The influence of structural and geometric imperfections on the LDB strength of steel-concrete composite beams

The behavior of structural steel frames is significantly influenced by the presence of structural and geometric imperfections. The structural imperfections, namely, the residual stresses, are generated during most manufacturing processes involving material deformation, heat treatment, machining or processing operations. As the residual stresses, the geometric imperfections are fundamental in the analysis of critical buckling and post-buckling behavior of thin-walled structures. These initial imperfections can be captured using the second order inelastic analysis, also known as advanced analysis. In the modern steel design codes, e.g., European code EC3, Australian code AS4100, North American Code AISC360-16 and Chinese code GB50017 the development of advanced numerical analyses is allowed to predict the behavior of steel and composite frames. However, the random nature of the shapes and magnitudes of the initial imperfections results in difficulties in developing these analyses. Therefore, this paper presents an assessment of the influence of structural imperfections, namely, the residual stresses, and geometric imperfections on the Lateral Distortional Buckling (LDB) strength of steel-concrete Composite Beams (SCCB). The basis of the research is a thorough comparison between numerical and experimental results. Several residual stress patterns found in the literature have been implemented in numerical simulations of four different tests on SCCB subjected to uniform hogging moment. In addition, a sensitive analysis of the geometric imperfection values, namely, the initial bending, was developed. The post buckling numerical analyses were developed with the ABAQUS software. The analysis shown in this work shall help the choice of the initial imperfections on future numerical simulations on SCCB.