Investigation on the Cause of Numerous Upper Floor Failures during the 1985 Mexico City Earthquake

摘要

The report includes the results of a study carried out to investigate the prevalent factors that contributed to the collapse of the upper floors of a large number of buildings during the earthquake of September 19, 1985, in Mexico City. The study involves the review of the collected data regarding such collapses, an examination of the apparent causes of the phenomenon, the design of a typical 10-story frame structure according to the 1976 Mexico City building code, and the nonlinear analysis of one of its frames under one of the ground acceleration records from the earthquake. It is found that in many cases the upper floor collapses might have occurred because the large accelerations and long duration of the earthquake induced in the failed buildings the formation of plastic hinges at the columns of some of their upper stories and because these plastic hinges in turn induced the lateral instability of such stories and the ones above them.