Behavior of ultra-high-performance concrete (UHPC) encased concrete-filled steel tubular (CFST) stub columns under axial compression

A total of seventeen ultra-high-performance concrete (UHPC) encased concrete-filled steel tubular (CFST) stub columns and one normal concrete encased CFST stub column were tested under axial compression. The influence of steel fiber content, diameter of steel tube, wall thickness of steel tube and strength of core concrete on the failure mode, axial load-axial strain curve, axial compression bearing capacity and ductility of the members was experimentally investigated. Furthermore, finite element model of UHPC encased CFST stub column subjected to axial compression was established. Based on the verified finite element model, typical axial load-axial strain curve, load distribution proportion, stress development and interaction between different components of the members were analyzed in depth. Parametric studies were performed to clarify the influence of steel fiber content of UHPC, CFST ratio, wall thickness of steel tube, steel yield strength, core concrete strength and stirrup spacing on the behavior of the members. At last, a simplified formula for calculating the axial compression bearing capacity of UHPC encased CFST stub columns was proposed, which could provide reference for practical engineering applications.