Local and Postlocal Buckling of Fabricated Steel and Composite Cross Sections

Composite sections are being increasingly used as columns in multistory buildings. These sections provide considerable economy as they eliminate plywood formwork and allow large percentages of steel to be utilized in their application. The initial local buckling load of these sections is enhanced by the presence of the concrete infill and this allows very slender steel plates to be used in their fabrication. This paper investigates the local and postlocal buckling behavior of welded sections as box or wide flange I-sections. An extensive set of experiments was conducted on both hollow and concrete-filled steel box sections. Furthermore, a detailed study of flange outstands with and without concrete infill is considered in this paper. A numerical model based on the finite strip method is used to determine the initial local buckling stress incorporating residual stresses, and this is shown to agree well with the experiments. Finally, an effective width model developed elsewhere and presented in existing international codes is augmented and calibrated with the test results. This method is found to be useful in determining the axial compressive strength of these cross sections.