Experimental Research on Flexural Performance of UHPC Encased CFSTs Under Pure Bending

Ultra-high-performance concrete (UHPC) encased concrete-filled steel tubes (CFST) have advantages such as high bearing capacity and superior durability. In order to study their flexural performance, five pure bending tests of UHPC encased CFSTs members were designed. The main parameters were the steel fiber content and the ratio of concrete-filled steel tube. Based on the experimental study, the effects of different parameters on failure mode, midspan load-deflection curves, ultimate flexural capacity, flexural stiffness, and ductility were investigated. The results showed that UHPC encased CFSTs members exhibited excellent performance. Under bending, each component could maintain good collaboration. The flexural capacity increased with the increase of the UHPC steel fiber content and the ratio of concrete-filled steel tube, especially when the steel fiber content increased from 0% to 1%, the increase in bearing capacity was particularly significant. The predictions by current codes and standards for flexural capacity of UHPC encased CFST members were 11%－38% lower than the measured ones, and the predicted flexural stiffness was generally conservative.