Residual axial compressive behavior of UHPC-filled high-strength square steel tubular members after lateral impact

Abstract

Extreme loads, such as impacts and explosions, can cause significant damage to structural components. It is crucial to thoroughly examine the residual bearing capacity of structures subjected to these extreme loads, which will enable engineers to make informed recommendations regarding repairs or reinforcements, thereby preventing further damage and extending the lifespan of these structures. This study presented an experimental and numerical investigation into the residual behavior of ultra-high-performance concrete-filled high-strength square steel tube (UHPC-FHST) members after lateral impact. A total of 15 tests were conducted, including lateral impact tests using a drop hammer testing machine and subsequent axial compression tests using a hydraulic testing machine. Of these, 12 specimens were subjected to impact loading followed by residual capacity assessment, while three intact specimens served as control groups during the axial compression tests. The failure modes, residual bearing capacity, and load-displacement curves of the specimens were obtained. Based on the experimental results, parametric analyses were performed to examine the effects of the yield strength of the steel tube, tube thickness, impact location, and impact energy on the residual mechanical performance of specimens (i.e., residual lateral deformation, residual axial bearing capacity, and residual ratio). The results showed that UHPC-FHST specimens exhibited excellent resistance to lateral impact, retaining a large level of residual bearing capacity after impact; increasing the yield strength and thickness of the steel tube effectively reduces residual deformation, and significantly enhances its residual capacity and energy absorption capacity; overall flexural failure and following second-order effects weakened the residual capacity of mid-span impact specimens, and shear failure and crack propagation of concrete were the main causes of damage for end impact conditions. Finally, a finite element (FE) model was also developed and validated using the experimental data. The established FE model demonstrated good agreement with the test results, offering a solid theoretical basis for further research on the residual performance of UHPC-FHST members subjected to lateral impact.