Alternative seismic retrofit solutions for a non-ductile R/C structure

This study deals with the seismic assessment and retrofitting of existing under-designed R/C structures and the issue of selecting effective retrofit solutions is discussed. A displacement based procedure using nonlinear static pushover analyses is adopted in order to assess the main characteristics of the original structure and to select and compare the available retrofitting strategies. Different capacity curves can be estimated assuming different retrofitting solutions. The procedure is applied to a four-storey R/C frame tested at the JRC ELSA laboratory some years ago. The R/C frame was designed mainly for gravity loads without specific earthquake-resistant provisions. Accurate numerical models are developed to reproduce the seismic response of the R/C frame in both the original and retrofitted configurations. The effectiveness of three different retrofitting strategies is examined. First, a retrofitting intervention based on both FRP wrapping and R/C jacketing applied to selected critical columns is proposed with the main aim of improving the global ductility of the frame. Then, a retrofitting solution involving the introduction of eccentric steel bracings is investigated in order to reduce the displacement demand and to increase the energy dissipation capacity of the frame. The third intervention is carried out by adding a concrete shear wall to the short bay of the frame. This solution is efficient in controlling global lateral drift and thus reducing damage in structural members. Nonlinear dynamic analyses are performed to assess and compare the seismic response of the frame in the original and retrofitted configurations