Rotating compression field model for reinforced concrete beams under prevalent shear actions

The purpose of this paper is to improve the performance of a twodimensional finite element approach, called the Rotating Compression Field Model (RCFM). The RCFM capability for reproducing the non-linear behaviour of reinforced concrete (RC) beams, tested in shear with monotonic load increase, has been tested and amended. Concrete is treated as a quasi-orthotropic material with smeared cracks and smeared reinforcement. A modified version of the Sargin relationship for concrete in compression is adopted, introducing a new model for the softening branch of the stress-strain compression curve in the RCFM to take into account compression softening and the effect of confinement due to inplane reinforcement. In addition, this paper considers out-ofplane confinement effects using the model suggested by Eurocode 2. A key issue in the RCFM approach consists of relating the decay of effective concrete strength to the deviation angle between the inclination of the compression stress field at first cracking and its inclination at the load level considered. The validity of this relation has been extended from the original 15° up to more than 30°. A new stress-strain curve is implemented in the code to model the tensile behaviour of concrete without reinforcement (tension softening) in addition to the tension stiffening effect already present for concrete with reinforcement. This model leads to a successful comparison with experimental results on RC beams for a significant range of design parameters and mechanical material properties.