Maximum Torsional Reinforcement of Reinforced Concrete Beams Subjected to Pure Torsion

Structural design codes limit the maximum amount of torsional reinforcement of reinforced concrete (RC) members to prevent possible sudden torsional failure due to over-reinforcement. While the provisions in the ACI 318-19, EC2-04, CSA-14, and JSCE-07 codes are almost the same for torsional strength calculation of RC members based on the space truss model and thin-walled tube theory, different limits are used for the maximum amount of torsional reinforcement. The requirements of the maximum torsional reinforcement in the ACI 318-14 and JSCE-07 codes are based on the empirical equations, while those in the EC2-04 and CSA-14 codes are based on the truss model. To compare the accuracy of these four design codes, this paper presents the test results of 15 RC beams that have various torsional reinforcement ratios and concrete compressive strengths. The experimental and analytical results indicate that the ACI 318-14 and JSCE-07 design codes evaluate the torsional failure modes of 15 RC members with reasonable agreement, while the EC2-04 and CSA- 14 design codes overestimate the boundary between two torsional failure modes.