Experimental investigation on flexural and ductile behaviors of rebar-reinforced ultra-high-performance concrete beams

This paper experimentally investigated the flexural and ductile behaviors of ultra-high-performance concrete (UHPC) beams. The failure modes, deflection, ductility, concrete strain, and reinforcement strain were tested using eight UHPC rectangular beams. The experimental parameters were the reinforcement ratio, the reinforcement diameter, and the UHPC cover thickness. The experimental results showed that all specimens exhibited flexural failure characterized by the yielding of steel rebars, multiple micro-cracks, one localized macro-crack, and slight crushing of UHPC. It was concluded that increasing the reinforcement ratio significantly enhanced the stiffness, flexural capacity, and ductility of the rebar-reinforced UHPC beams, whereas showed little effect on their cracking load. Meanwhile, both the reinforcement diameter and UHPC cover thickness in the range investigated here had little influence on the flexural performance of UHPC beams in the elastic stage and crack development stage, whereas exhibited different influences in the yield stage. Besides, increasing the reinforcement ratio was in favor of presenting the deflection-hardening behavior, while the reinforcement diameter and UHPC cover thickness had little influence on the deflection-hardening behavior. The analytical models were established to predict the yielding load, peak load, and ultimate load of rebar-reinforced UHPC beams, and the predictions showed good agreement with the experimental results in this study. Also, the steel reinforcement could show a dominant role in the bearing capacity by increasing the reinforcement ratio. A post-yielding capacity factor lambda was proposed, which could reasonably evaluate the deflection-hardening and deflection-softening behavior of UHPC flexural members in the present study. Based on other experimental results collected in literature, three different ranges for the post-yielding capacity factor, namely, lambda <= 0.7, 0.7 < lambda < 0.9, and lambda >= 0.9, were identified, corresponding to the deflection-softening behavior, transition stage, and deflection-hardening behavior, respectively.

Automated summary

This paper experimentally investigates the flexural and ductile behaviors of ultra-high-performance concrete (UHPC) beams. The effects of reinforcement ratio, reinforcement diameter, and UHPC cover thickness on the behavior of the beams are studied. Increasing the reinforcement ratio significantly enhances stiffness, flexural capacity, and ductility, while the other two parameters have little influence. Analytical models are established to predict the behavior of the beams, and the predictions match well with the experimental results. The results of this study contribute to the understanding of the performance of UHPC beams and provide guidance for their design.