIS AND DESIGN / 1Chapter 1 Introduction1.1 OBJECTIVE AND SCOPEThis Design Guide illustrates a method for the design of braced frame bracing connections based on structural prin-ciples, and presents the design basis and complete design examples illustrating the design of:1. All orthogonal
26、and nonorthogonal connections involving a brace, a beam and a column (corner type)2. Connections involving a beam or column and one or two braces, such as chevron or K-bracing, and eccentric braces (center type)3. Connections of braces to columns at column base plates (base type)4. Both nonseismic a
27、nd seismic situations are covered1.2 DESIGN PHILOSOPHYAll structural design, except for that which is based directly on physical testing, is based either explicitly or implicitly on the principle known as the lower bound theorem of limit anal-ysis. This theorem is important because it allows structu
28、ral engineers to be confident that 1) their assumptions about the internal force field will not over-predict the strength of an indeterminate structure, and 2) different methodologies for determining an admissible force field, while they may vary significantly in their predictions of the available s
29、trength, are nonetheless all valid. This theorem, which was first proven in the form given in the following in the 1950s (Baker et al., 1956), states that:Given: An admissible internal force field (i.e., a distri-bution of internal forces in equilibrium with the applied load)Given: Satisfaction of a
30、ll applicable limit statesThen: The external load in equilibrium with the internal force field is less than, or at most equal to, the connection capacity.The lower bound theorem is applicable to ductile limit states, and most connection limit states have some ductility. For instance, bolts in shear
31、undergo significant shear deforma-tion, on the order of a in. for a w-in.-diameter bolt, before fracture. Limit states such as block shear and net shear can accommodate significant distortion of the material before fracture. Plate or column buckling, while generally con-ceived as a nonductile limit
32、state, is in a sense a ductile limit state; when a plate or column buckles, it does not become incapable of supporting any load, but rather will continue to support the buckling load as long as any excess load can be distributed to other components of the structural system. This phenomenon can be ob
33、served in the laboratory when a displacement-type testing machine is used. If a force-type machine is used, the load will increase continuously, and kinking and complete collapse will occur.Actually all structural design relies on the validity of the lower bound theorem. For instance, if a building
34、is modeled by a frame analysis computer program, a certain distribution of column loads will result. This distribution is dependent on thousands of assumptions. Shear connections are assumed not to carry any moment at all, and moment connections are assumed to maintain the angle between members. Nei
35、ther assumption is true. Therefore, the column design loads at the footings will sometimes be drastically different from the actual loads, if these loads were measured. Some columns will be designed for loads smaller than the true load, and some will be designed for larger loads. Because of the lowe
36、r bound theorem, this is not a concern.Ductility can also be provided to an otherwise nonduc-tile system by support flexibility. For instance, transversely loaded fillet welds are known to have limited ductility. If a plate is fillet welded near the center of a column or beam web and subjected to a
37、load transverse to the web, the flexibility of the web under transverse load will tend to mitigate the low ductility of the fillet weld and will allow redistribution to occur. This same effect can be achieved with transversely loaded fillet welds to rigid supports by using a fillet weld larger than
38、that required for the given loads. The larger fillet weld allows the given applied loads to redistribute within the length of the weld without local fracture.The term “admissible force field” perhaps needs some fur-ther explanation. Bracing connections are inherently stati-cally indeterminate. There
39、fore, there will be many possible force distributions within the connection. All of those force distributions that satisfy equilibrium are said to be “admis-sible” or “statically admissible.” There are theoretically an infinite number of possible admissible force fields for any statically indetermin
40、ate structure. There will also be an infi-nite number of internal force fields that do not satisfy equi-librium; these are said to be “inadmissible.” If such a force field is used, the lower bound theorem is not valid and any design obtained with this inadmissible force field cannot be said to be sa
41、fe; i.e., the failure load may be less than the applied load. When an admissible force field is used, the calculated failure load will be less than, or at most equal to, the load at which failure occurs; therefore, a safe design is achieved.2 / VERTICAL BRACING CONNECTIONSANALYSIS AND DESIGN / AISC
42、DESIGN GUIDE 29AISC DESIGN GUIDE 29 / VERTICAL BRACING CONNECTIONSANALYSIS AND DESIGN / 3Chapter 2 Common Bracing SystemsFigure 2-1 shows some common concentric bracing con-figurations. The sketches of the member are meant to show the member orientation (all elements are W-shapes), which is often mi
43、ssing on computer generated drawings. These sketches are not meant to show work point locations. In a concentrically braced frame, the gravity axes of all mem-bers at any one joint (such as Detail A of Figure 2-1) meet at a common point, called the work point (W.P.). Figure 2-2 shows the connection
44、at Detail A of Figure 2-1(a). As with trusses, all joints in concentrically braced frames are assumed to be pinned.Nonconcentrically braced frames are similar to concentri-cally braced frames; however, the work point is not located at the common gravity axis point. Figure 2-3 illustrates a nonconcen
45、tric bracing arrangement. The work point location results in a couple at the joint. This couple must be con-sidered in the design of the systems connections and main members in order to ensure that the internal force system is admissible. In many cases, this couple will be small and will not affect
46、member size.Eccentrically braced frames have a different appearance than concentrically braced frames. The braces intersect the beams at points quite distinct from the usual joint working point, as shown in Figure 2-4. Eccentrically braced frames can be used to provide better access through the brac
47、ed bay for doors, windows or equipment access. They are also used in seismic design because they can provide significant inelastic deformation capacity primarily through shear or flexural yielding in the links.2.1 ANALYSIS CONSIDERATIONSBraced frames can be analyzed as simple trusses with all joints
48、 pinned. In most cases, secondary forces (also called distortional or rotational forces) due to joint rigidity can be ignored. The AASHTO Bridge Code (AASHTO, 2012) Section 6.14.2.3, for example, states that these forces can be ignored if member lengths are greater than 10 times their cross-sectiona
49、l dimension in the plane of distortion. In regions of high seismicity, braced frames can be designed as pinned, but corner connections (those involving a column, beam and brace) may have to explicitly include consider-ation of distortional forces in the design of the connections. In concentrically braced frames, all members are assumed to be subjected only to axial forces due to lateral loads. This greatly simplifies the structural analysis because, in many cases, the frame will be statically determinate.In nonconcentrically braced frames, it is common prac-tice to analyze th
