Behaviour of axially loaded circular concrete-filled bimetallic stainless-carbon steel tubular short columns

Circular concrete-filled bimetallic steel tubular (CFBST) columns are considered as a new type of structural composite members. An experimental investigation has recently been conducted on the performance of these concentrically-loaded circular CFBST stub columns. However, the fundamental response of these columns under axial compression has not been investigated numerically. Therefore, finite element (FE) analysis of axially loaded circular CFBST stub columns is discussed in this paper. An existing concrete constitutive model with the confinement mechanism is modified for the current CFBST columns. The nonlinear stress-strain relationship of stainless steel is utilised in the FE analysis. The current FE model accounts for the influences of initial imperfections, geometric and material nonlinearities. The ultimate strengths and load-strain responses predicted from the analysis are validated against the available test results and observations in literature. The comparisons indicate that the FE model accurately estimates both the ultimate strengths and load-strain characteristics of the concentrically-loaded circular CFBST stub columns. The developed model is then utilised to investigate the effects of the geometric configurations and material properties on the load-strain characteristics, ultimate capacity, ductility and steel contribution ratio of circular CFBST stub columns. The existing design recommendations for conventional circular concrete-filled steel tubular columns are then checked for computing the peak load of the circular CFBST stub columns, and the best strength predictor with the least deviation compared with the experimental values is recommended at the end for design.