Effect of Tension Stiffening on Torsional Behaviour of RC Square Columns

Considering the brittle nature of torsional failure of reinforced concrete (RC) members and high safety requirement for important structures like bridges, it is essential to accurately predict the torsional behaviour of such members for the purpose of efficient design of these members. However, very few analytical models are available in this field to predict the response of RC members under torsional load condition. Softened truss model (STM) developed in the University of Houston is one of them, which is widely used for this purpose. However, in the present study, it is found that STM prediction is not sufficiently accurate when compared to test results, particularly in the post cracking region. The present study aims at developing an improved analytical model for RC square members under torsional load conditions. Since concrete is weak in tension, its contribution to torsional capacity of RC members was neglected in the original STM. The present investigation revealed that, disregard to tensile strength of concrete is the main reason behind the discrepancies in the STM predictions. The original STM has been extended in this study to include the effect of tension stiffening (TS) to get an improved prediction of torsional behaviour of RC members. Three different tension stiffening models have been considered in this paper. The efficiencies of the models were calibrated through comparison with test data on local and global behaviours. Findings of this paper can be useful for further parametric studies on this topic