Seismic Upgrading Strategies for Non-Ductile Plan-Wise Irregular R/C Structures

This study investigates the effectiveness of different strategies for the seismic retrofitting of a gravity-load-designed plan-wise irregular R/C building tested at the JRC Elsa Laboratory. An alternative retrofitting intervention based on both FRP wrapping and R/C jacketing applied to selected critical columns was proposed. The retrofitting strategy was focused on two main objectives: 1) relocating the centre of stiffness and strength in order to reduce the torsional component of the response of the structure; 2) increasing the local deformation capacity of columns and thus the global deformation capacity of the structure. Nonlinear dynamic time- history analyses and simplified procedures based on nonlinear static pushover analyses were carried out and comparison with the retrofitting interventions carried out at the JRC ELSA Laboratory were performed. Bidirectional damage indexes were used to identify the most critical columns affecting the seismic performance of the structure. The simplified procedure provided results consistent with the experimental evidence and allowed to easily select a suitable retrofitting strategy. Numerical results showed the effectiveness of the strength-and- stiffness relocation strategy based on R/C jacketing of selected columns, but the local ductility increase based on FRP wrapping of the other columns was necessary for significantly improving the global seismic performance of the structure in case of severe seismic excitation.