TAKAGI Nobuaki Ritsumeikan University Faculty of Science and Engineering, Research Associate, 理工学部, 助手 (50154753)
NIWA Junichiro Nagoya University Faculty of Engineering, Associate Professor, 工学部, 助教授 (60164638)
SAEKI Noboru Hokkaido University Faculty of Engineering, Associate Professor, 工学部, 助教授 (80002004)
KOJIMA Takayuki Ritsumeikan University Faculty of Science and Engineering, Professor, 理工学部, 教授 (10066706)
In this study, the following results can be drawn.
1. Analytical studies on the mechanical behaviors of reinforced concrete beams subjected to torsion were carried out. The characteristics of the employed analytical method were to assume the original solid section of beam to be equivalent to a hollow one and convert the applied torsion into a uniform shear flow. Concerning the stress-strain relation of concrete, the softening, the tension stiffening and the shear transfer along cracks were considered. The effect of the local yielding of reinforcement was also incorporated into the analysis. It was admitted that the ultimate strength and general deformation behavior of reinforced concrete beams subjected to torsion could be predicted fairly well by the proposal analytical method.
2. Cover of concrete has a significant effect on the ultimate torque and deformation behaviors of concrete beams subjected to torsion, because the tensile resistance of cover concrete, the compressive resistance
of concrete strut and the depth of shear flow were largely affected by the depth of concrete cover. The space truss was not formed at the ultimate state in the concrete beams with large concrete cover, in which the number of cracks was small and the distribution of cracks was not so good. In such concrete beams, the calculated ultimate torque was overestimated.
3. The calculating method of the ultimate torque of reinforced concrete beams subjected to the combined load of torsion and flexure was proposed. This method underestimated the ultimate torque, when the reinforced concrete beams were subjected to large flexural load compared to torsion.
4. The ultimate torque increased with the amount of prestress even in the prestressed reinforced concrete beams with large section, where the shear flows (ql and qw) at the ultimate state were nearly the same and the steel ratios (pl and pw) of longitudinal steel and stirrup were also the same. The strain of prestressing bar at the ultimate torque was almost the same as that of prestressing bar tensioned at the prestressing, therefore the ultimate torque calculated by the JSCE method overestimated that of prestressed reinforced concrete beam, especially when the prestress was small. Less