Mechanical performance of steel tube confined UHPC subjected to blast loading

To improve the blast resistance of concrete-filled steel tubular (CFST) and take full advantages of superior compressive strength and energy dissipation capacity of UHPC, the explosion test and numerical simulation of steel tube confined UHPC (STCU) columns were carried out. The dynamic response characters including the overpressure-time history curves, displacement-time history curves, and failure modes of the test specimens were measured. The test results indicated that the STCU columns primarily exhibit overall bending failure under blast loading without significant local buckling or cratering observed. To further investigate the blast response of the STCU columns, the finite element model incorporating S-ALE algorithm for fluid-structure interaction modelling was established and validated by the test data. The influence of slenderness ratio, axial compression ratio, scaled distance, and pre-damage degree on the blast response was systematically analyzed. Results show that peak displacement increases with the slenderness ratio (27.71–103.93) and axial compression ratio (above 0.34), while it decreases as scaled distance increases (0.19–1.86 m/kg^1/3). Pre-damage significantly amplifies the displacement amplification factor (DAFδ) under secondary blast loading when the initial scaled distance Z₁ < 0.5 m/kg^1/3. The failure mode transitions from local buckling at very small scaled distances (0.19–0.32 m/kg^1/3) to overall bending at larger distances (0.46 m/kg^1/3). These findings clearly demonstrate how both structural parameters and loading conditions jointly govern the blast resistance and dynamic behavior of STCU columns. © 2026 Elsevier Ltd.