Seismic performance of concrete structures exposed to corrosion: case studies of low-rise precast buildings

The structural members of precast one-storey or low-rise multi-storey concrete frames for industrial or commercial buildings are often directly exposed to the environment without any protection. The aim of this paper is to investigate the seismic performance of this type of structure considering the material degradation induced by the diffusive attack of aggressive agents, like sulphate and chloride, that may lead to deterioration of concrete and corrosion of reinforcement. The time-variant structural performance of the critical cross-sections of the columns, where plastic hinges are expected to occur during a seismic event, is investigated in terms of bending moment versus curvature relationships. Push-over and push-pull cyclic analyses are then carried out over the structural lifetime to assess the global structural performance in terms of base shear forces and displacement ductility. In this way, even though the lifetime evolution of the dynamic behaviour under ground motion is not captured, it can be shown how the hierarchy of member strengths, and hence the energy-dissipating failure mode claimed for a capacity design of the structure, can be affected by the time-evolution of damage. The proposed procedure is applied to investigate the lifetime seismic performance of one-storey and three-storey frame structures. The results show a significant reduction of both base shear strength and displacement ductility over the structural lifetime and highlight the importance of a lifetime approach to seismic assessment and design of concrete structures.