Flexural and cracking behaviors of reinforced UHPC beams with various reinforcement ratios and fiber contents

This research is aimed at investigating the flexural and cracking behaviors of ultra-high-performance concrete (UHPC) beams. Nine UHPC beams with different reinforcement ratios (0, 1.0%, 2.9%, 4.8%, and 7.1%) and fiber volume fractions (2.0% and 3.0%) were considered under flexure. A section analysis was also performed to predict the flexural and cracking behaviors of UHPC beams and was verified by experimental results. The test results showed that the reinforcement and steel fibers can play a significant role in limiting crack development. Considering the performance of the steel fibers, a high-precision equation for predicting the average crack spacing of UHPC beams was developed. The formulas in the French standard NF P 18–710 overestimated the maximum crack width by a significant margin for the UHPC beams with a high reinforcement ratio (>4%). The flexural stiffness of the reinforced UHPC beams increased as the reinforcement ratio increased, whereas their initial stiffness without reinforcement was larger than that with a low reinforcement ratio of 1.0% because of the weak bond interface between the UHPC and the reinforcement. The flexural capacity of the UHPC beams basically increased linearly with the reinforcement ratios. The result of the sectional analysis indicated that the contribution of steel fibers to the flexural capacity decreased significantly with the increase in the reinforcement ratio. In the ultimate limit states design, the contribution of UHPC tensile capacity could be considered only as a safety reserve when the reinforcement ratio is greater than 4.0%, whereas its contribution needs to be considered for the UHPC beams with a reinforcement ratio of less than 2.9%.