Research on bending tests and modified calculation of flexural strength for hybrid reinforced pipe piles

To investigate the influence of ordinary reinforcement on the bending moment capacity of prestressed high-strength concrete (PHC) pipe piles, this study conducted flexural tests on four prestressed reinforced concrete (PRC) pipe piles with hybrid reinforcement and two PHC pipe piles. Through comparative analysis of their bending moment capacity, deformation characteristics, and crack propagation patterns, the enhancement mechanism of ordinary reinforcement on the bending moment capacity of PHC pipe piles was revealed. Based on the correspondence between the experimentally measured coefficient of relative compression zone area η and the theoretical value α, the existing calculation formula for the ultimate bending moment capacity of pipe piles was modified. The results indicate that increasing the rebar diameter enhances deformation resistance and alters the deflection development pattern. The use of ordinary reinforcement improves the bending moment capacity of PRC pipe piles by 36% to 51% compared to PHC pipe piles. In contrast to PHC pipe piles, PRC pipe piles exhibit a transition from sparse, wide cracks to dense, narrow cracks, demonstrating that ordinary reinforcement effectively restrains crack width propagation, thereby improving the ductility and service performance of pipe piles. The modified ultimate bending moment calculation formula for pipe piles significantly enhances computational accuracy and reduces dispersion while maintaining safety margins. These research findings provide a reliable theoretical basis for the optimized design and engineering application of PRC pipe piles.