Performance of concrete-encased CFST subjected to low-velocity impact: shear resistance analysis

Abstract

The performance of concrete-encased concrete-filled steel tube (concrete-encased CFST) subjected to low-velocity impact is investigated through experimental and numerical studies in this paper. A total of 40 concrete-encased CFST specimens, 20 square and 20 circular ones, are tested under a drop hammer apparatus. It shows that while the outer RC components have a shear-dominated failure mode, the core CFST deforms in a flexural pattern. The influence of tested parameters on the impact force and midspan deflection of the specimens is summarized. A finite element analysis (FEA) model is then established to investigate the shear mechanism of concrete-encased CFST under impact. A comparative study between a concrete-encased CFST member and an RC member shows that the core CFST component could effectively mitigate the shear failure of the outer RC section under impact due to its high shear resistance; meanwhile, the outer RC component could well protect the core CFST and reduce its flexural deformation. Such composite effects make the concrete-encased CFST a desirable impact-resisting structure. Subsequently, a parametric study on the impact velocity shows that the debonding between outer RC and core concrete can be more prominent for the impact with a relatively higher velocity, and the use of shear studs is suggested for members under such circumstances.