Axial partial compression of SSC-filled bimetallic tube stub columns: numerical study

Seawater sea-sand concrete (SSC)-filled bimetallic tubes (SSCFBT), with carbon steel outer and stainless steel inner layers, are steel–concrete composite members. A three-dimensional finite-element analysis (FEA) model is developed and validated against axial partial compression tests on circular SSCFBT columns. The comparison between the model and test results demonstrates that the FEA model accurately captures the SSCFBT members’ structural behaviour, including failure patterns, ultimate strength, load–deformation responses and bimetallic layer strain distribution. The model is then employed to investigate the underlying mechanisms governing SSCFBT columns, focusing on the composite action and stress distribution across the different components of the section. Results indicate that the SSC core bore the majority of the applied external load, and as the top end-plate thickness increased, so do the axial loads borne by the SSC core. The stress at the interface between the stainless steel tube and the SSC core is greater than that between the two tube layers. In addition, a parametric study is conducted, and the material strength shows a major effect on the ultimate strength of the CFBT members. Finally, a simplified model is proposed to predict the ultimate strength of SSCFBT stub columns under axial partial compression.