Required building separations and observed seismic pounding on the soft soils of Mexico City

Abstract

In this paper, the authors discuss the extensive structural pounding observed in Mexico City during the September 19, 2017 earthquake. A critical review of the recommendations available for required separations between adjacent buildings in the seismic codes of Mexico City since 1966 is offered. The reasons why these recommendations have not been effectively enforced since then are also addressed. A parametric study was conducted to understand better the structural pounding phenomena for strong ground motions which have been recorded in soft soils in Mexico City during the 1985 and 2017 earthquakes. For this purpose, equivalent frame models for existing reinforced concrete and structural steel flatslab buildings with nonlinear pounding contacts were used. Some well-known proposed equations for building separations were evaluated based upon the results of these parametric studies for pounding. The evaluated equations were the ABS, SRSS and DDC rules, as well as the absolute difference combination (ADC) rule proposed by the authors. From the obtained results, it was found that the minimum building separation between adjacent buildings established in the seismic code of Mexico City should be raised to avoid strong pounding on soft soils. Also, it was found that both the DDC and ADC rules are promising in defining building separations closer to the one obtained from dynamic simulations. These equations are less conservative than the version of the absolute sum rule currently established in Mexican seismic codes.