Torsional Performance of HSC Box Girders Reinforced with GFRP Bars

The behavior of high-strength concrete (HSC) box girders reinforced with glass-fiber-reinforced polymers (GFRP) under pure torsional loading has not been addressed, so far. Three large-scale concrete box girders reinforced with GFRP bars and stirrups were cast and examined under pure torsional loading over a clear span of 2000 mm. The box girders measured 4000 mm long, 380 mm wide, 380 mm deep, and 100-mm wall thickness. The test parameters include the web reinforcement configuration (spirals vs. ties) and concrete strength (NSC vs. HSC). The test specimens included two girders constructed with NSC—one reinforced with GFRP continuous spirals and one with GFRP individual ties—and the last one with HSC and GFRP continuous spirals. The test results indicated that the specimen with HSC and spiral stirrups exhibited the highest pre-and-post-cracking torsional strength and stiffness compared to counterpart specimens with NSC and ties or spirals.