AISC Design Guide 25 - Frame Design Using Web-Tapered Members-www.civilstars.com.pdf - 25 Steel Design Guide Frame Design Using Web-Tapered Members 25

AISC Design Guide 25 - Frame Design Using Web-Tapered Members-www.civilstars.com.pdf

This preview shows page 1 out of 225 pages.

You've reached the end of your free preview.

Want to read all 225 pages?

Unformatted text preview: 25 Steel Design Guide Frame Design Using Web-Tapered Members 25 Steel Design Guide Frame Design Using Web-Tapered Members RICHARD C. KAEHLER Computerized Structural Design, S.C. Milwaukee, Wisconsin DONALD W. WHITE Georgia Institute of Technology Atlanta, Georgia YOON DUK KIM Georgia Institute of Technology Atlanta, Georgia A ME RICAN INSTITUT E OF S T E E L CONS T RUCT I O N AISC © 2011 by American Institute of Steel Construction All rights reserved. This book or any part thereof must not be reproduced in any form without the written permission of the publisher. The information presented in this publication has 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, suitability 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 information 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 incorporated 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 edition. Printed in the United States of America Authors Richard C. Kaehler, P.E. is a vice president at Computerized Structural Design, S.C. in Milwaukee, WI. He is a member of the AISC Committee on Specifications and its task committees on Stability and Member Design, and chairs its Editorial task committee. Donald W. White, Ph.D is a Professor at the Georgia Institute of Technology School of Civil and Environmental Engineering. He is a member of the AISC Committee on Specifications and its task committees on Member Design and Stability. Yoon Duk Kim, Ph.D is a postdoctoral fellow at the Georgia Institute of Technology School of Civil and Environmental Engineering. Acknowledgments The authors express their gratitude to the Metal Building Manufacturers Association (MBMA) and the American Iron and Steel Institute (AISI), who provided the funding for both the preparation of this document and the research required to complete it. The authors also appreciate the guidance of the MBMA Steering Committee: Al Harrold Allam Mahmoud Dean Jorgenson Dennis Watson Duane Becker Jeff Walsh Norman Edwards Scott Russell Steve Thomas Butler Manufacturing United Structures of America Metal Building Software BC Steel Buildings Chief Buildings American Buildings Questware Nucor Building Systems Varco Pruden Buildings Dr. Efe Guney of Intel Corporation and Mr. Cagri Ozgur of Georgia Tech provided assistance with several investigations of design calculation procedures. The authors also appreciate the efforts of the AISC reviewers and staff members who contributed many excellent suggestions. Preface This design guide is based on the 2005 AISC Specification for Structural Steel Buildings. It provides guidance in the application of the provisions of the Specification to the design of web-tapered members and frames composed of web-tapered members. The recommendations of this document apply equally to the 2010 AISC Specification for Structural Steel Buildings, although some section and equation numbers have changed in the 2010 Specification. i ii Table of Contents CHAPTER 1 INTRODUCTION...............................1 CHAPTER 5 MEMBER DESIGN ..........................31 1.1 1.2 1.3 1.4 5.1 5.2 1.5 BASIS FOR RECOMMENDATIONS .................1 LIMITATIONS ...............................................1 BENEFITS OF WEB-TAPERED MEMBERS ......2 FABRICATION OF WEB-TAPERED MEMBERS ...........................2 GENERAL NOTES ON DOCUMENT ...............3 5.3 CHAPTER 2 WEB-TAPERED MEMBER BEHAVIOR AND DESIGN APPROACHES ...............5 2.1 2.2 PREVIOUS RESEARCH .................................5 RELATIONSHIP TO PRIOR AISC PROVISIONS FOR WEB-TAPERED MEMBERS ...........................9 CHAPTER 3 DESIGN BASIS ................................ 13 3.1 3.2 KEY TERMINOLOGY ................................. 13 LIMIT STATE DESIGN ................................. 14 3.2.1 LRFD Design Basis ............................. 14 3.2.2 ASD Design Basis............................... 14 3.2.3 Allowable Stress Design ....................... 15 5.4 CHAPTER 4 STABILITY DESIGN REQUIREMENTS ................................................ 17 4.1 4.2 4.3 4.4 4.5 4.6 KEY TERMINOLOGY ................................. 17 ASCE 7 AND IBC SEISMIC STABILITY REQUIREMENTS ......................17 AISC STABILITY REQUIREMENTS ..............19 STABILITY DESIGN METHODS...................20 4.4.1 Limits of Applicability .........................21 4.4.2 Type of Analysis .................................21 4.4.3 Out-of-Plumbness ...............................21 4.4.4 Stiffness Reduction ............................. 22 4.4.5 Design Constraints .............................. 22 COMMON ANALYSIS PARAMETERS ........... 22 4.5.1 α Pr ............................................................ 22 4.5.2 PeL or γeLPr ......................................... 23 4.5.3 Δ2nd /Δ1st ............................................ 