Effects of material strengths on failure modes and post-peak behaviour of high-strength concrete-filled high-strength steel tubular columns

This study presents an experimental investigation on the failure modes and post-peak behaviour of concrete-filled steel tubular (CFST) columns with different high-strength material combinations. The effects of high-strength materials on the failure modes and post-peak behaviour have been carefully addressed through the DIC-based strain/stress analysis. A total of eight short columns, designed with varying material strength combinations, were tested to examine their failure modes, axial load-displacement relationships and stress development. The results showed that high-strength materials in CFST members would generate severe shear failure modes and limited post-peak behaviour. The Digital Image Correlation (DIC)-based strain extraction method and elastic-plastic analysis were particularly employed to accurately quantify the stress development of the steel tube and core concrete during the entire loading process, with the effectiveness of existing matching criteria for material strengths revealed. The accuracy of existing calculation approaches for predicting the peak stress, peak strain of confined concrete, and the compressive bearing capacity of circular CFST columns with different material strength combinations was addressed, with design suggestions proposed eventually.