Flexural behavior of rectangular hollow UHPC beams using glazed hollow beads

This work experimentally and numerically studied the bending behaviors of rectangular hollow UHPC (RH-UHPC) beams using glazed hollow beads. Four-point flexural tests were performed on eight RH-UHPC beams with varying glazed hollow bead contents, hollow ratios and longitudinal reinforcement ratios. The experimental results, including the failure mode, load-deflection response, load versus maximum crack width curve, and longitudinal strains of concrete in the mid-span section were obtained and analyzed. Results found all RH-UHPC beams displayed a bending failure mode, which was characterized by a flexural crack occurring in the pure bending zone and numerous micro-cracks. The increase of longitudinal reinforcement ratios and the incorporation of glazed hollow beads could effectively inhibit concrete cracking propagation. The effect of the hollow ratios on crack progression was more significant in specimens with the hollow ratios rising from 0.22 to 0.28. When the hollow ratios varied from 0.17 to 0.28, the cracking load, peak load and flexural stiffness of beams reduced by 19.4 %, 30.2 % and 11.9 %, respectively. As the replacement ratio of glazed hollow beads reached 10 %, the optimal flexural performance of beams was achieved. Additionally, the finite element (FE) models were established and benchmarked using tested results. Subsequently, a parameter analysis was carried out to investigate the effects of hollow ratio, longitudinal reinforcement ratio, and material strength on the flexural capacities of beams. Finally, the applicability of the current design approach for predicting the ultimate bending moment of RH-UHPCs was evaluated and the modified formulas for calculating the flexural capacities of this type of members was suggested.