UHPC-encased CFST composite columns under lateral impact: An experimental investigation

This study presents experimental investigations into the performance of Ultra-High Performance Concrete (UHPC)-encased Concrete-Filled Steel Tube (CFST) composite columns (UECCs) under lateral low-velocity impact loading. A comprehensive set of 12 UECC specimens was meticulously constructed, taking into account varying factors such as steel fiber contents in UHPC, inner steel tube diameters, steel rebar reinforcements, and impact velocities. The dynamic response of UECCs during impact, including detailed analyses of impact force and displacement time histories, as well as post-impact failure modes, was thoroughly examined. Results highlight the superior impact resistance of UECCs compared to conventional concrete-encased UHPC columns (CECCs), attributed to effective collaboration between UHPC and CFST, coupled with UHPC's exceptional impact performance characteristics. Steel fiber content significantly influences impact behavior, with higher contents leading to increased impact force and reduced displacements. Impact force shows a linear relationship with velocity, while variations in steel tube diameter demonstrate minimal effects on overall performance. Steel rebar reinforcement proves critical in enhancing UECCs' resistance to impact, resulting in reduced displacements and enhanced energy dissipation capabilities. Additionally, a simplified predictive model was proposed, facilitating efficient design processes by predicting dynamic displacement using only initial kinetic energy and static force capacity. This model accurately distinguishes between various reinforcement configurations and aligns with findings from literature. Finally, a simplified demand-capacity design approach considering both ultimate capacity and performance levels, were proposed for the designing of UECCs under lateral impact.