Torsional behavior of reinforced high-strength concrete deep beams

This paper presents the results of an investigation on the behavior of reinforced high-strength concrete (HSC) deep beams subjected to pure torsion. The test series consisted of 20 beams. The variables were the concrete compressive strength and span-depth ratio (L/h). Concrete compressive strengths of 54 and 94 MPa, and L/h of 1 to 5 were used. Constant transverse and longitudinal reinforcement ratios were used. Test results showed that the torsional strength and stiffness increase with the decrease of L/h ann the increase of concrete strength. The softened truss model theory is modified to account for the condition of deep beams. The theoretical model predicts the torsional strength and the deformations of elements throughout their postcracking loading history. The theoretical predictions using the modified model underestimated the torsional strength for beams with small L/h. Based on the test results, a semi-empirical expression for modeling deep beam action is proposed. The predictions are in good agreement with the test results.