Torsional behavior of normal- and high-strength concrete beams

The experimental results of torsional strength and deformation for normal- and high-strength concrete (NSC and HSC, respectively) beams are presented. Eight NSC (f(c)' = 35 MPa) and eight HSC (fc' = 70 MPa) beams, with a cross section of 350 x 500 mm and various amounts of torsional reinforcement, were tested under pure torsion. Test results showed that the HSC beams had higher torsional strength and cracked stiffness than the NSC beams designed with the same amount of reinforcement. Beyond the peak strength, HSC beams exhibited relatively steeper strength decay than NSC beams for those with higher reinforcement. The experimental ultimate strength was approximately 1.1 times the calculated result by design provision of the ACI 318-02 Code. The orientation of compression diagonals was not affected by the compressive strength of concrete. For the same applied torque, the principal tensile strains in HSC beams were less than those in NSC beams.