Minimum torsional reinforcement ratio for reinforced concrete members with steel fibers

The current design codes for concrete structures suggest the minimum torsional reinforcement ratio to induce minimum ductile failure after cracking in reinforced concrete (RC) members subjected to torsional moment. However, as the member strengths are quite often lower than the torsional cracking moment strengths even when satisfying minimum torsional reinforcement ratio specified in the current codes, it may not serve the original purpose of preventing brittle failure immediately after cracking. In this study, a rational equation is thus presented for calculating the minimum torsional reinforcement ratio that could provide a sufficient margin of safety in design. The minimum fiber factor to be applied in steel fiber reinforced concrete (SFRC) members is also proposed. The proposed model was found to reflect the effects of torsional cracking strength, longitudinal and transverse reinforcement ratio, and the presence of torsional reinforcement in concrete members. It was also found that as the reserved strength included in the proposed equation is determined based on the test results of the RC members, it contains an appropriate factor of safety for the RC members. In addition, it was confirmed that the minimum fiber factor is conservative compared with the collected test results of the SFRC specimens.