Axial compressive performance of ultra-high performance concrete-filled steel tube stub columns at different concrete age

To investigate the axial compressive performance of ultra-high-performance concrete-filled steel tube (UHPCFST) stub columns at different age, the axial compressive tests of UHPC specimens and UHPCFST short columns cast in the same batch at different concrete ages were carried out. The failure mode, stress–strain curve and the key indicators such as axial strength, elastic module and peak strains of UHPC at different ages were analysed. Meanwhile, the failure patterns, load–strain curves and the evolution of ultimate bearing capacities and stiffness of UHPCFST short columns at various ages were analysed. In addition, the constitutive relationship of mature normal concrete in the Chinese standard GB50010 was extended to numerically model UHPC columns under axial compression at different ages. Meanwhile, based on the axial compressive bearing capacity of UHPCFST short columns at mature age (28 days), a formula for calculating the load bearing capacity of UHPCFST short columns at different ages was proposed by introducing the age hooping correction coefficient, and verified using both test and simulation results. This study will provide a reference for the safe construction of ultra-high performance concrete-filled steel tubes.