Reinforced Concrete Beams with and without FRP Web Reinforcement under Pure Torsion

Because of a lack of research on torsion, the Canadian design codes and AASHTO design specifications do not provide torsion provisions for the design of concrete bridge members reinforced with fiber-reinforced polymer (FRP) bars and stirrups. This paper reports on eight full-scale RC beams tested under pure torsional loading. The beams measured 4,000 mm long, 250 mm wide, and 600 mm deep. The test variables were the type and ratio of torsional reinforcement. Sand-coated glass-FRP (GFRP) and carbon-FRP (CFRP) bars and stirrups were used. The test beams included three beams totally reinforced with GFRP, three beams totally reinforced with CFRP, and two control beams reinforced with conventional steel. One beam for each of the three types was built without stirrups to determine the concrete contribution to torsional resistance. The test results indicate that all specimens failed as a result of diagonal torsional cracking. The test results were analyzed and compared with the corresponding predicted values using the new design provisions in recent standards. In addition, the cracking torsional strengths were compared to the available design equations in the literature (elastic theory, skew-bending theory, codes, and standards). The results of this study can be used as a fundamental step toward code provisions for using GFRP or CFRP stirrups as transverse torsional reinforcement in RC bridge and parking-garage applications.