PRESTRESSED HIGH-STRENGTH CONCRETE BEAMS UNDER TORSION

Fourteen prestressed high-strength concrete beams were tested to study their torsional behavior. The major variables were the concrete compressive strength, the aspect ratio of the beam cross section, the prestressing level, and the amount of torsional reinforcement. Keeping the area constant, three different cross-sectional dimensions, 240 x 240 mm, 170 x 340 mm, and 140 x 420 mm, were used to give aspect ratios of 1, 2, and 3, respectively. The concrete compressive strengths were 70 and 90 MPa (10,000 and 13,000 psi), and the beams were subjected to two levels of prestressing, corresponding to 0.05 f'(c) and 0.10 f'(c). Test results showed that the torque-twist relations for the tested beams were approximately linear up to cracking, and thereafter they were nonlinear. The aspect ratio and the concrete compressive strength influence both the torsional strength and the torsional stiffnesses at all stages of loading. Several theoretical methods available in the literature and developed for normal-strength concrete were used to predict the torsional behavior of the test beams. The space truss theory with softening of concrete gave the best prediction of the torsional strength of the test beams.