Structural Steel Design LRFD Approach Second Edition J. C. Smith North Carolina SfafeU niversity John Wiley & Sons, Inc. New York Chichester Brisbane Toronfo Singapore ACQUISITIONS EDITOR Cliff Robichaud ASSISTANT EDITOR Catherine Beckham MARKETING MANAGER Debra Reigert PRODUCTION EDITOR Ken Santor COVER DESIGNER Harry Nolan INTERIOR DESIGN Michael Jung MANUFACTURING MANAGER Dorothy Sinclair Recognizing the importance of preserving what has been written, it is a policy of John Wiley & Sons, Inc. to have books of enduring value published in the United States printed on acid-free paper, and we exert our best efforts to that end. The paper on this book was manufactured by a mill whose forest management programs include sustained yield harvesting of its timberlands. Sustained yield harvesting principles ensure that the number of trees cut each year does not exceed the amount of new growth. Copyright 01 996, by John Wiley & Sons, Inc. All rights reserved. Published simultaneously in Canada. Reproduction or translation of any part of this work beyond that permitted by Sections 107 and 108 of the 1976 United States Copyright Act without the permission of the copyright owner is unlawful. Requests for permission or further information should be addressed to the Permissions Department, John Wiley & Sons, Inc. Library of Congress Cataloging-in-Publication Data: Smith, J.C., 1933- Structural steel design : LRFD approach / J.C. Smith.-Znd ed p. cm. Includes bibliographical references and index. ISBN 0-471-10693-3 (cloth: alk. paper) 1. Building, Iron and steel. 2. Steel, Structural. 3. Load factor design. I. Title. TA684S584 1996 624.1’821-dc20 95-36503 CIP 109 8 7654 3 Preface This book has been written to serve as the undergraduate-level textbook for the first two structural steel design courses in Civil Engineering. In this edition, eachchapter was modified to reflect the changes made in the 1993 AISC LRFD Specification for Structural Steel Buildings and the 1994 LRFD Manual of Steel Construction, Second Edition, which consists of Volume I: Structural Members, Specifications, & Codes Volume 11: Connections The chapter on the behavior and design of tension members is located before the chapter on connections for tension members, which is separated from the chapter on other types of connections. Bolted connections for tension members are discussed before welded connections.T he long examples in the first edition have been replaced by shorter ones. Each professor has particular course constraints and preferences of what to present in each course. Chapters 1 to 6 probably contain most of the material that is taughtin the first steeldesigncourse.Chapters7 toll containmaterial tomeet theother needs of each professor. Appendix B gives the review material needed for a thorough understanding of principal axes involved in column and beam behavior. Appendix C provides some formulas for the warping and torsional constants of open sections. The LRFD Specification requires a factored load analysis and permits either an elastic analysis or a plastic analysis. In our capstone structural design course, the students are required to design a steel-framed building and a reinforced-concrete- framed building. Since the ACI Code permits only ,an elastic analysis due to factored loads, I use only the elastic analysis approach in the capstone structural design course. Consequently, Chapter 6 and Appendix A give students a brief but realistic introduc- tion to elastic analysis and design of unbraced frames in the LRFD approach. Chapter 11 should be adequate for those who wish to discuss plastic analysis and design. Appendix D provides some handbook