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

研究了预应力钢筋混凝土梁在纯扭转作用下的极限扭矩，重点研究了极限状态下纵筋和箍筋的剪切流动(Q_1和Q_w)、配筋率(P_1和P_w)、预应力以及扭转截面的有效面积。可以得出以下结果：1.即使是大截面预应力钢筋混凝土梁，极限扭矩也随着预应力量的增加而增大，极限状态下的剪力流(q1和qw基本相同)，纵筋和箍筋的配筋率(p1和pw)也相同。极限扭矩下的预应力筋的应变与张拉的预应力筋的应变基本相同。虽然预应力筋在反复荷载作用下的应变在极限扭矩后有所增加，但扭矩、扭矩并没有增加。因此，假设预应力在极限状态下消失，JSCE法计算的极限扭矩高估了预应力钢筋混凝土梁的极限扭矩，特别是当预应力较小时。从1和2的计算结果来看，在计算预应力钢筋混凝土梁的极限扭矩时应考虑预应力的影响。在极限扭矩下，高强箍筋的应变很小。高强箍筋不能有效抵抗扭转。扭转有效面积对极限扭矩有显著影响，特别是在梁的截面较小时。

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.