Experimental and numerical investigation on the composite columns made of prefabricated ultra-high performance concrete tube filled with normal strength concrete

This paper presents an experimental and numerical study of the structural performance of normal strength concrete (NSC) filled in ultra-high performance concrete (UHPC) tube circular columns (UHPC-NSC columns) under axial compression. The steel fibers volume fractions of UHPC and the loading methods were exprimentally investigated as main parameters. The thickness and compressive strength of UHPC tubes were subsequently evaluated using a modeling approach. Three volumes of steel fibers including 0%, 1% and 2% were adopted for UHPC mixture. Six short UHPC-NSC circular columns were tested under loading on the entire section and on only NSC core. One control circular short columns made of NSC was also tested under axial compression. The experimental results indicated that as compared to the control columns, the utimate loads of the UHPC-NSC columns are significantly increased. When volume of steel fibers increases, the ultimate load and ductility of UHPC-NSC columns increases. For UHPC-NSC columns under loading on only the NSC core, the ultimate loads of UHPCNSC columns with UHPC having fiber volume of 0%, 1% and 2% were 20.12%, 29.22% and 41.73% higher than that of the control column, respectively. For UHPC-NSC columns loaded on the entire section, the ultimate loads of UHPC-NSC columns using UHPC having fiber volume of 0%, 1% and 2% were 178.23%, 181.31% and 246.76% higher than that of the control column, respectively. The UHPC-NSC columns loaded on the entire section had ultimate load higher than those loaded on NSC core, but their ductility was lower. Finally, a finite element model (FEM) was developed to verify the test results with a good agreement. Based on the established FEM, a parametric study on the effect of the thickness and compressive strength of UHPC tube on the structural performance of UHPC-NSC columns was conducted. Deriving from the findings in this paper, UHPC can be considered as a potential material to produce thin walled tubes and to work as formworks for filling NSC.