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Posted by MSC on January 2, 2009 at 12:31 PM.
The following papers appear in the first quarter 2009 issue of AISC’s Engineering Journal. EJ is available online (free to AISC Members) at www.aisc.org/epubs.
Optimum Flexural Design of Steel Members Utilizing Moment Gradient and Cb
Flexural strength of members based on the limit state of lateral-torsional buckling is a function of the moment gradient of the unbraced length under consideration. Bending modification factor, Cb, accounts for the shape of the moment gradient within the unbraced length and allows for adjustment of the member flexural strength, possibly increasing it by a considerable amount. Therefore, neglecting the impact of Cb on member strength may lead to over-design. This paper discusses application of Cb to design of members subjected to bending including beams as well as members subjected to combined loading (compression and bending, tension and bending, or biaxial bending). Numerical examples are presented using both ASD and LRFD methods.
Topics: Beams and Flexural Members, Stability and Bracing, Combined Loading
Design Aids for Built-Up I-Shaped Beams with Slender Webs
Paul P. Nasados, Jr.
Available Strength Tables for I-shaped beams with slender webs for the limit states of flexure and shear are presented. The tables were prepared in a format similar to the design aids available in the 13th edition AISC Steel Construction Manual. The generation, applicability and limitations of the tables are discussed. An example is presented to demonstrate the usage of the Available Strength Tables.
Topics: Beams and Flexural Members, Built-Up Members, Stability and Bracing
A Model Specification for Stability Design by Direct Analysis
R. Shankar Nair
This paper presents a model specification for stability design by direct analysis. It is based on the stability provisions of the 2005 AISC Specification, rewritten around the Direct Analysis Method alone. The material is presented in the language and format of the AISC Specification, including “User Notes” and the italicizing of terms listed in the glossary where they first appear in a section. The focus on a single method has offered the opportunity to expand some of the provisions beyond what is in the current AISC Specification, both to improve clarity and to address issues that have arisen from use of the document. Where this involved substantive changes, they are explained in an appendix to this paper (Appendix A). A second appendix (Appendix B) outlines the purpose or physical significance of each of the important steps in the Direct Analysis Method by showing the correlation of these steps to the basic requirements for design of structures for stability. The “traditional” Effective Length Method is included in the correlation to show how that method differs from the Direct Analysis Method. A third appendix (Appendix C) provides guidance to the user on the modeling of structures for the application of the Direct Analysis Method.
Topics: Analysis, Specifications
The Effect of Selected RFI Variables on Steel Fabrication Performance
Thomas M. Burns
The steel fabrication process depends upon documentation that is often in need of clarification due to issues involving completeness and coordination. Clarification is obtained by the steel fabricator through the request for information (RFI) process, which allows the shop drawing production process to continue forward. The volume of requests for information sought, as well as time required to receive clarification, are just two of many variables that may influence shop drawing production as well as subsequent fabrication activities. This research identifies specific RFI variables and their significant relationship with shop drawing production and fabrication duration performance. Data from 48 projects were collected from steel fabricators throughout the United States. Regression techniques identified two variables, the RFI performance indicator and the average RFI response time, as significant predictors for both shop drawing production and fabrication duration performance measures. Within the 48 projects studied, approximately 25% of the performance variability in shop drawing production was explained by these two variables. The generalized model developed from these results may be applied by individual steel fabricators interested in performance improvement through RFI management. Project databases using RFI metrics could benefit fabricators by establishing performance thresholds while also providing engineers with a quality service indicator.
Topics: Fabrication, Quality Assurance and Control, Economy (Cost)
Current Steel Structures Research
Current Steel Structures Research
This regular feature of the Engineering Journal provides information on new and ongoing research around the world. In the 17th installment, research projects are summarized on the following topics: Sustainability of Steel Structures (University of Coimbra, Coimbra, Portugal), Seismic Design and Analysis of Rectangular Concrete-Filled Steel Tube Members and Frames (University of Illinois, Urbana, Ill.), Market Opportunities for Innovative Fastening Solutions for Steel Structures (University of Coimbra, Coimbra, Portugal), Size Effects in the Fatigue Behavior of Tubular Bridge Connections (Federal Institute of Technology, Lausanne, Switzerland), A Methodology for an Integral Life Cycle Analysis of Bridges in View of Sustainability (University of Coimbra, Coimbra, Portugal), and Load Rating of Curved Composite Steel I-Girder Bridges through Load Testing with Heavy Trucks (University of Minnesota).