Performance of concrete-encased CFST box stub columns under axial compression

A finite element analysis (FEA) model is developed to predict the full range response of concrete-encased CFST box stub columns under axial compression. In the model, concrete across the composite section is divided into four regions, i.e. the outer unconfined concrete outside the stirrup, the outer concrete in the web walls, the outer confined concrete in the corners, and the core concrete in the steel tubes. Different material models are used in each region. The analytical results are compared to past experiments, and generally good agreement between the predicted and measured results is obtained. Load-axial strain, loading distribution between the inner CFST and outer RC components and interface stresses between steel and concrete are analyzed. The influence of the web wall slenderness is also investigated. Parameter studies investigate the influence of concrete and steel strength, steel ratio of CFST, longitudinal bar ratio, stirrup spacing and ratio of the diameter of CFST to the sectional width on the ultimate load. A simplified model is proposed to predict the ultimate load of the concrete-encased CFST box stub columns under axial compression.