Effective Width Criteria for Composite Beams

A key factor in the analysis and design of composite flexural members is the effective width of the slab, i.e., that part of the slab that can be relied upon to act compositely with the steel beam. The current design specification for steel building structures in the United States3 gives detailed criteria, as do others. However, these have mostly been developed on the basis of analyses and tests of composite beams without steel deck. It is the purpose of this paper to evaluate the performance of some of the current effective width criteria, and to recommend practical improvements for use in future specifications. Some of the current design criteria that are used to determine the effective width of the slab of composite beams will be evaluated. The results include an examination of the deflection characteristics of composite beams with formed steel deck, including a comparison of theoretical and experimental data. Since only service load deflections have any practical, design-oriented value, the study has been limited to that range of response. For all practical purposes, composite members behave elastically under these conditions. The investigation also examines the influence of the various parts of the steel deck and makes recommendations for design usage.