DESIGN OF STEEL STRUCTURES

DESIGN OF STEEL STRUCTURES Elias G. Abu·Saba Associate Professor of Architectural Engineering North Carolina Agricultural and Technical State University

SPRINGER-SCIENCE+BUSINESS MEDIA, B.v

DESIGN OF STEEL STRUCTURES Elias G. Abu·Saba Associate Professor of Architectural Engineering North Carolina Agricultural and Technical State University

SPRINGER-SCIENCE+BUSINESS MEDIA, B.v

Copyright © 1995 Springer Science+Business Media Dordrecht Original1y pub1ished by Chapman & Hall in 1995 Softcover reprint ofthe hardcover 1st edition 1995

All rights reserved. No part of this work covered by the copyright hereon may be reproduced or used in any form or by any means-graphic, electronic, or mechanical, including photocopying, recording, taping, or information storage and retrieval systems-without the written permission of the publisher.

1 234567 8 9 10 XXX 01 009997 9695

Library of Congress Cataloging-in-Publication Data

Abu-Saba, Elias G., Design of steel structures / by Elias G. Abu-Saba.

p. cm. Includes bibliographical references and index. ISBN 978-1-4613-5864-0 ISBN 978-1-4615-2079-5 (eBook) DOI 10.1007/978-1-4615-2079-5 1. Building, Iron and steel. 2. Structural design. 3. Load factor design. 1. Title.

TA684.A144 1995 693' .71-dc20 94-48546

CIP

I dedicate this book to the memory of my parents, Jurjis and Sabat Abu-Saba, who did not have the privilege to go to school. Yet they believed in the power of knowledge and provided us, their children, with the opportunity to learn and grow.

The infinite spans the human mind. The spirit spins free of space and time. The joy and sadness of life are a wink In the eternal flow. The stream cascades and meanders To merge and be lost in the greater sea.

ELIAS G. ABU-SABA

November 6. 1994

Contents

Preface xiii

1 Introduction 1

1.1 Introduction 1 1.2 Structural Steel and Its Properties in Construction 4 1.3 Applications 7 1.4 Loads, Load Factors, and Load Combinations 13

2 Tension Members 14

2.1 Introduction 14 2.2 Design Criteria 14 2.3 ASD Method 15 2.4 LRFD Method 17 2.5 Effective Area of Riveted and Bolted Tension Members 20 2.6 Effective Area for Staggered Holes of Tension Members 21 2.7 Tension Rods in Design of Purlins 27 2.8 Limitation of Length of Tension Members on Stiffness:

Slenderness Ratio 25 2.9 Applications 25

3 Compression Members

3.1 Introduction 3.2 Derivation of Euler's Formula 3.3 Design Criteria for Compression Members Under

oncentric Load: ASD Method 3.4 Effective Length and Slenderness Ratio 3.5 Design Criteria for Compression Members

Under Concentric Load: LRFD Method

46

46 47

49 51

54

ix

x Contents

3.6 SI LRFD Design Criteria (Axial Compression) 60 3.7 Compression Members in Braced Frames: ASD Method 63 3.8 Axial Compression and Bending: ASD Method 64 3.9 Reduction in Live Loads 65 3.10 Columns Subject to Bending and Axial Force in a

Braced System: LRFD Method 3.11 Design of Columns for Braced and Unbraced Frames:

ASDMethod 82

4 Designs of Bending Members 106

4.1 Introduction 106 4.2 Simple Bending 106 4.3 Design of Beams and Other Flexural Members:

ASD Allowable Bending Stress 109 4.4 Deflections and Vibrations of Beams in Bending 116 4.5 Design for Flexure: LRFD Method 124 4.6 Use of the Load Factor Design Selection Table Zx

for Shapes Used as Beams 1128 4.7 Serviceability Design Considerations and the

LRFDMethod 132

5 Torsion and Bending 133

5.1 Introduction 133 5.2 Torsional Stresses 133 5.3 Plane Bending Stresses 137 5.4 Combining Torsional and Bending Stresses 137 5.5 Torsional End Conditions 138 5.6 Torsional Loading and End Conditions 139 5.7 Applications 144

6 Design of Bracings for Wind and Earthquake Forces 150

6.1 Introduction 150 6.2 Wind Forces 150 6.3 Wind Velocity Pressure 151 6.4 Selection of Basic Wind Speed (mph) 155

6.5 External Pressures and Combined External and Internal Pressures

6.6 Wind Pressure Profile Against Buildings 6.7 Analysis of Braced Frames for Wind Forces 6.8 Introduction to Seismic Design 6.9 Equivalent Static Force Procedure

Contents xi

155 165 166 175 177

7 Connections 187

7.1 Introduction 187 7.2 Types of Connections 187 7.3 Framed Beam Connection: Bolted 190 7.4 Framed Beam Connection: Welded E70XX Electrodes for

