Design and evaluation methods for CFST members with high-performance materials subjected to axial impact

High-performance concrete-filled steel tube (CFST) members consisting of high-strength steel and ultra-high performance concrete (UHPC) are more and more widely applied in modern engineering structures. These structures/structural components may suffer from axial impact loading during its life cycle such as impact induced by the collapse of top-level floors. However, the design and evaluation methods for axial impact resistance remain unclear for these structures. This paper presented a systematic study on both the impact and post-impact resistances of high-performance CFST members subjected to axial impact. A database of CFST members subjected to axial impact was first compiled, and a finite element (FE) model was established and verified by the test results from the compiled database. The effects of key parameters on the impact resistances and residual capacity of square UHPC-filled high-strength steel tubes under axial impact were clarified. By employing 420 FE models of square CFST columns subjected to axial impact with random parameters, equations for predicting the maximum axial displacement under axial impact and axial residual bearing capacity after axial impact that are suitable for conventional and high-performance CFST columns (f_y ≤ 960 MPa and f_cu ≤ 200 MPa) were developed with reasonable accuracy. Finally, a maximum deformation limit was recommended for CFST components subjected to axial impact, which provides a reference for anti-impact design and evaluation for general high-performance CFST members.