Damage modelling of reinforced concrete beams

Analysis of reinforced concrete building floor frames can be significantly improved when appropriate material models are assumed to represent the actual global behaviour and consequently to improve the ultimate and serviceability limit state verifications. Often, the stiffness reduction and the evaluation of the ultimate strain values are carried out by means of simple models based on bending moment-curvature diagrams and therefore the shear effects are neglected. In this work, an improved model to compute either the stiffness reductions or the ultimate loads has been proposed to take into account the non-linear effects due to the shear components. A damage model is adopted to govern the stress and strain fields across the cross-section of the reinforced concrete member. Then, a simple mechanism to transfer the shear stresses not sustained by the concrete material to the shear reinforcements. The shear reinforcement force resultant is computed according to the strain component measured in the tensile principal direction. The truss model for cracked concrete beams is adopted to compute the corresponding forces applied to the shear reinforcement. The well-known model, proposed by Mazars, has been implemented to govern the concrete behaviour based on the continuum damage mechanics, while an elasto-plastic model was assumed for the bending and shear reinforcements.