Steel Structures Design About the Author Alan Williams, Ph.D., S.E., F.I.C.E., C. Eng., is a registered structural engineer in California who has had extensive experience in the practice and teaching of structural engi- neering. In California, he has worked as a Senior Trans- portation Engineer in the Department of Transportation and as Principal for Structural Safety in the Division of the State Architect. His prior positions include Professor of Structural Analysis at Ahmadu Bello University, Nigeria, and consulting structural engineer in South Africa and the United States. Dr. Williams’ practical experience includes the design and construction of bridges, schools, and commercial and industrial structures. The author obtained his bachelor of science degree and doctorate from Leeds University and has published 13 papers and nine books on structural engineering top- ics. Dr. Williams is a member of the Structural Engineers Association of Southern California, Fellow and Life Member of the Institution of Civil Engineers, and a Chartered Engineer in the United Kingdom. About the International Code Council The International Code Council (ICC), a membership association dedicated to building safety, fire prevention, and energy efficiency, develops the codes and standards used to construct residential and commercial buildings, including homes and schools. The mission of ICC is to provide the highest quality codes, standards, products, and services for all concerned with the safety and per- formance of the built environment. Most U.S. cities, coun- ties, and states choose the International Codes, building safety codes developed by the ICC. The International Codes also serve as the basis for construction of federal properties around the world, and as a reference for many nations outside the United States. The ICC is also dedi- cated to innovation and sustainability and Code Council subsidiary, ICC Evaluation Service, issues Evaluation Reports for innovative products and reports of Sustaina- ble Attributes Verification and Evaluation (SAVE). Headquarters: 500 New Jersey Avenue, NW, 6th Floor, Washington, DC 20001-2070 District Offices: Birmingham, AL; Chicago, IL; Los Angeles, CA 1-888-422-7233 www.iccsafe.org Steel Structures Design Alan Williams New York Chicago San Francisco Lisbon London Madrid Mexico City Milan New Delhi San Juan Seoul Singapore Sydney Toronto Copyright © 2011 by The McGraw-Hill Companies, Inc. All rights reserved. Except as permitted under the United States Copyright Act of 1976, no part of this publication may be reproduced or distributed in any form or by any means, or stored in a database or retrieval system, without the prior written permission of the publisher. 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Contents Preface ..................................................... xv Nomenclature ............................................... xvii 1 Steel Buildings and Design Criteria ........................... 1 1.1 Introduction ........................................... 1 1.2 Types of Steel Buildings ................................. 5 1.3 Building Codes and Design Criteria ....................... 8 1.4 ASD and LRFD Concepts ................................ 9 References .................................................. 1 2 Problems ................................................... 1 2 2 Design Loads ............................................... 15 2.1 Introduction ........................................... 1 5 2.2 Dead Loads ............................................ 1 6 Tributary Area ....................................... 1 6 Slab Supports ........................................ 1 6 Dead Load Applied to Beams .......................... 1 7 Dead Load Applied to Girders ......................... 1 9 Dead Load Applied to Columns ........................ 2 1 Two-Way Slabs ...................................... 2 4 2.3 Live Loads ............................................ 2 5 Continuous Beam Systems ............................ 2 5 Influence Area ....................................... 2 6 Reduction in Floor Live Load .......................... 2 7 Reduction in Roof Live Load .......................... 3 1 Combined Dead and Live Load ........................ 3 3 2.4 Snow Loads ........................................... 3 4 Flat Roof ............................................ 3 4 Ground Snow Load .................................. 3 4 Flat Roof Snow Load ................................. 3 4 Exposure Factor ...................................... 3 5 Thermal Factor ...................................... 3 5 Importance Factor .................................... 3 5 Rain-on-Snow Surcharge Load ......................... 3 6 Snow Drifts on Lower Roofs ........................... 3 8 Leeward Snow Drifts ................................. 3 8 Windward Snow Drifts ............................... 4 2 Sloped Roof Snow Load ............................... 4 4 Slope Factor ......................................... 4 5 Warm Roof Slope Factor .............................. 4 5 Cold Roof Slope Factor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 5 v vi Contents Contents vii Unbalanced Snow Load for Hip and Gable Roofs ........ 4 6 Unbalanced Snow Load for Gable Roof with W Ä 20 ft ........................................ 4 7 Unbalanced Snow Load for Gable Roof with W > 20 ft ....................................... 