Local and post-local buckling of normal/high strength steel sections with concrete infill

Abstract

Steel sections in steel-concrete composite columns have been proofed to be less susceptible to local buckling and have higher capacity than bare steel columns, attributed to the internal restraints provided by the infilled concrete. This article presents a theoretical study concerning the local and post-local buckling of fabricated normal and high strength steel sections filled with concrete, including concrete filled steel tubular (CFST) sections and partially encased composite (PEC) sections. A nonlinear finite element (FE) model was established and validated to simulate the behavior of steel plates in contact with concrete, with both geometric imperfections and residual stresses explicitly incorporated. This model was subsequently applied in a parametric study to investigate the effects of several critical factors on the local buckling behavior of box and I steel sections. Based on the available test and FE results, new design formulas were proposed to predict the local buckling and post-buckling ultimate strengths of concrete-restrained steel box and I sections, taking into consideration high material strengths, residual stresses and geometric imperfections. The enhancement of strength due to the presence of concrete infill was confirmed through a comparison with the post-buckling strength of bare steel sections. Recommendations were also made for design purpose based on the formulas proposed.