Tests and analysis on circular UHPFRC-filled steel tubular stub columns under eccentric compression

Abstract

This paper developed the circular ultra-high performance fiber-reinforced concrete (UHPFRC)-filled steel tubular stub columns (CUFTSCs) for buildings and bridge piers. Eccentric-compression behaviours of CUFTSCs were studied through a 16-test program, and the studied key influencing parameters were eccentricity ratio (e/r = 0.0, 0.30, 0.68, and 0.98) and thickness of steel tube (ts). Under eccentric compression, the CUFTSCs failed in flexure-governed mode and exhibited linear, nonlinear, and recession working stages. The nonlinearities of CUFTSCs under eccentric compression were mainly contributed by nonlinear mechanical behaviours of compression steel tube and UHPFRC and minor steel-tube local buckling. UHPFRC crushing and major steel-tube local buckling occurred to the peak load point and recession branch of N-Δ/N-δ curves of CUFTSCs, respectively. As the eccentricity ratio increases the failure mode of CUFTSCs gradually changed from the compression-governed mode to flexural-bending-governed mode. The ductility of CUFTSCs is significantly improved through using thick steel tube. The code equations in EC4, AISC and GB50936 were conservative on predicting Nu-Mu interaction curves of CUFTSCs due to the ignorance of tensile strength of UHPFRC. The developed analytical models offer the most accurate estimations on Nu-Mu interaction curves of CUFTSCs.