BRB retrofit of mid-rise soft-first-story RC moment-frame buildings with masonry infill in upper stories

Abstract

A high percentage of mid-rise soft-first-story (SFS) reinforced concrete (RC) buildings with masonry infill in upper stories collapsed in Mexico City during the SEPT/19/2017 earthquake. For this reason, in this work, an SFS building with similar structural characteristics to those damaged during such an event is subjected to several ground motions recorded at different Mexico City stations. As was expected, the peak drift demands are larger in comparison with the limit recommended by the Mexico City Building Code (2004). With an aim to improve the seismic performance of the building, three structural rehabilitation solutions are proposed and discussed. Then the seismic performance of the original building and the three rehabilitation solutions are compared via incremental dynamic analysis and structural fragility in terms of peak drifts. Among the three alternative solutions, it is shown that adding buckling restrained braces (BRBs) at the SFS of the building is a technique that leads to a structural fragility similar to that obtained when using a traditional rehabilitation technique; furthermore, when the BRB core area is reduced to an acceptable dimension, the forces transmitted to the foundation become lower, leading to an even better rehabilitation solution.