Advanced Analysis of Steel Frames

Theory, Software, and Applications

W.F. Chen

• Publisher: CRC Press
• Year: 2018
• ISBN:
  9781351086417
• Edition: 1
• Topic: Technology & Engineering
• Subtopic: Civil Engineering
• Index: Technology & Engineering

The development of the limit state approach to design in recent years has focused particular attention on two basic requirements: accurate information regarding the behavior of structures throughout the entire range of loading up to the ultimate strength, and simple practical procedures to enable engineers to assess this behavior. This book satisfies these requirements by providing practical analysis methods for the design of steel frames. The book contains a wide range of second-order analyses: from elastic to inelastic, rigid to semi-rigid connections, and simple plastic hinge method to sophisticated plastic-zone method. Computer programs for each analysis are provided in the form of a floppy disk for easy implementation. Sample problems are described and user's manuals are well documented for each program developed in the book.

1: Trends Toward Advanced Analysis

J. Y. Richard Liew, Department of Civil Engineering, National University of Singapore, Singapore

W. F. Chen, School of Civil Engineering, Purdue University, West Lafayette, Indiana

1.1 Introduction

Since the publication of the two-volume book on Theory of Beam-Columns (Chen and Atsuta, 1976 and 1977), and the subsequent books and monograph related to Stability Design of Frames (Chen and Lui, 1986 and 1991; SSRC, 1992), our understanding of certain aspects of the behavior and design of steel members and frames has increased considerably and many extensions and advancements have been made during the past 10 years.

The advent of limit-states specifications has resulted in more explicit and more rational consideration of the combined effects of inelasticity and stability at maximum strength levels. Since limit-states design is based directly on factored loads and limits of resistance, it is expected that structural systems and their members will behave nonlinearly before their capacity is reached. Of course, the most direct approach for structural design is to model all the significant nonlinear effects in the analysis. However, until recently, rigorous consideration of system as well as member strength and stability in the analysis of large-scale structural system were not feasible and practical. As a result, contemporary specification provisions have been based primarily on simpler methods of analysis and member interaction equations which account approximately for the interaction of strength and stability between the member and structural system.

Recently, the advancement in computer hardware, particularly in the computing and graphics performance of personal computers and workstations, is making advanced methods of analysis more and more feasible for design use. This advancement has made it possible for the engineer to adopt the limit-states design philosophy in a wider perspective. Advanced analysis techniques hold the promise of more realistic prediction of load effects and overall structural performance, and therefore in certain cases, yield greater economic and more uniform safety. The two task groups in the U.S. — the American Institute of Steel Construction (AISC) Technical Committee 117 on Inelastic Analysis and Design and the Structural Stability Research Council (SSRC) Task Group 29 on Second-Order Inelastic Analysis for Frame Design — are working toward the implementation of advanced analysis for practical design use. Similar developments also have been observed worldwide including contributions from several specification committees such as Australia (AS4100, 1990) and Europe (EC 3, 1990), among others.

Advanced analysis is referred to any method of analysis that sufficiently represents the strength and stability behavior such that separate specification member capacity checks are not required. In recent years, there has been an intense interest in the development of advanced analysis methods suitable for design use. However, the current state-of-the-art of advanced analysis is still largely fragmented and disjointed. This book, which consists of seven chapters, is a compendium of research papers and reports, and computer programs specially catered for engineers and researchers who want to improve their knowledge and to explore the use of advanced analysis techniques for frame design. The main purposes of the book are to report the recent development in advance analysis and to provide educational type of computer software for engineers to perform planar frame analysis for a more realistic prediction of system’s strength and stability.

This chapter presents a succinct encapsulation of various analysis approaches for frame design ranging from simplified member-by-member design approach to more sophisticated computer-based analysis/design approach. Its aim is to provide a smooth transition from the current state-of-the-art knowledge on the analysis and design of steel frames to upcoming new technology and developments in engineering practice. Finally, trends and directions of advanced analysis in steel building design are identified and addressed.

1.2 Design Formats

The steel building design specifications in the U.S. has undergone a metamorphosis from the Allowable Stress Design (ASD) approach through the Plastic Design (PD) approach to the present stage of the Load and Resistance Factor Design (LRFD) approach. One fundamental feature that demarcates the LRFD approach to steel design from ASD and PD approaches is that it is a probability based design methodology that uses statistical evidenec and reliability theory to prove the logistic and rationale of the design. Design considerations are guided by the identification of a set of limit states. A design is considered acceptable if none of the limit states is violated. Since a probabilistic mathematical model was used in the development of the load and resistance factors, it is possible to give proper weight to the degree of importance for each load effect and resistance. The design based on this approach often yields a greater economic and more uniform margin of safety.

Recently, an emerging technology called advanced analysis has been proposed. This analysis approach has the potential to unlock the power of the computer for direct assessment of system and member strength and stability without the need of specification member capacity checks. The advanced analysis approach and the various design approaches upon which current practice is based are discussed separately in the following sections.

1.2.1 Allowable Stress Design (ASD)

Under the ASD philosophy, a design is said to be satisfactory if the stresses computed under service loads (or working loads) do not exceed some predesignated allowable values. It has the format of

$\frac{R_n}{F.S}\ge {\displaystyle \sum Q_{ni}}$

(1.1)

where

R_n = nominal resistance of the structural member expressed in units of stress;

Q_n = nominal working stresses computed under working load conditions;

F.S = factor of safety;

i = type of load (i.e., dead load, live load, and wind load, etc.);

n = number of load types.

These so-called allowable stresses are usually calculated by dividing either the yield or ultimate stress of the material by a safety factor. The left-hand side of Eq. (1.1) represents the allowable stress of the structural member or component under various loading conditions (e.g., tension, compression, bending, and shear). The right-hand side of the equation represents the computed combined stresses produced by various load combinations (e.g., dead load, live load, and wind load). The stress computation is based on a first-order elastic analysis, and any geometrical nonlinear effects are implicitly accounted for in the member interaction equations. However, one should realize that, in ASD, the factor of safety is applied to the resistance term, and safety is evaluated in the service load range.

1.2.2 Plastic Design (PD)

Under the PD philosophy, a design is said to be satisfactory if the load effects computed based on factored load combinations do not exceed the plastic resistance of the structural member or component. It has the format of:

$R_n\ge \gamma {\displaystyle \sum _{i=1}^n{Q}_{ni}}$

(1.2)

where R_n is the nominal plastic strength of the member, and γ is a load factor.

The load factor γ is taken as 1.7 in AISC (1978, 1989) if the nominal load effect Q_ni consists of only dead and live gravity loads, or as 1.3 if Q_ni consists of dead and li...

Table of contents

• Cover
• Half Title
• Title Page
• Copyright Page
• Table of Contents
• 1 TRENDS TOWARD ADVANCED ANALYSIS
• 2 SECOND-ORDER ELASTIC ANALYSIS OF FRAMES
• 3 SEMI-RIGID CONNECTIONS
• 4 SECOND-ORDER PLASTIC HINGE ANALYSIS OF FRAMES
• 5 PLASTIC-ZONE ANALYSIS OF BEAM-COLUMNS AND PORTAL FRAMES
• 6 PLASTIC-ZONE ANALYSIS OF FRAMES
• 7 BENCHMARK PROBLEMS AND SOLUTIONS
• Index