Do Directionality Effects Influence Expected Damage? A Case Study of the 2017 Central Mexico Earthquake

Abstract

We analyze the case of a building that collapsed in a multifamily complex of Tlalpan borough in Mexico City during the 19 September 2017 Central Mexico earthquake. Despite having similar materials and similar structural and geometric properties, this was the only building that collapsed in the complex. A structural analysis of the building and a study of the soils' predominant periods indicated that resonance effects, if any, would not be significant. However, phenomena related to the anomalous performance of buildings in dense urban areas, such as geological soil, soil-structure interaction, and soil-city interaction effects were also investigated. A detailed analysis of the directionality of seismic actions recorded at nearby accelerometric stations and of the azimuths of sound and damaged buildings pointed to directionality effects as responsible for the collapse of the building. Subsequently, a set of fifty-eight, two-component acceleration records of the earthquake in the city was used to perform a thorough directionality analysis. The results were then compared with the foreseen uniform hazard response spectra and the design spectra in the city. Seismic actions in the city due to this earthquake were stronger than those corresponding to the uniform hazard response spectra. In addition, although design spectra have been significantly improved in the new 2017 Mexican seismic regulations, they were exceeded in eleven of the fifty-eight analyzed spectra. In four of these eleven cases, the design spectra were exceeded due to directionality effects. These results confirm the necessity of considering directionality effects in damage assessments, in strong motion prediction equations, and in design regulations. * Definitions apply for peak ground acceleration (PGA) and for response spectral accelerations, Sa (T), which are functions of the period, T, of vibration.

An Efficient Method for Considering the Directionality Effect of Earthquakes on Structures

“…It has been demonstrated that the structural response strongly varies depending on the orientation of the structure with respect to the seismic action. For instance, Vargas-Alzate et al [2018] and Pinzón et al [2018a] demonstrated how buildings with very similar structural system and dimensions, located very close to each other, had different damage states depending on their orientation respect to the earthquake source.…”

“…Notice that, the predominant acceleration acting on a structure will also depend on its azimuthal orientation. This effect has been widely studied focusing on the expected performance and damage in structures and on the seismic hazard [Lagaros, 2010;Mackie et al, 2011;Nguyen and Kim, 2013;Torbol and Shinozuka, 2014;Bradley and Baker, 2015;Fontara et al, 2015;Vargas-Alzate et al, 2018;Pinzón et al, 2018a].…”

Seismic Site Classification from the Horizontal-to-Vertical Response Spectral Ratios: Use of the Spanish Strong-Motion Database

“…RotD100 is the spectrum that represents the maximum (100th percentile) values of response spectra of the two as-recorded horizontal components rotated onto all non-redundant azimuths [13]. This is due to the directionality effect of strong motion recordings, which is now considered in the GMPEs [12,14,15] and in the variability of the performance of structures due to the angle of incidence of the seismic action [16][17][18][19].…”

Assessment of Post-Earthquake Damaged Building with Interferometric Real Aperture Radar

“…Buildings in the San Fernando neighborhood suffered various damage grades. Significant differences among damaged nearby buildings have been attributed to directionality effects of the strong ground motions [2,3].…”