Effects of hysteretic energy demands on collapsed corner buildings during the September 19, 2017 earthquake in Mexico City

Abstract

Damage to buildings during earthquakes depends on the dynamic characteristics of the seismic event, soil properties, and the buildings’ attributes. Many buildings exhibit structural deficiencies from either the design conceptualization or the construction process. In Mexico and other seismically active countries such as Turkey, Japan, the United States, India, Chile, and Nepal, where highly destructive earthquakes have occurred, structural pathologies such as soft-story mechanisms and torsional effects have been identified as primary causes of building damage collapse. In particular, buildings on street corners are more vulnerable to torsional effects, mainly due to the asymmetric distribution of infill walls. Although many studies have investigated the seismic response of irregular structures and the effects of torsion on observed damage, very few have systematically analyzed the distribution of hysteretic energy demand in corner buildings and its correlation with seismic damage and building collapses. This study examines how the hysteretic energy demand is distributed among the structural elements of corner buildings with torsional pathology and its connection to the severe damage and collapses observed during the earthquake on September 19, 2017 in Mexico. Using post-earthquake data, numerical models were created to represent damaged and collapsed corner buildings primarily consisting of reinforced concrete frames with masonry infill walls. Nonlinear time-history analyses were conducted using recorded accelerograms from the site to assess the seismic response of the buildings in terms of interstory drift demand and hysteretic energy distribution, two key parameters directly related to structural damage. A comprehensive analysis of torsional effects on hysteretic energy distribution in columns, beams, and masonry walls was evaluated. The results highlight that although the amount of hysteretic energy dissipated by masonry walls is relatively small compared to the total energy dissipation, its asymmetric placement significantly alters the distribution of interstory drifts and increases localized demands on structural elements, particularly columns. Additionally, the study emphasizes the importance of analyzing corner buildings that accurately represent existing structures by incorporating the stiffness of masonry walls, rather than relocating the center of mass or center of stiffness. By integrating real post-earthquake building data and accelerograms recorded at seismic stations near the buildings, this study establishes a direct correlation between analytical results and observed structural damage, offering valuable insights into the mechanisms contributing to both partial and total collapses.