Mechanism of distributed composite GFRP bars in circular concrete members with and without spirals under shear

This paper presents experimental data and theoretical studies on the effect of distributed glass fiber-reinforced-polymer (GFRP) bars in circular concrete members. Th experimental program reports the test results of eight full-scale circular reinforced-concrete (RC) specimens with a total length of 3020 mm and a diameter of 508 mm were constructed and tested under shear load up to failure. The test specimens comprised three specimens reinforced with GFRP bars and spirals, three specimens with only longitudinal GFRP bars, and two reference specimens reinforced with conventional steel bars, with and without steel spirals. The various experimental parameters included the longitudinal reinforcement ratio, the type of reinforcement (GFRP versus steel), and presence of shear reinforcement. The shear strengths of GFRP circular concrete specimens, obtained from the experimental results, were compared to current codes and design guidelines as well as to the recently available shear design equations on circular concrete members in the literature. The test results indicate that the use of more GFRP bars distributed uniformly in the cross section, of the specimens with and without spirals, reduces the loss of flexural stiffness after cracking and increase the shear strength. The comparison indicates that some of the available design methods provide reasonable predictions.