Behaviour model and experimental study for the torsion of reinforced concrete members

The typical behavioural curve of a reinforced concrete element with longitudinal bars and stirrups under torsion comprises two distinct regions; the elastic part until the first cracking and the part after cracking. The different character of the response in these regions reveals the different nature of the load resisting mechanism in each case. The present work addresses an approach that combines two different analytical models in order to predict the entire torsional behaviour. The prediction of the elastic part until the first cracking is achieved using a smeared crack analysis for plain concrete in torsion, whereas for the description of the post-cracking response the softened truss model is used. Further, the results of an experimental investigation on the behaviour of 15 reinforced concrete beams subjected to pure torsion are also presented in this paper. The reported results include the behavioural curves and the values of the initial torsional stiffness, the cracking torque moment and the ultimate torque capacity of the beams. Analyses for the torsional behaviour of the tested beams using the proposed approach were performed and analytical curves are produced and compared with the experimental ones. A good agreement between predicted and experimental results is observed.