The collapse of Álvaro Obregón 286 building in Mexico City during the September 19, 2017 earthquake. A case study

Abstract

During the September 19, 2017 Puebla-Morelos Earthquake in Mexico City, 46 buildings experienced global or partial collapses. However, perhaps the most emblematic collapsed building during this earthquake was Álvaro Obregón 286 building (AO-286), located at Hipódromo Condesa District in the soft soils of former western Lake Texcoco. Unfortunately, 49 people died there, being the building which claimed more victims in Mexico City during this earthquake. Taking aside this tragedy, the collapse of Alvaro Obregón 286 building is an interesting case study from a structural engineering viewpoint, as it has several angles to explore to try to explain the reasons of its failure. In this paper, the authors report a detailed study that they conducted to try to understand better the collapse of AO-286 building and the observed damage in the neighboring AO-284 building. As no blueprints or lab data were publicly available, the authors did first a forensic study. Information was gathered from sources like press reports, public information and pictures taken at the site by the authors and by many other people. Then, using Google Maps and Google Earth information and tools, the following items were defined and measured: plan geometries and dimensions, story heights, locations of main structural axes, likely cross sections of structural resisting elements and observed tilting. With all this information, the authors estimated the likely steel reinforcement in reinforced concrete members and steel sections that these buildings could have had by designing them according to the recommendations available in the 1957 building code which was used in their design, using also the analytical methods and design practices at the times. Observed tilting before the earthquake, soil-structure interaction effects and the likeliness of structural pounding between AO-286 and AO-284 buildings were considered within the study. The recorded ground motions at nearby CI05 station were used for nonlinear dynamic simulations. From all these studies, it can be concluded that although AO-286 building did not have enough strength and ductility to survive the severity of the ground motions (when studied alone), structural pounding with AO-284 building, favored by the existing tilting in both buildings due to progressive soil settlements and soil-structure interaction effects had an important role in the observed collapse for AO-286 building and the severe damage observed in AO-284 building.