Axial compression experiment and numerical simulation of CFST short columns at an ultra early age

To study the axial compression performance of ultra-early-age concrete-filled steel tube (CFST) short columns, axial compression tests were carried out on short columns of CFSTs with different wall thicknesses of steel tubes and different concrete ages. The load-displacement curves and failure modes of CFST short column specimens under different concrete ages were obtained. The influence of wall thickness and concrete age on the mechanical properties of ultra-early-age CFST specimens was analyzed. The calculation formula for the bearing capacity of mature CFST short columns in GB50936-2014 was extended, and a new calculation formula for calculating the bearing capacity of ultra-early-age CFST short columns was proposed. Considering that there is no known concrete stress-strain expression for ultra-early-age CFST short columns in existing literature, this paper has adjusted the constitutive model of the core concrete in ordinary CFSTs and advanced a stress-strain relationship suitable for the core concrete in ultra-early-age CFST short columns.