Transverse impact behavior of concrete filled steel tube simply supported members stiffened with encased I-shape CFRP

Concrete-filled steel tubular simply supported members stiffened with encased I-shaped CFRP (CFSTS-CFRP members) have been developed due to their excellent mechanical performance, promoting promising applica-tions in bridge and building structures. However, these members are susceptible to collision impacts during service, leading to serious accidents. This paper aims to investigate the structural behavior of CFSTS-CFRP members subjected to transverse impact loading, utilizing experimental, numerical, and theoretical studies. Drop hammer impact tests were conducted on three CFSTS-CFRP specimens with varying impact velocities, while a CFST specimen was used as the benchmark. The experimental results demonstrate that all CFSTS-CFRP specimens experienced bending failure. The cooperation between the I-shaped CFRP and CFST members was observed, with the mechanical properties of CFSTS-CFRP specimens being fully utilized. The working mechanism of CFSTS-CFRP members is revealed by numerical simulation results obtained from the FE models of the tested CFSTS-CFRP members, which consist of the analyses of failure mode, inertia force, sectional moment, energy absorption, etc. Furthermore, by investigating the effects of different parameters on the structural response of CFSTS-CFRP members, predicted models for dynamic flexural capacity and maximum deflection are proposed for the purpose of impact design. Additionally, the contribution of the steel tube, concrete, and I-shaped CFRP to the transverse impact resistance of CFSTS-CFRP members is clarified. This clarification provides a scientific basis for determining the respective weight coefficients in subsequent damage assessment research. The findings from the experimental, numerical, and theoretical analyses contribute to the understanding of their mechanical perfor-mance and assist in the development of more efficient design approaches.