Seismic response and reliability index of RC weak story buildings on soft soils of Mexico city

For more than 50 years, buildings with soft ground floors continue to suffer severe damage and collapse when subjected to seismic events. During the earthquakes of September 19, 1985 and 2017 that occurred in Mexico, a significant number of collapsed buildings had this type of structure. Currently, many existing buildings have a parking zone on the ground floor and apartments for residential use on the upper floors. The parking area is supported by columns and beams, whereas the slabs of the upper floors are supported by masonry walls, creating a weak story at the ground level. In order to explain the collapses of weak story buildings observed during the earthquake of September 19, 2017, this study evaluates the seismic response and determines the reliability indices of a typology of buildings with flexible ground floors in Mexico City. Additionally, passive control devices with friction energy dissipation, hysteric behavior and viscous dampers, were proposed to retrofit the buildings and increase the reliability indices of the structures. Results showed that the reliability indices of existing buildings with a weak ground floor are very low, which explains the observed damages and collapses during the 2017 earthquake. Reliability indices of the retrofitted buildings were significantly increased and the failure probabilities of the structures were strongly reduced, showing the effectiveness of passive control systems to mitigate the seismic risk of this type of structures.