An enhanced finite element model for reinforced concrete members under torsion with consistent material parameters

International audienceThis paper deals with the development of a non-linear finite element model for reinforced concrete members under torsion. Using multi-fiber approach and displacement-based formulation, an enhanced multi-fiber 3D beam is proposed for predicting the behavior of reinforced concrete elements under torsion. The sectional analysis under elastic torsion is considered following Saint-Venant torsional theory for beam in order to take into account the effect of warping phenomenon. Elastic behavior under large displacements is also investigated in this model using a second-order approximation of the Green-Lagrange strains. In the inelastic domain, after cracking, following the space truss theory, the whole element is assumed to act as a tube, meaning the applied torsional moment is resisted only by the shear flow in the wall of the tube. Then, the effective wall thickness of the member after cracking is determined by an empirical formulation developed by the authors. Moreover, the section is discretized into different regions following its material response. In each region, depending on its characteristics, an appropriate constitutive material model is applied. For the concrete, the proposed behavior models are based on the Modified of Compression Field Theory and its extension. In order to correctly predict the torsional response, the authors proposed some modifications in the tensile behavior of concrete, based on experimental tests in torsion. In the elastic domain, the model is validated by comparing to the analytical solution and some results from other researches. In the inelastic field, a good agreement is obtained between a series of experimental tests and numerical results