Structural behavior of UHPC filled steel tube columns under axial loading

Steel tube filled with ultra-high performance concrete (UHPCFST) is an innovative and efficient structural form. To promote its application, a comprehensive experimental program was conducted to investigate the structural behavior of UHPCFST columns subjected to axial compression. The key issue is to clarify the differences in mechanical behavior between UHPCFSTs and CFSTs, and to evaluate whether the current design guidelines related to CFSTs are applicable to UHPCFSTs. To address this, the compression characteristics of UHPCFSTs were analyzed, including failure mode, load versus deformation relationship, axial compressive strength and strain development. The test results showed that the steel tube and UHPC worked well together, but the enhancement effect of the steel tube on the core UHPC strength was not as significant as that of ordinary concrete. Moreover, an experimental database of UHPCFSTs including this study was established, and the experimental results were compared with the predictions by various design codes. Based on the regression analysis of the database results, a simplified model for predicting the ultimate strength of UHPCFSTs was developed. It was concluded that the proposed model could accurately predict the axial compressive strength of UHPCFSTs with circular and square cross-sections, and was also applicable to UHPCFSTs with high-strength steel (HSS).