Torsional Strength of Reinforced Concrete Members Failing by Crushing

The torsional strength of reinforced concrete members that fail by yielding of the reinforcement can be accurately predicted by design codes such as ACI 318-19 and the Canadian design standard CSA A23.3:19. However, these codes are relatively poor at predicting the strength of heavily reinforced members that fail by crushing. This paper presents a rational model which can predict the strength of such members. A key feature of the model is that the variation in torsional stresses through the thickness of a member is explic-itly considered using stress block factors derived from the stress -strain curve of the concrete. The model predicts the strength of 31 experiments with an average test-to-predicted ratio of 1.20 and a coefficient of variation (COV) of 14.4%. This is significantly better than the maximum torsion limits in ACI 318-19 (mean 1.62, COV 21.0%) and CSA A23.3:19 (mean 0.79, COV 41.1%). Simple equa-tions suitable for design are presented.

Automated summary

This paper presents a rational model for predicting the strength of heavily reinforced concrete members that fail by crushing, which is more accurate than design codes such as ACI 318-19 and CSA A23.3:19. The model takes into account the variation in torsional stresses through the thickness of a member using stress block factors derived from the stress-strain curve of the concrete. The predictions of the model have a higher accuracy compared to the maximum torsion limits in existing design codes, with an average test-to-predicted ratio of 1.20 and a coefficient of variation of 14.4%.