Experimental investigation on torsional behaviors of ultra-high-performance fiber-reinforced concrete hollow beams

Limited studies have been conducted on the torsional performance of ultra-high-performance fiber-reinforced concrete (UHPFRC) hollow beams. This paper presents experimental investigations on eight UHPFRC hollow beams with various cross-sectional dimensions, wall thicknesses, and cross-section types. Their torsional responses, including the failure modes, torque−twist curves, torque−strain curves, torsional stiffness, and ductility indexes, are presented. Theoretical methods were employed to evaluate the cracking and ultimate torques. The results indicated that the UHPFRC hollow beams with and without flange plates exhibited a similar failure model, with the main cracks penetrating spirally. The cross-sectional dimensions, wall thicknesses, and cross-section types significantly affected the ultimate torque, whereas the cracking torque was affected only by the cross-sectional dimensions. A comparison of the experimental and theoretical results indicated that the American Concrete Institute code provisions provided good predictions for the cracking torque, whereas the existing theoretical methods offered unsatisfactory predictions for the ultimate torque. Thus, the equivalent wall thickness of UHPFRC hollow beams must be evaluated with a higher accuracy.