The influence of degradation phenomena on collapse modes in prestressed concrete beams

The static capacities of reinforced and prestressed concrete beams are characterised through their failure modes, which describe the internal force redistribution as well as the kinematic evolution which leads to the collapse of the structure. For a given structural element, a change in material and/or sectional characteristics due, for instance, to damaging effects induced by environmental aggressive agents, may change the element behaviour. In this paper, a computational approach, suitable to deal with the analysis of R.C. and P.C. concrete elements with steel bars and/or tendons subjected to corrosion is presented. The effects of the diffusion of aggressive agents, of the onset and of the development the corrosion state in the reinforcement and the corresponding mechanical response are studied. The damage development and the mechanical behaviours are dealt as coupled phenomena. A set of comparative applications shall demonstrate how in P.C. beams, the corrosion could switch a collapse of flexural type to one of shear type