Seismic assessment and retrofitting of a plan-wise irregular R/C structure designed for gravity loads

The seismic performance of an under-designed plan-wise irregular R/C structure tested at the Joint Research Centre – JRC (Ispra, Italy) and the effectiveness of a seismic retrofitting intervention based on both FRP wrapping and R/C jacketing applied to a number of critical columns are presented and discussed in this paper. The retrofitting strategy was selected on the basis of the structural deficiencies, that were highlighted by both numerical analysis and testing. Retrofitting was mostly aimed at reducing the torsional component of the seismic response and at improving the global ductility of the structure. Nonlinear dynamic time-history analyses were performed and bidirectional damage indexes were worked out to assess the seismic response of the structure in the original and retrofitted configurations. Simplified procedures based on nonlinear static pushover analyses taking into account the effect of torsion were used in the seismic assessment of the plan-wise irregular structure and in the selection of the retrofitting strategy. The simplified procedures adopted in this study (a) provided results, that were consistent with the experimental evidence and with nonlinear dynamic time-history analyses, and (b) allowed to identify the most critical columns affecting the seismic performance of the structure. The numerical results showed the effectiveness of the retrofitting strategy based on R/C jacketing of selected columns, with specific reference to the decrease of the torsional effects, but the enhancement of the column ductility provided by FRP wrapping was instrumental in improving the seismic behaviour of the under-designed structure, in case of high-level seismic excitation.