Seismic retrofit of pre-damaged RC elements using thin strain-hardening cementitious composite jackets

The emergence of cementitious materials with post-cracking strain hardening stress strain response in tension presents opportunities for retrofitting reinforced concrete elements through the application of very thin jackets, a technique that preserves the original geometry of the component. This retrofitting solution is studied experimentally in this work by replacing the damaged cover of lightly reinforced structural elements, which were previously tested under cyclic displacement reversals, simulating earthquake effects. Test specimens were detailed to represent older construction practices, where inadequate lap splicing of longitudinal reinforcement, light transverse reinforcement and thin concrete covers were common. Upon cyclic loading of the retrofitted components, the contribution of the thin jackets to the strength and deformation recovery of the old type reinforced concrete elements was examined considering the pre-existing damage. It was found that the efficacy of cover replacement with strain-hardening composites is significant not only for strength recovery but also in terms of enhanced deformability of the retrofitted component. The experimental response envelope was simulated using advanced nonlinear finite element modeling to gain improved insights regarding the stress state in the cover-replacement retrofitting layer, and to explore the performance of this retrofitting method for parameter values beyond the range of the experimental program. The amount of confinement exerted by the strain hardening cover was related to the tensile strength of the cover material and it controlled the strength recovery. However, by suppressing all brittle modes of failure along the shear span of the component, the reinforcement anchorage in the footing dominated the eventual failure mode.