Local and Global Response Parameters in Seismic Risk Assessment of RC Frames Retrofitted by BRBs

This paper deals with the seismic performance and risk assessment of existing reinforced concrete (RC) buildings with limited ductility retrofitted by means of buckling restrained braces (BRBs). Two different approaches for evaluating the seismic vulnerability and risk before and after retrofit are introduced and analyzed. These approaches involve the use of different categories of engineering demand parameters (EDPs) for the system response assessment: global EDPs, that permit to obtain a synthetic description of the system behavior at a reduced computational cost, and local EDPs, more accurate in describing the response of the frame elements and of the BRBs, though more demanding from a computational point of view. The effect of the EDPs choice is analyzed by considering a two-dimensional RC frame designed for gravity-loads only as case study. The frame is retrofitted by introducing elasto-plastic dissipative braces designed for different levels of base shear capacity. The results of the study show that the use of global EDPs leads to a significant overestimation of the retrofit effectiveness in terms of both vulnerability and risk reduction. If a risk-based design is carried out for the retrofit system, braces with significantly lower dimensions are obtained by using global EDPs instead of local EDPs.