Torsional capacity of ultra-high-performance concrete beams using rectangle stirrup

This study studies the torsional capacity of rectangular ultra-high-performance-concrete (UHPC) beams. Nine UHPC beams were tested under pure torsion load. The failure modes were presented and the influences of parameters, including reinforcement ratio, stirrup ratio and steel fiber content were discussed. The experimental results showed that longitudinal reinforcement ratio had little effect on crack width and plastic stiffness in serviceability stage. Increasing the stirrup ratio and steel fiber content effectively inhibited the development of crack width and improved plastic stiffness. The torsional ductility of UHPC beams decreased with the increase of longitudinal reinforcement ratio but increased with the increase of stirrup ratio and steel fiber content. The cracking torque and elastic stiffness of UHPC beams were less affected by the reinforcement ratio and increased with the increase of steel fiber content. The twist, energy consumption, and ultimate torque of UHPC beams increased with the increase of longitudinal reinforcement ratio, stirrup ratio, and steel fiber content. The damage index of UHPC beams was 0.85-0.90, and the plastic stiffness accounts for 1/25-1/10 of the elastic stiffness.