Behavior of FRP-reinforced UHPC tubular beams under torsion
Jun‐Jie Zeng, Xianwen Hu, Dehua Zhu, Zizhao Zhang, Hongchao Zhao, Yan Zhuge
Abstract
Novel structural elements made of fiber-reinforced polymer (FRP) grids and rebars reinforced ultra-high-performance concrete (UHPC) (referred to as FRP-UHPC tubular member) have been developed for marine construction. While FRP-UHPC tubular members have demonstrated excellent flexural and shear performance in previous studies, their torsional behavior remains underexplored. This paper presents an experimental investigation into the torsional performance of FRP-UHPC tubular beams. Four specimens were fabricated with varying numbers of FRP grid layers and sizes of FRP bars. Key torsional responses, including the failure patterns, torque-twist curves, and strain evolutions of different components, were analyzed. The results revealed that all specimens failed due to the rupture of the transverse FRP grid strips, while the longitudinal FRP grid strips and the longitudinal GFRP bars remained intact at the ultimate failure. Incorporating CFRP grids improved stress distribution, leading to the progressive formation of multiple smaller cracks, higher ultimate torque, and greater twist capacity. In addition, increasing the number of CFRP grid layers from one to two enhanced the effective utilization of the longitudinal FRP bars. In contrast, increasing the volume fraction of longitudinal GFRP bars from 2.68 % to 3.78 % improved the torsional deformation capacity but had minimal impact on the ultimate torque. These findings provide valuable data for future studies to develop computational models to predict the torsional behavior of FRP-UHPC tubular members.