24 DETAILED REQUIREMENTS OF THE STABILITY DESIGN METHODS................... 24 4.6.1 The Effective Length Method (ELM) ...... 24 4.6.2 The Direct Analysis Method (DM) ........... 26 4.6.3 The First-Order Method (FOM)................ 29 5.5 iii KEY TERMINOLOGY ................................. 31 AXIAL TENSION ........................................ 31 5.2.1 Tensile Yielding .................................. 31 5.2.2 Tensile Rupture .................................. 31 Example 5.1—Tapered Tension Member with Bolt Holes ................................ 32 AXIAL COMPRESSION ............................... 33 5.3.1 Calculate Elastic Buckling Strength ........ 35 5.3.2 Calculate Nominal Buckling Stress Without Slender Element Effects, Fn1 ...... 36 5.3.3 Calculate Slenderness Reduction Factor, Q, and Locate Critical Section .....37 5.3.4 Calculate Nominal Buckling Stress with Consideration of Slender Elements, Fcr ...........................37 5.3.5 Strength Ratio ....................................38 5.3.6 Other Considerations ...........................38 Example 5.2—Tapered Column with Simple Bracing .............................................38 FLEXURE...................................................58 5.4.1 Common Parameters............................58 5.4.2 Compression Flange Yielding ................61 5.4.3 Lateral-Torsional Buckling (LTB) ............ 61 5.4.4 Compression Flange Local Buckling (FLB) ..........................62 5.4.5 Tension Flange Yielding (TFY) ..............63 5.4.6 Tension Flange Rupture........................63 5.4.7 Strength Ratio ....................................64 Example 5.3—Doubly Symmetric Section Tapered Beam ...................................64 5.4.8 Commentary on Example 5.3 ................82 COMBINED FLEXURE AND AXIAL FORCE ....................................82 5.5.1 Force-Based Combined Strength Equations ..............................83 5.5.2 Separate In-Plane and Out-of-Plane Combined Strength Equations ...............83 5.5.3 Stress-Based Combined Strength Equations ..............................84 Example 5.4—Combined Axial Compression and Flexure ...............................85 5.5.4 Commentary on Example 5.4 ................94 5.6 5.7 5.8 SHEAR.......................................................95 5.6.1 Shear Strength of Unstiffened Webs ........95 5.6.2 Shear Strength of Stiffened Webs Without Using Tension Field Action .......95 5.6.3 Shear Strength of Stiffened Webs Using Tension Field Ation ............96 5.6.4 Web-to-Flange Weld ............................97 Example 5.5—Shear Strength of a Tapered Member ...........................................97 FLANGES AND WEBS WITH CONCENTRATED FORCES........................ 102 ADDITIONAL EXAMPLES ........................ 102 Example 5.6—Tapered Column with Unequal Flanges and One-Sided Bracing ..................... 102 Example 5.7—Singly Symmetric Section Tapered Beam with One-Sided Bracing ........... 120 Example 5.8—Combined Axial Compression and Flexure ............................. 132 6.3 6.4 ANALYSIS OF SINGLE-STORY CLEAR-SPAN FRAMES ............................. 148 6.3.1 Behavior of Single-Story Clear-Span Frames ............................ 148 6.3.2 In-Plane Design Length of Rafters........ 148 6.3.3 Sidesway Calculations for Gabled Frames ................................. 148 SERVICEABILITY CONSIDERATIONS ....... 149 CHAPTER 7 ANNOTATED BIBLIOGRAPHY...... 151 APPENDIX A. CALCULATING γeL OR PeL FOR TAPERED MEMBERS ........................... 169 A.1 A.2 A.3 EQUIVALMENT MOMENT OF INERTIA ..... 169 METHOD OF SUCCESSIVE APPROXIMATIONS ................................... 170 EIGENVALUE BUCKLING ANALYSIS ........ 172 CHAPTER 6 FRAME DESIGN ........................... 139 APPENDIX B. CALCULATING IN-PLANE γe FACTORS FOR THE ELM .............. 173 6.1 B.1 6.2 FIRST-ORDER ANALYSIS OF FRAMES ............................................. 139 SECOND-ORDER ANALYSIS OF FRAMES ............................ 140 6.2.1 P-Δ-Only Analysis ............................ 141 6.2.2 Analysis Using Elements that Include Both P-Δ and P-δ Effects in the Formulation................... 142 6.2.3 Alternative Amplified First-Order Analysis .......................... 143 6.2.4 Required Accuracy of Second-Order Analysis....................... 143 6.2.5 Stiffness Reduction ........................... 144 6.2.6 Load Levels for Second-Order Analysis....................... 144 6.2.7 Notional Loads ................................. 145 6.2.8 Explicit Out-of-Plumbness .................. 145 6.2.9 Lean-on Structures ............................ 146 B.2 B.3 COLUMNS ............................................... 173 B.1.1 Modified Story-Stiffness Method ...................... 173 B.1.2 Eigenvalue Buckling Analysis ............. 173 RAFTERS ................................................. 174 B.2.1 Eigenvalue Buckling Analysis ............. 174 B.2.2 Method of Successive Approximations .. 175 THE RELATIONSHIP BETWEEN K AND γe.................................. 175 APPENDIX C. BENCHMARK PROBLEMS.......... 177 C.1 C.2 C.3 PRISMATIC MEMBERS ............................. 177 TAPERED MEMBERS ................................ 