Review of Retrofit and Strengthening Strategies Used in Buildings in Mexico City After Strong Earthquakes

Abstract

Mexico City is often subjected to the action of strong earthquakes and then, thousands of severely damaged buildings in Mexico City have been repaired or retrofitted since the 1957 earthquake. Different integral techniques have been used, such as: a) column, beam and wall jacketing, b) addition of RC shear walls, c) addition of concentric steel bracing, d) post-tensioned exterior cable bracing, e) RC macro-frames, f) exterior exoskeletons, f) hysteretic energy dissipation devices and, g) reduction of stories (removal of top floors). These retrofitted and strengthened buildings techniques were again significantly tested during the Mw = 7.1 September 19, Puebla-Morelos continental normal faulting earthquake. In this paper, the observed seismic performance of the described strengthening and retrofit techniques of a representative inventory of buildings during the September 19, 2017 earthquake are reviewed. Both very good (most) and bad (fewer) performances are highlighted and discussed. It was observed and confirmed that, in general, most strengthened and retrofitted buildings performed well when the strengthening/retrofit strategy was integral, well executed, good maintained and the building was reasonably taken out of resonant responses or separated from their neighbors to reduce the potential of structural pounding. In addition, the dominant retrofit and strengthening techniques that are being used nowadays in Mexico City to rehabilitate buildings damaged as a consequence of the September 19, 2017 earthquake are also shown and discussed.