Axial compression behavior of UHPC filled square high strength steel tube after high-temperature firefighting water cooling: Experiment, numerical and calculation method

Investigating the axial compression performance of ultra-high-performance concrete-filled square high strength steel tube (UHPCFSHSST) columns after high-temperature water cooling is essential for the safety assessment and sustainability of structures after fire suppression. Therefore, this study assessed the axial compressive mechanical properties of UHPCFSHSST columns through material performance after high-temperature water cooling and 13 axial compression tests. This was achieved through using multi-factor quantitative analysis of the maximum experienced temperature (25℃-600℃), steel tube thickness (4–6 mm) and section size (100 2 mm 2 -150 2 mm 2 ). The experimental results suggest that compared to normal temperature conditions, the strength of both UHPC and high-strength steel tubes increase first and then decrease following high-temperature cooling. The cube compressive strength of UHPC and the yield strength of steel increased by as much as 11.02% and 8.34%, respectively. As the temperature rose, the peak strain of the components increased, stiffness decreased, ductility improved, and the peak load initially increased and then decreased. Furthermore, variation in steel tube thickness and section size had no significant impact these trends. Subsequently, based on experimental and expanded databases, a numerical model for UHPCFSHSST after high-temperature cooling was established, followed by a comprehensive parameter expansion analysis. Finally, a method for calculating the load-bearing capacity of such structures after high-temperature cooling was proposed. This method fully considers the influence of high temperature and rapid cooling on the effective lateral confining pressure and axial stress in the steel tube. It provides a reliable theoretical tool for the rapid assessment of structural performance after firefighting water cooling in engineering practice. • Axial compression of UHPCFSHSST columns after high-temperature water cooling was experimentally studied. • High-temperature water cooling notably alters structural performance and failure modes. • Temperature, steel tube thickness, and section size have independent effects on axial compression behavior. • A finite element model for UHPCFSHSST columns after high-temperature cooling was established. • A calculation method for ultimate bearing capacity of UHPCFSHSST columns under high temperature and cooling was proposed.