Experimental study on residual axial bearing capacity of UHPFRC-filled steel tubes after lateral impact loading

Concrete- filled steel tube (CFST) has been widely used in civil engineering. Numerous studies have shown that concrete-filled double-skin steel tube (CFDST) columns exhibit satisfactory mechanical properties under various loading conditions. Furthermore, ultra-high performance fiber-reinforced concrete (UHPFRC) has been developed as a prominent representative of new construction materials. This study investigates the residual bearing capacities of 10 concrete-filled steel tube specimens (three CFST columns and seven CFDST columns) after impact loading. The investigated parameters include the steel ratio, the concrete type, the section form, axial load ratio, the impact energy and the presence/absence of impact load. The results demonstrate that, when the inner steel tube thicknesses are identical, increasing the steel ratio from 0.296 to 0.467 (the outer steel tube thickness increases from 5 mm to 8 mm) can effectively improve the residual performance. For the non-impacted specimens, the bearing capacity of the CFDST columns is increased by 47.1% as the concrete type is changed from NSC to UHPFRC. For the impacted specimens, due to the influence of the test setup and other reasons, the concrete type has only a slight influence on the residual performance of CFDST columns; however, it has a substantial influence on the residual performance of the CFST columns. Furthermore, with the concrete type in the CFST columns changing from NSC to UHPFRC, the residual performance of CFST columns can be significantly enhanced.