information pertaining to plastic analysis. vi I use the textual material associated with Appendix A in the classroom when- ever appropriate. The reviewers of this edition were: P. R. Chakrabarti, California State University - Fullerton; W. S. Easterling, Virginia Tech; S. C. Goel, University of Michigan; R. B. McPherson, New Mexico State University; and A. C. Singhal, Arizona State University. I am appreciative of their comments, suggestions for improvement, constructive criticisms, and identified errors. J. C. Smith Gontents Chapter 1 Introduction 1 1.1 Structural Steel 1 1.1.1 Composition and Types 1 1.1.2 Manufacturing Process 4 1.1.3 Strength and Ductility 5 1.1.4 Properties and Behavorial Characteristics of Steel 5 1.1.5 Residual Stresses 8 1.1.6 Effect of Residual Stresses on Tension Member Strength 9 1.1.7 Effect of Residual Stresses on Column Strength 11 1.2 Structural Behavior, Analysis, and Design 13 1.3 Idealized Analytical Models 15 1.4 Boundary Conditions 18 1.5 Interior Joints 20 1.6 Loads and Environmental Effects 23 1.6.1 DeadLoads 24 1.6.2 Live Loads 24 Occupancy Loads for Buildings 24 Traffic Loads for Bridges 24 1.6.3 Roof Loads 24 SnowLoads 25 Rain or Ice Loads 25 Roof Live Loads 26 1.6.4 Wind Loads 26 1.6.5 Earthquake Loads 26 1.6.6 Impact Loads 27 1.6.7 Water Pressure and Earth Pressure Loads 27 1.6.8 Induced Loads 27 1.7 Construction Process 27 1.8 Load and Resistance Factor Design 28 1.9 Structural Safety 34 1.10 Sigruficant Digits and Computational Precision 40 Problems 41 vii viii Contents Chapter 2 Tension Members 43 2.1 Introduction 43 2.2 Strength of a Tension Member with Bolted-End Connections 44 2.3 Effect of Staggered Bolt Holes on Net Area 52 2.4 Design of a Tension Member with Bolted-End Connections 59 2.5 Strength of a Tension Member with Welded-End Connections 63 2.6 Design of a Tension Member with Welded-End Connections 67 2.7 Single-Angle Members 69 2.8 ThreadedRods 70 2.9 Stiffness Considerations 71 Problems 73 Chapter 3 Connections for Tension Members 83 3.1 Introduction 83 3.2 Connectors Subjected to Concentric Shear 83 3.3 Bolting 84 3.4 Types of Connections 86 3.4.1 Slip-Critical Connections 86 3.4.2 Bearing-Type Connections 87 3.5 Bolts in a Bearing-Type Connection 87 3.6 Bearing at the Bolt Holes 90 3.7 Connecting Elements in a Bolted Connection 92 3.8 Welding 96 3.9 Fillet Welds 97 3.9.1 Strength of Fillet Welds 97 3.9.2 Design of Fillet Welds 101 3.10 Connecting Elements in a Welded Connection 107 Problems 109 Chapter 4 Columns 118 4.1 Introduction 318 4.2 Elastic Euler Buckling of Columns 119 4.3 Effect of Initial Crookedness on Column Buckling 122 4.4 Inelastic Buckling of Columns 125 4.5 Effective Length 127 4.6 Local Buckling of the Cross-sectional Elements 135 4.7 Flexural-Torsional Buckling of Columns 145 4.8 Built-up Columns 148 4.9 Single-Angle Columns 155 4.10 Story Design Strength 155 Problems 162 Contents ix Chapter5 Beams 168 5.1 Introduction 168 5.2 Deflections 169 5.3 Shear 170 5.4 Bending Behavior of Beams 171 5.5 Plastic Bending 176 5.6 Limiting Width-Thickness Ratios for Compression Elements 184 5.7 Lateral Support 185 5.8 Holes in Beam Flanges 187 5.9 Design Bending Strength 188 5.10 When Local Buckling Governs $Mnx 202 5.11 Built-up Beam Sections 209 5.12 Biaxial Bending of Symmetric Sections 221 5.13 Bending of Unsymmetric Sections 223 5.14 Web and Flanges Subjected to Concentrated Loads 227 5.15 Bearing Stiffeners 236 Problems 241 Chapter 6 Members Subject to Bending and Axial Force 247 6.1 Introduction 247 6.2 Member-Second-Order (P8) Effects 248 6.3 System-Second-Order (PA) Effects 253 6.4 Elastic Factored Load Analyses 255 6.5 Members