4 8 Sliding Snow ........................................ 5 1 Snow Load on Continuous Beam Systems ............... 5 4 2.5 Soil Lateral Load ....................................... 5 5 Earth Pressure at Rest ................................. 5 5 2.6 Flood Loads ........................................... 5 5 Loads during Flooding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 5 Hydrostatic Loads .................................... 5 5 Hydrodynamic Loads ................................ 5 5 Wave Loads ......................................... 5 6 Impact Loads ........................................ 5 6 2.7 Rain Loads ............................................ 5 6 Design Rain Loads ................................... 5 6 Ponding Instability ................................... 5 7 2.8 Wind Loads ........................................... 5 7 Exposure Category ................................... 5 9 Basic Wind Speed .................................... 5 9 Low-Rise Building ................................... 6 1 Regular Building ..................................... 6 1 Simple Diaphragm Building ........................... 6 1 Velocity Pressure Exposure Coefficient .................. 6 1 Site Topography ..................................... 6 1 Directionality Factor .................................. 6 2 Velocity Pressure ..................................... 6 2 ASCE 7 Chapter 28 Part 1—Envelope Procedure ......... 6 3 Rigidity of the Structure ............................... 6 4 Gust Effect Factor .................................... 6 4 Enclosure Classifications .............................. 6 4 Design Wind Pressure on MWFRS for Low-Rise, Rigid Buildings .................................... 6 5 Design Wind Pressure on Components and Cladding . . . . . 6 7 Design of Components and Cladding Using ASCE 7 Sec. 30.4 ........................................... 6 8 IBC Alternate All-Heights Method ...................... 7 1 Velocity Pressure Exposure Coefficient .................. 7 2 Topography Factor ................................... 7 2 Wind Stagnation Pressure ............................. 7 2 Wind Importance Factor .............................. 7 3 Net-Pressure Coefficient .............................. 7 3 Design Wind Pressure on MWFRS: IBC Alternate All-Heights Method ................................ 7 3 Design Wind Pressure on Components and Cladding: IBC Alternate All-Heights Method .................... 7 6 vi Contents Contents vii 2.9 Seismic Loads .......................................... 7 8 Ground Motion Parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 0 Site Classification Characteristics ....................... 8 0 Site Coefficients ...................................... 8 0 Adjusted Earthquake Response Accelerations ............ 8 1 Design Response Acceleration Parameters ............... 8 1 Occupancy Category and Importance Factors ............ 8 3 Seismic Design Category .............................. 8 3 Seismic Force-Resisting System ........................ 8 5 Response Modification Coefficient ...................... 8 6 Fundamental Period of Vibration ....................... 8 9 Seismic Response Coefficient .......................... 8 9 Effective Seismic Weight .............................. 9 2 Seismic Base Shear ................................... 9 3 Vertical Distribution of Seismic Forces .................. 9 3 Diaphragm Loads .................................... 9 5 Flexible Diaphragms ................................. 9 6 Anchorage of Structural Walls to Diaphragms ............ 9 9 Rigid Diaphragms .................................... 104 Lateral Design Force on Structural Walls ................ 109 Lateral Design Force on Parapets ....................... 109 Redundancy Factor ................................... 110 2.10 Load Combinations ..................................... 114 Strength Design Load Combinations .................... 115 Allowable Stress Load Combinations ................... 117 Strength Design Special Load Combinations ............. 119 Allowable Stress Design Special Load Combinations ...... 120 2.11 Serviceability Criteria ................................... 120 Deflection ........................................... 121 Drift ................................................ 121 Vibration ............................................ 122 Durability ........................................... 122 References .................................................. 122 Problems ................................................... 123 3 Behavior of Steel Structures under Design Loads ............... 129 3.1 Introduction ........................................... 129 3.2 Gravity Load-Resisting Systems .......................... 129 Simple Connections .................................. 129 Fully Restrained (FR) Moment Connections ............. 135 Partially Restrained (PR) Moment Connections .......... 140 3.3 Lateral Load-Resisting Systems .......................... 144 Diaphragms ......................................... 144 Collectors ........................................... 145 Steel Deck Diaphragms ............................... 151 Frames Subjected to Lateral Forces ..................... 156 viii Contents Contents ix 3.4 Approximate Methods for Laterally Loaded Frames ......... 160 Portal Method ....................................... 160 Cantilever Method ................................... 163 References .................................................. 