Seismic retrofit and strengthening of buildings. Observations from the 2017 Puebla-Morelos earthquake in Mexico City

Abstract

Mexico City is frequently affected by the action of strong earthquakes which are primarily triggered from two seismic sources: a) subduction earthquakes along the Mexican Pacific Coast and, b) continental normal faulting earthquakes. As a consequence of strong earthquakes which have occurred since 1957, there are several hundreds of buildings in Mexico City which have been repaired or retrofitted after those strong earthquakes. Then, there is a valuable experience in the city on different seismic strengthening and retrofitting techniques for different structural systems. Rehabilitated buildings were again significantly tested during the Mw = 7.1 September 19, 2017 Puebla-Morelos continental normal faulting earthquake. In this paper, the authors focus their attention to the observed seismic performance of the most commonly used strengthening and retrofitting techniques within the city. From a detailed inventory of 1834 buildings compiled by the authors which experienced from light damage to collapse, 110 rehabilitated buildings experienced damage, but only 45 of them experienced severe structural damage or have been already demolished. It is worth noting that in only 18 rehabilitated buildings, the selected rehabilitation strategy was an important part of the observed severe damage. Unsatisfactory performances are discussed from different angles within the paper, highlighting the reasons for such bad performances. In many instances, bad performances were related to poor detailing, possessed structural irregularities, resonant responses, erroneous conceptualization for the strengthening/retrofitting scheme, partial retrofits, or lack of adequate maintenance. It was found that water penetration to foundation boxes or mats in soft soils favored progressive tilting. Very satisfactory performances are also highlighted. Iconic retrofitted buildings and building complexes are also discussed. It can be concluded that most strengthened and retrofitted buildings performed well in general, particularly when the strengthening/retrofitting 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.