Performance assessment and parametric analysis of CFST columns with various concrete infills

This study investigated the structural behaviour of Concrete Filled Steel Tubular (CFST) columns under axial compression using two infill materials: Lightweight Concrete (LWC) and Hybrid Fibre-Reinforced Concrete (HFRC). In Phase I, the LWC mix was developed by partially replacing the fine aggregate with perlite and the coarse aggregate with pumice stone, and incorporating PVA fibres. In Phase II, the HFRC mix was developed by partial replacement of cement by flyash with the addition of Polypropylene (PP) and Coconut Fibre (CF). In Phase III, CFST column specimens filled with both LWC(CFSTLWC) and HFRC(CFSTHFRC) were experimentally tested to examine load deformation response, ductility, energy absorption, and failure characteristics. CFST columns filled with LWC demonstrated reduced self-weight while maintaining satisfactory load-carrying capacity and deformation behaviour, and CFSTHFRC columns exhibited a significant improvement in structural performance, achieving approximately 39% higher axial load capacity compared to a CFST column filled with Control Concrete (CFSTCC). A parametric study was conducted by varying diameter-to-thickness (D/t) and length-to-diameter (L/D) ratios to assess their influence on axial performance using finite element analysis. The findings highlight that an increase in (D/t) reduces the confinement and thereby reduces the load-carrying capacity, and increasing (L/D) results in an increase in buckling behaviour, which reduces the load-carrying capacity. Axial load carrying capacity of CFST columns compared with existing codal provisions. A mathematical model was also developed with L/D and (D/t), which predicted the ultimate strength ratio of CFST columns filled with LWC and HFRC, having a coefficient of correlation of 0.934 and 0.948 and validated with the experimental results existing in the literature.