Structural Steel Design - LRFD Approach

503 Pages·1996·21.484 MB·English

by  Smith, J. C.

Structural Steel Design
LRFD Approach
Second Edition
J. C. Smith
North Carolina SfafeU niversity
John Wiley & Sons, Inc.
New York Chichester Brisbane Toronfo Singapore
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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before welded connections.T he long examples in the first edition have been replaced
by shorter ones.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