Numerical simulation of shear-strengthened RC beams

► Nonlinear fibre beam model for RC beams including shear-bending interaction. ► Step-by-step time integration scheme to simulate changes in existent structures. ► Capture of strengthening effects accounting for previous damage of the structure. ► Good prediction of results of shear-strengthened beam tests available in literature. ► Numerical study of alternative strengthening solution with prestressed stirrups. A nonlinear and time-dependent fibre beam element model able to simulate the response of existing reinforced concrete (RC) frame structures subjected to repair and strengthening interventions is presented in this paper. The relevant attributes of the proposed formulation are: (i) its capability for considering shear effects in both service and ultimate levels and (ii) the step-by-step nonlinear sequential type of analysis, which allows capturing the strengthening effects, accounting for the state of the structure prior to the intervention. The 2D fibre beam element developed is based on the Timoshenko theory and a hybrid (kinematic/force) formulation is used to simulate the response of RC sections under combined normal and shear stresses. Biaxial constitutive equations assuming smeared rotating cracks are used to describe the behaviour of cracked concrete. The proposed model is validated with experimental results of a shear damaged and subsequently strengthened RC beam, available in the literature. An alternative shear strengthening solution with the use of prestressed stirrups is also presented. The importance of considering shear-bending interaction and previous damage in the numerical assessment of strengthened RC beams is highlighted.