167 Problems ................................................... 168 4 Design of Steel Beams in Flexure .............................. 171 4.1 Introduction ........................................... 171 Flexural Limit States .................................. 171 Lateral Bracing of Beams .............................. 172 Design Flexural Strength and Allowable Flexural Strength ... 173 4.2 Plastic Moment of Resistance ............................ 175 Shape Factor and ASD ................................ 176 Built-Up Sections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 177 4.3 Compact, Noncompact, and Slender Sections .............. 179 Compact Section . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 179 Noncompact Section ................................. 181 Slender Section ...................................... 182 4.4 Lateral-Torsional Buckling Modification Factor ............. 182 4.5 Lateral-Torsional Buckling ............................... 185 Plastic Mode: L < L ................................. 185 b p Plastic Mode Extended: L < L ≤ L ..................... 187 p b m Inelastic Mode: L < L ≤ L . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 188 p b r Elastic Mode: L > L ................................... 190 b r 4.6 Weak Axis Bending ..................................... 191 Compact Flanges ..................................... 191 Noncompact Flanges ................................. 192 4.7 Biaxial Bending ........................................ 194 Overhead Traveling Bridge Crane ...................... 195 4.8 Singly Symmetric Sections in Bending ..................... 198 Plastic Mode ........................................ 199 Lateral-Torsional Buckling ............................ 199 Flange Local Buckling ................................ 199 Stem Local Buckling .................................. 200 4.9 Redistribution of Bending Moments in Continuous Beams ... 201 4.10 Deflection Limits ....................................... 204 References .................................................. 204 Problems ................................................... 204 5 Design of Steel Beams for Shear and Torsion ................... 209 5.1 Introduction ........................................... 209 5.2 Shear in Beam Webs .................................... 211 Web Yielding ........................................ 212 Inelastic Buckling .................................... 214 Elastic Buckling ...................................... 216 5.3 Weak Axis Shear ....................................... 218 5.4 Longitudinal Shear in Built-Up Sections ................... 219 viii Contents Contents ix 5.5 Block Shear ........................................... 221 Block Shear Strength for Bolted Connections ............. 222 Effective Bolt Hole Diameter and Net Area .............. 223 Block Shear Strength for Welded Connections ............ 225 Block Shear Strength for Coped Beams .................. 226 5.6 Web Local Yielding ..................................... 228 Bearing on Concrete .................................. 229 Web Yielding at Support .............................. 231 Web Yielding at Girder Interior ........................ 233 5.7 Web Crippling ......................................... 234 5.8 Web Sidesway Buckling ................................. 235 5.9 Design for Torsion ...................................... 237 Torsion in Closed Sections ............................. 237 Torsion in Open Sections .............................. 238 Specification Provisions ............................... 239 Round HSS Subject to Torsion ......................... 240 Rectangular HSS Subject to Torsion ..................... 241 W-Shape Subject to Torsion ............................ 244 References .................................................. 249 Problems ................................................... 250 6 Design of Compression Members ............................. 255 6.1 Introduction ........................................... 255 Compression Limit State .............................. 255 6.2 Effective Length ........................................ 257 Tabulated Factors .................................... 257 6.3 Alignment Charts ...................................... 259 Alignment Chart for Braced Frame ..................... 260 Alignment Chart for Sway Frame ...................... 261 Stiffness Reduction Factors ............................ 263 6.4 Axially Loaded Compression Members .................... 264 Flexural Buckling of Members without Slender Elements .......................................... 264 Torsional and Flexural-Torsional Buckling of Members without Slender Elements ........................... 268 Single Angle Compression Members without Slender Elements .......................................... 271 Members with Slender Elements ....................... 273 6.5 Built-Up Sections ....................................... 279 6.6 Column Base Plates ..................................... 282 Concrete Footing Capacity ............................ 282 Base Plate Thickness .................................. 285 6.7 Column Flanges with Concentrated Forces ................. 287 Introduction ......................................... 287 Flange Local Bending ................................. 287 Web Compression Buckling ........................... 290 Web Panel Zone Shear ................................ 292