MBMAAISC Design Guide Frame Design Using WebTapered Members

1
MBMA/AISC Design Guide Frame Design Using
Web-Tapered Members

• Richard Kaehler, P.E.
• Computerized Structural Design, S.C.

2
Steel Design Guide Series 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 METAL BUILDING
MANUFACTURERS ASSOCIATION AMERICAN INSTITUTE
OF STEEL CONSTRUCTION, INC.
3
Document Goals

• Present a methodology for the design of frames
  with web-tapered members
• Practical
• Rational
• Comprehensive
• Programmable
• In accordance with 2005 AISC Specification

4
Document Emphasis

• Necessary but Minimal Theoretical Background
• Design Procedures
• Example Problems
• Practical Advice
• Extensive References to Other Work

5
Table of Contents

• 1. Introduction
• 2. Web Tapered Member Behavior
• 3. Design Basis
• 4. Stability Analysis-and-Design Requirements
• 5. Member Design
• 6. Frame Design
• 7. Annotated Bibliography
• Appendices

6
1. Introduction

• Scope and Applicability
• Basis for Recommendations
• Limitations
• Benefits of Web-Tapered Members
• Fabrication of Web-Tapered Members

7
2. Web-Tapered Member Behavior

• Previous Research
• Overview of tapered member research
• Relationship to Prior Provisions
• Overview of major differences with 1989 and
  earlier ASD Specs

8
3. Design Basis

• New AISC Terminology
• Required Strength
• Nominal Strength
• Available Strength
• Allowable Strength
• Design Strength
• Limit State Design

9
4. Stability Analysis-and-Design Requirements

• Key Terminology
• P-D P-d
• ASCE7-IBC Seismic Stability Requirements
• 2005 AISC Stability Requirements
• 2005 AISC Analysis-and-Design Methods
• Common Analysis Parameters
• aPr PeL or geLPr
• Requirements for 2005 AISC Methods

10
5. Member Design

• Key Terminology
• ge
• Axial Tension
• Axial Compression
• Flexure
• Combined Flexure and Axial Force
• Shear
• Flanges and Webs with Concentrated Forces

11
6. Frame Design

• First-Order Analysis of Frames
• Second-Order Analysis of Frames
• Analysis of Gabled Frames
• Serviceability Considerations

12
7. Annotated BibliographyReferences
13
Appendices

• A. Calculating ?eL or PeL for Tapered Members
• For both DM and ELM
• B. Calculating In-Plane ?e Factors for the ELM
• C. Benchmark Problems
• First-Order Accuracy
• Second-Order Accuracy
• In-Plane Flexural Buckling Accuracy

14
Beam Design

• LTB Strength
• One LTB Strength Ratio Calculated per Unbraced
  Length
• Cb based on Flexural Stress, not Moment
• AASHTO Cb
• Calculate Critical Stress, FeLTB, using Midspan
  Properties
• Find Controlling Ratio of Mr/Mn

15
Column Design

• In-Plane Strength
• One In-Plane Strength Ratio Calculated per Member
• For DM, Calculated from PeL
• For ELM, Calculated from Pcr
• Find Controlling Ratio of Pr/Pn

16
How do I Calculate K?

• You Dont - Use alternate expressions for Fe

17
Method of Successive Approximations

• Practical method to determine elastic in-plane
  buckling load (or multiplier) of tapered column
  with any loading pattern
• Presented in detail in Timoshenko and Gere -
  Theory of Elastic Stability, Section 2.15
• Adaptable to Spreadsheet and/or Procedural
  Programming

18
Column Design

• Out-of-Plane Strength
• One In-Plane Strength Ratio Calculated per
  Unbraced Length
• Calculated based on Midspan Properties (approx.
  the same)
• Flexural Buckling
• Flexural-Torsional Buckling
• Torsional Buckling
• Constrained-Axis Torsional Buckling
• Find Controlling Ratio of Pr/Pn

19
Combined Strength

• Using AISC combined strength equations
• Combine Maximum Ratios of Pr/Pn and Mr/Mn
• Stress based alternate format
• Divide Required and Available Strength by Same
  Section Property
• Combined Tensile and Flexural Rupture Equation

20
Tension - Shear

• Tension - usual AISC checks at critical
  cross-sections
• Shear Buckling Strengths from Falby and Lee
• based on Average a/h and h/tw values
• Tension field and non-tension field equations

21
Example Problems

• Detailed Examples of
• Tension
• Compression
• Flexure
• Shear
• Combined
• Tension and Flexure
• Compression and Flexure

22
Thank You!