This paper presents a tool for non-linear analysis of concrete and RC structures that aims to be suitable for performance based design. A three-dimensional isotropic plastic-damage constitutive law developed by the authors is used to simulate concrete behaviour. This law has two distinct damage parameters that detect the progression of damage in reinforced concrete panels and shear walls and therefore can help in interpreting their inelastic response. A RC membrane element for two-dimensional problems and a RC plate element for three-dimensional ones were developed. The reinforcing bars are simulated with a smeared approach: multiple smeared layers with uniaxial stress-strain response are used to profitably represent set of bars with different area and orientation; in this way it is possible to simulate most common reinforcing details. Particular attention is focused to the implementation of these models into the object oriented framework OpenSEES and to the post-processing utility developed in MATLaB and GiD. In fact they allow an excellent visualization of the damage indexes computed at the local level by the material constitutive model. It will be shown that such damage contours are powerful tools for interpreting the behaviour of the structure, its accumulated damage and its failure mechanisms Several showcases on deep beams, slabs and three-dimensional reinforced concrete shear walls show both the ability of the model to represent the experimental evidence for performance assessment and its potentiality for the performance based design of concrete and RC structures.