177 METHOD OF SUCCESSIVE APPROXIMATIONS ................................... 184 C.3.1 γeL and PeL of Simple Web-Tapered Column ........................ 184 C.3.2 γeL of Stepped Web-Tapered Column ..... 187 SYMBOLS ........................................................ 193 GLOSSARY .................................................................. 197 REFERENCES ................................................... 199 iv Chapter 1 Introduction This document provides suggested methods for the design of web-tapered I-shaped beams and columns, as well as frames that incorporate web-tapered I-shaped beams and/or columns. Both the requirements for analysis and rules for proportioning of web-tapered framing members are addressed. The emphasis is on members and frames with proportions and bracing details commonly used in metal building systems. However, this information is equally applicable to similar tapered members used in conventional steel construction. The methods contained herein are primarily interpretations of, and extensions to, the provisions of the 2005 AISC Specification for Structural Steel Buildings (AISC, 2005), hereafter referred to as the AISC Specification. The recommendations of this document apply equally to the 2010 AISC Specification for Structural Steel Buildings, although some section and equation numbers have changed in the 2010 AISC Specification. These recommendations are not intended to apply to structures designed using earlier editions of the AISC Specification. The 2005 AISC Specification is a significant departure from past AISC Specifications, particularly the ASD Specifications, with which almost all metal buildings have been designed in the United States. Engineers and other users familiar with the previous ASD editions will find significant changes in the presentation of the AISC Specification, the member design provisions, and the requirements for analysis. The AISC Specification contains no provisions specific to tapered members. The methods presented in this document comply with the 2005 AISC Specification and provide additional information needed to apply the Specification to tapered members. In some instances, procedures are provided for situations not addressed by the AISC Specification. These are noted where they occur. The publication of the recommendations in this document is not intended to preclude the use of other methods that comply with the AISC Specification. 1.1 BASIS FOR RECOMMENDATIONS The following sources were used extensively in the preparation of this document, are referenced extensively herein, and should be used in conjunction with this publication for a fuller understanding of its recommendations: 1. ANSI/AISC 360-05, Specification for Structural Steel Buildings (AISC, 2005) and its commentary 2. “A Prototype Application of the AISC (2005) Stability Analysis and Design Provisions to Metal Building Structural Systems” (White and Kim, 2006) The References and Annotated Bibliography sections of this document provide references to other publications relevant to the design of tapered members and frames composed of tapered members. Additional requirements for seismic design and detailing can be found in the ANSI/AISC 341-05, Seismic Provisions for Structural Steel Buildings (AISC, 2005a). A significant research program was conducted as part of the development of this Design Guide. This research was conducted by White, Kim and others at the Georgia Institute of Technology. The focus of this work was the verification and adaptation of the AISC Specification provisions for tapered members and frames composed of tapered members. The researched topics included studies on the following: 1. Beam lateral-torsional buckling (LTB) 2. Column in-plane and out-of-plane flexural buckling 3. Column torsional and flexural-torsional buckling 4. Influence of local buckling on member resistances 5. Combined influence of local buckling and member yielding on overall structure stiffness and strength 6. Synthesis of approaches for calculation of secondorder forces and moments in general framing systems 7. Benchmarking of second-order elastic analysis software 8. Consideration of rotational restraint at nominally simply supported column bases 9. Consideration of general end restraint effects on the LTB resistance of web-tapered members The reader is referred to Kim and White (2006a, 2006b, 2007a, 2007b); Kim (2010); Ozgur et al. (2007); and Guney and White (2007) for a detailed presentation of research results for these topics. 1.2 LIMITATIONS Except where otherwise noted in the text, these recommendations apply to members satisfying the following limits: 1. Specified minimum yield strength, Fy ≤ 55 ksi. 2. Homogeneous members only (hybrid members are not AISC DESIGN GUIDE 25 / FRAME DESIGN USING WEB-TAPERED MEMBERS / 1 considered); i.e., Fyf = Fyw, where Fyf and Fyw are the flange and web minimum specified yield strengths. 3. Web taper is linear or piecewise linear. 4. Web taper angle is between 0° and 15°. 5. Thickness of each flange is greater than or equal to the web thickness. 