Combination with Table II and Table III Connections 196

8 Anchor Bolts and Baseplates 201

8.1 Introduction 201 8.2 Design of Column Baseplates 201

9 Built-Up Beams: Plate Girders 210

9.1 Introduction 9.2 Design of Plate Girders by ASD Method 9.3 Approximate Method for Selection of Trial Section

10 Composite Construction

10.1 Introduction 10.2 Design Conceptualization and Assumptions 10.3 Development of Section Properties 10.4 Short-Cut Method for Determining Sxbc

10.5 Shear Connectors 10.6 Bethlehem Steel Table for Selecting Shear Connectors 10.7 LRFD Method: Design Assumptions 10.8 LRFD Flexural Members

210 210 214

246

246 246 249 264 282 284 285 287

xii Contents

11 Plastic Analysis and Design of Structures 294

11.1 Introduction 294 11.2 Bending of Beams 294 11.3 Design of Beams: Failure Mechanism Approach 301 11.4 Fixed End Beam 308 11.5 Plastic Hinges: Mechanism of Failure 310 11.6 Fixed End Beam with Multiple Concentrated Loads 317 11.7 Continuous Beams 319 11.8 Portal Frames 329 11.9 Minimum Thickness (Width-Thickness Ratio) 332 11.10 Plastic Analysis of Gabled Frames 337

12 Influence of Axial Forces on Plastic Moment 340

12.1 Introduction 340 12.2 Influence of Axial Forces on Plastic Moment Capacity 340

13 Rigid Connections 350

13.1 Introduction 351 13.2 Straight Corner Connection 355 13.3 Stiffener for a Straight Corner Connection 357 13.4 Haunched Connections 364 13.5 Haunched Connections with Concentrated Loads 368 13.6 Design Guides: Connections

14 Multistory Buildings: Plastic Design

14.1 Introduction 14.2 Allowable Stress vs. Plastic Design Methods 14.3 Application to Multistory Buildings

Index

375

375

376 376 379

389

Preface

This book is intended for classroom teaching in architectural and civil engineering at the graduate and undergraduate levels. Although it has been developed from lecture notes given in structural steel design, it can be useful to practicing engineers. Many of the examples presented in this book are drawn from the field of design of structures.

Design of Steel Structures can be used for one or two semesters of three hours each on the undergraduate level. For a two-semester curriculum, Chapters 1 through 8 can be used during the first semester. Heavy emphasis should be placed on Chapters 1 through 5, giving the student a brief exposure to the consideration of wind and earthquakes in the design of buildings. With the new federal requirements vis a vis wind and earthquake hazards, it is beneficial to the student to have some under­standing of the underlying concepts in this field. In addition to the class lectures, the instructor should require the student to submit a term project that includes the complete structural design of a multi-story building using standard design procedures as specified by AISC Specifications. Thus, the use of the AISC Steel Construction Manual is a must in teaching this course. In the second semester, Chapters 9 through 13 should be covered. At the undergraduate level, Chapters 11 through 13 should be used on a limited basis, leaving the student more time to concentrate on composite construction and built-up girders.

Chapters 6, 11, 12, 13, and 14 can be used for a graduate course. As a prerequisite for the graduate course, the student must have a minimum of three credit hours in the design of steel structures. The instructor will go into more depth in the presentation of Chapters 6, 11, 12, and 13. The student should be required to submit a term project using rigid frames in multi story buildings. Chapter 14 provides a simple method which can easily be computerized, allowing the student the facility of designing medium- to high-rise buildings using steel frames. U. S. customary units are used throughout, although some examples are presented with S. I. units. To help students convert from U. S. units to S. I. units, tables of conversion are provided in Chapter 1.

The allowable stress design method (ASD) is used predominantly in this book. To help the student appreciate the load and resistance factored

xiii

xiv Preface

design method (LRFD), the text includes discussions and examples utiliz­ing this method.

Fundamental principles of steel design are presented in logical order to encourage the student to tackle the problem of design with a more general perspective. Tables, graphs and other design aids are introduced to help facilitate the design process. The selection of sections in the design of composite construction is made easier by a short-cut approach, thus eliminating the tediousness of the trial-and-error method.

The author gratefully acknowledges Robert M/ Hackett of the Univer­sity of Mississippi, Joseph P. Colaco of CBM Engineers, Inc., Ramesh Malia of the University of Conneticut, and Mahesh Pendey of the Univer­sity of Waterloo, Ontario for their comments during the development of the book.

The author expresses his appreciation to the hundreds of students who have attended his classes at North Carolina Agricultural and Technical State University. Without them this book could not have been material­ized.

Finally, the author wishes to thank his wife, Dr. Mary Bentley Abu-Saba, for her continued support and encouragement.

DESIGN OF STEEL STRUCTURES