Factors influencing soft-story building failures during the September 19, 2017 earthquake in Mexico

The September 19, 2017 earthquake with epicenter in the Mexican Republic caused dozens of collapses of reinforced concrete buildings in Mexico City. A high percentage of these buildings on transition and soft soil sites, had a weak first story. In addition to the known seismic vulnerability of these buildings, other parameters as frequency content of the seismic records, seismic regulation, soil type, among others, influenced the collapse of the structures as well. Altogether, they explain better why the collapses occurred in some specific areas and in others, with similar intensities, did not generate the failure of the structures. Most of the buildings that partially or totally collapsed during the September 19, 2017 earthquake rested on soft soils. Additionally, many of them had a parking area supported by columns and beams on the first floor and apartments on the upper floors, supported by confined masonry walls, creating a weak ground-floor structure. This study evaluates the main parameters that influenced the observed collapses of buildings with weak ground floors during the September 19, 2017 earthquake. Nonlinear analyses of the buildings subjected to unscaled real accelerograms recorded during the earthquake were carried out. The results show that the following factors jointly contributed to the collapse of buildings: design criteria of the seismic regulation in force during the construction period of the buildings, the building height, the soil type on the building location, the frequency content of the seismic records and the soil-structure interaction.