Experimental and numerical investigations of UHPFRC-filled circular steel tubular columns under axial and lateral cyclic loads

This study investigates the seismic performance of ultra-high-performance fiber-reinforced concrete (UHPFRC)-filled circular steel tubular columns through experimental testing and numerical simulation. Eight specimens were tested under combined axial and lateral cyclic loading, considering three concrete types (normal-strength concrete, high-strength concrete, and UHPFRC), two steel tube thicknesses (2 mm and 5 mm), and two axial load levels (5% and 25%). Failure modes, hysteretic behavior, load-carrying capacity, stiffness, ductility, and energy dissipation were evaluated. The results demonstrate that UHPFRC-filled columns exhibit superior performance, with 91.5% and 31.5% higher load-carrying capacity compared to normal-strength and high-strength concrete-filled columns with 2 mm tube thickness, respectively. Energy dissipation improved by 101% and 24% for the same comparisons. The use of UHPFRC enables steel savings of up to 71% while achieving comparable or superior lateral capacity. A validated finite element model incorporating confinement effects and cyclic material behavior is proposed for predicting column performance.