Subject to Bending and Axial Tension 258 6.6 Beam-Columns 261 6.7 Braced Frame Examples 263 6.8 Unbraced Frame Examples 269 6.9 Preliminary Design 276 Problems 280 Chapter 7 Bracing Requirements 287 7.1 Introduction 287 7.2 Stability of a Braced Frame 287 7.2.1 Required Stiffness and Strength of Cross Braces 289 7.2.2 Required Stiffness and Strength of K Braces 298 7.3 Weak-Axis Stability of a Column 299 7.3.1 Bracing Stiffness and Strength Requirements When h = L/2 301 7.3.2 Bracing Stiffness and Strength Requirements When h = L/3 302 7.3.3 Bracing Stiffness and Strength Requirements When h = L/4 303 7.3.4 Bracing Stiffness and Strength RequirementsW hen h = L/n for Large n 304 7.3.5 When Point of Inflection Does Not Occur at a Braced Point 305 7.3.6 Example Problem 306 7.4 Lateral Stability of a Beam Compression Flange 309 x Contents Chapter 8 Connections 312 8.1 Introduction 312 8.2 Connectors Subjected to Eccentric Shear 312 8.2.1 A Bolt Group Subjected to Eccentric Shear 313 Ulitmate Strength Method 313 Elastic Method 316 8.2.2 A Weld Group Subjected to Eccentric Shear 321 Ulitmate Strength Method 321 Elastic Method 323 8.3 Bolts Subjected to Tension and Prying Action 327 8.4 Bolts Subjected to Tension and Shear 329 8.5 Connectors Subjected to Eccentric Tension and Shear 330 8.5.1 Weld Groups 331 8.5.2 Bolt Groups 333 Elastic Method 334 Ulitmate Strength Method 334 8.6 Truss Member Connections and Splices 336 8.7 Column Base Plates 337 Case 1: (e = MJP,) IH /6 338 Case 2: (e = MJP,) > H/6 339 8.8 ColumnSplices 342 8.9 Simple Shear Connections for Beams 343 8.9.1 Beam Web Connections 343 8.9.2 Unstiffened Beam Seats 344 8.9.3 Stiffened Beam Seats 350 8.9.4 Shear End-Plate Connections 353 8.9.5 Bracket Plates 353 8.10 Moment Connections for Beams 353 8.10.1 Beam-to-Beam Connections and Splices 353 8.10.2 Beam-to-Column Connections 354 8.11 Knee or Corner Connections 356 Problems 360 Chapter 9 Plate Girders 366 9.1 Introduction 366 9.2 Conventional Design Method 370 9.2.1 Design Strength Definitions 371 9.2.2 Intermediate Stiffener Requirements 375 9.2.3 Design Examples 375 9.3 Tension Field Design Method 387 9.3.1 Design Strength Definitions 388 9.3.2 Intermediate Stiffener Requirements 389 9.3.3 Design Examples 391 Problems 397 Contents xi Chapter 10 Composite Members 399 10.1 Introduction 399 10.2 Composite Columns 399 10.2.1 Limitations 402 10.2.2 Column Design Strength 403 10.3 Composite Beams with Shear Connectors 408 10.3.1 Composite Construction 408 10.3.2 Effective Concrete Flange Width 409 10.3.3 Shear Design Strength 410 10.3.4 Shear Connectors 410 10.3.5 Flexural Design Strength 418 Positive Moment Region 418 Negative Moment Region 419 10.4 Concrete-Encased Beams 429 10.5 Deflections of Composite Beams 431 10.6 Composite Beam-Columns 435 10.7 Design Examples 438 Problems 438 Chapter 11 Plastic Analysis and Design 440 11.1 Introduction 440 11.2 Plastic Hinge 440 11.3 Plastic Collapse Mechanism 445 11.4 Equilibrium Method of Analysis 448 11.5 Virtual Work Method of Analysis 471 11.6 Jointsize 490 Problems 493 Appendix A Computer Output for an Elastic,Factored Load Analy- sis of a Plane Frame 499 Appendix B Cross-Sectional Properties and Flexure 508 B.1 Notation 508 B.2 Centroidalhes 509 B.3 Moments and Product of Inertia 509 B.4 Transfer Axes Formulas 509 8.5 Summation Formulas 510 B.6 Principal Axes 513 B.7 Using Mohr’s Circle to Find the Principal Axes 513 B.8 Radius of Gyration 515 B.9 Properties of a Steel L Section 516 B.10 Flexure Formula 518 B.11 Biaxial Bending 519 Problems 521 xii Contents Appendix C Torsional Properties 524 Appendix D Plastic Analysis Formulas 526 References 531 Index 533