Bending performance analysis and crack width calculation of ultra-high-performance concrete beams

In this study, four-point bending tests were carried out on six ultra-high-performance concrete (UHPC) and three normal concrete (NC) beams. The mechanical performance and development mechanism of cracks in UHPC beams were investigated. The concrete type and longitudinal reinforcement ratio were selected as test parameters. The bending capability, vertical deflections, and crack evolution of the beams were evaluated. The results implied that UHPC beams had more fine cracks and exhibited excellent integrity and recoverability owing to the bridge action of steel fibers. The characteristic loads (cracking, yield, and ultimate loads) and ductility of the UHPC beams were superior to those of the NC beams. As the longitudinal reinforcement ratio increased, the crack spacing and crack widths of beams all decreased. Furthermore, an approach to determine the max crack width in UHPC beams was proposed based on the synergistic force and deformation coordination among the reinforcement and UHPC. Formulas for calculating the stress of the reinforcement and crack spacing of UHPC beams were established, considering the tensile behavior of steel fibers in the cracked section. Combined with the test data and the results presented in the literature, the crack widths of these UHPC beams were determined using the proposed formula and the French standard NF P 18-710 (2016), respectively. The model outcomes were all in excellent accordance with the test results.