Study on the Design Method of Prestressed Reinforced Concrete Beams Subjected to Torsion

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The ultimate torque of prestressed reinfored concrete beams subjected to pure torsion was investigated especially by focussing on the shear flows (q_1 and q_w) of longitudinal steel and stirrup at the ultimate state, steel ratios (p_1 and p_w), prestress, and the effective area of cross section for torsion. The following results can be drawn.1. The ultimate torque increased with the amount of prestress even in the prestressed reinforced concrete beams with large section, where the shear flows at the ultimate state (q_1 and q_w were nearly same, and the steel ratio (p_1 and p_w of longitudinal steel and stirrup were also same.2. The strain of prestressing bar at the ultimate torque was almost same as that of prestressing bar tensioned at the prestressing. Although the strain of prestressing bar increased under the repeated load after the ultimate torque, torque, torque did not increase. The ultimate torque calculated by JSCE method assuming that prestress disappears at the ultimate state, therefore, overestimated that of the prestressed reinforced concrete beam, especially when the prestress was small.3. From the results of 1 and 2, prestress should be taken into account in calculating the ultimate torque of prestressed reinforced concrete beams.4. The strain of high-strength stirrup was very small at the ultimate torque. High-strength stirrup does not resist the torsion effectively.5. The effective area for torsion remarkably influences on the ultimate torque, especially when the cross section of beam was relatively small.