6. Flange slenderness ratio is such that bf ≤ 18 2t f where bf = flange width, in. tf = flange thickness, in. 7. Flange width is such that h bf ≥ 7 throughout each unbraced length, Lb. Exception: if Lb ≤ 1.1 rt E Fy bf ≥ h 9 throughout the unbraced length. In the foregoing equations, h = web height, in. rt = radius of gyration of the flange in flexural compression plus one third of the web area in compression due to the application of major axis bending moment alone, calculated using the largest section depth within the length under consideration, in. 8. Web slenderness (without transverse stiffeners or with stiffeners at a/h >1.5) is such that h 0.40 E ≤ ≤ 260 tw Fy where E = modulus of elasticity, ksi tw = web thickness, in. 9. Web slenderness (with transverse stiffeners at a/h ≤1.5) is such that h E ≤ 12 tw Fy It is expected that these recommendations can be extended to homogeneous members with larger yield strengths. However, the background research for these recommendations was focused on Fy = 55 ksi, because the use of larger yield strengths is not common in current practice. In addition, it is expected that the recommendations can be extended to hybrid members. The background research for the recommendations in this Design Guide was focused on homogeneous members and the AISC Specification does not address hybrid members. Comprehensive provisions for flexural design of hybrid members are provided in the American Association of State Highway and Transportation Officials (AASHTO) LRFD Bridge Design Specifications (AASHTO, 2004, 2007). Furthermore, it is expected that the recommendations can be applied to members with parabolic or other tapered web geometries. However, calculation of the elastic buckling resistances of these types of members is beyond the scope of this document. The general approach provided in this document also accommodates members with steps in the crosssection geometry at field splices or transitions in crosssection plate dimensions. However, the primary focus of this document is on members with linear or piecewise linear web taper. 1.3 BENEFITS OF WEB-TAPERED MEMBERS Web-tapered members have been utilized extensively in buildings and bridges for more than 50 years. Design Optimization—Web-tapered members can be shaped to provide maximum strength and stiffness with minimum weight. Web depths are made larger in areas with high moments, and thicker webs are used in areas of high shear. Areas with less required moment and shear strength can be made shallower and with thinner webs, respectively, saving significant amounts of material when compared with rolled shapes. Fabrication Flexibility—Fabricators equipped to produce web-tapered members can create a wide range of optimized members from a minimal stock of different plates and coil. This can result in time and cost savings compared with the alternative of ordering or stocking an array of rolled shapes. In many cases, the savings in material can offset the increased labor involved in fabricating web-tapered members. 1.4 FABRICATION OF WEB-TAPERED MEMBERS Web-tapered I-shaped members are fabricated by welding the inside and outside flange plates to a tapered web plate. In the metal building industry, this welding is generally performed by automated welding machines. One typical process is as follows: 1. Flanges and webs are cut to size or selected from plate, coil, or bar stock, and spliced as required to length. 2. Flanges and webs are punched as required for attachments (bracing, purlin and girt bolts, etc.). 2 / FRAME DESIGN USING WEB-TAPERED MEMBERS / AISC DESIGN GUIDE 25 3. Flanges are tack-welded to the web, with the web in a horizontal position. 4. With the web in the horizontal position, both flanges are simultaneously welded to the webs from the top side only, using an automated process that proceeds along the length of the member from one end to the other. Exception: welding on both sides of the web at member ends ma...
View Full Document

  • Winter '14

What students are saying

  • Left Quote Icon

    As a current student on this bumpy collegiate pathway, I stumbled upon Course Hero, where I can find study resources for nearly all my courses, get online help from tutors 24/7, and even share my old projects, papers, and lecture notes with other students.

    Student Picture

    Kiran Temple University Fox School of Business ‘17, Course Hero Intern

  • Left Quote Icon

    I cannot even describe how much Course Hero helped me this summer. It’s truly become something I can always rely on and help me. In the end, I was not only able to survive summer classes, but I was able to thrive thanks to Course Hero.

    Student Picture

    Dana University of Pennsylvania ‘17, Course Hero Intern

  • Left Quote Icon

    The ability to access any university’s resources through Course Hero proved invaluable in my case. I was behind on Tulane coursework and actually used UCLA’s materials to help me move forward and get everything together on time.

    Student Picture

    Jill Tulane University ‘16, Course Hero Intern

Stuck? We have tutors online 24/7 who can help you get unstuck.
A+ icon
Ask Expert Tutors You can ask You can ask You can ask (will expire )
Answers in as fast as 15 minutes
A+ icon
Ask Expert Tutors