Contribution of Closed Ties to Shear Strength of GFRP-Reinforced Precast Concrete Tunnel Lining Segments: Experimental and Analytical Study

Current tunnel design provisions do not consider the shear resistance of transverse reinforcement in precast concrete tunnel lining (PCTL) segments. Such reinforcement is often designed as a minimum for shrinkage and temperature resistance. This study evaluated the behavior and shear strength of PCTL segments reinforced with glass fiber‒reinforced polymer (GFRP) bars with and without closed shear ties. A total of five full-scale rhomboidal PCTL specimens with a 1,500 × 250 mm rectangular cross section and an arched length of 2,100 mm were constructed and tested under three-point loading up to failure. The testing parameters included the configuration of the transverse reinforcement (bars versus closed ties), the spacing of closed shear ties, the longitudinal reinforcement ratio, and concrete strength. The load–deflection behavior, cracking, failure mechanisms, shear capacities, and strain in the reinforcement and concrete are discussed herein. The results indicate that all specimens experienced shear failure because of the diagonal tension failure or shear compression mode. The presence of shear stirrups enhanced the structural performance of the GFRP-reinforced PCTL segments. In addition, increasing the closed-tie ratio, longitudinal reinforcement ratio, and concrete strength increased the shear strength of the segments. A comparison between the test results and predictions made with the critical shear crack theory (CSCT) was introduced in the theoretical approach to evaluate the applicability of existing FRP design code provisions. The predictions produced according to FRP design codes can be classified between conservative and nonconservative predictions. The modified CSCT yielded predictions closest to the experimental values with an accuracy of 98%.