The Mexico Earthquake of September 19, 1985—The Seismic Performance of Buildings with Weak First Storey

Abstract

During the Michoacan earthquake of Séptember 19, 1985, 8 percent of the damaged buildings in the Mexico City area were characterized by a first storey much weaker than the upper ones. Although it is recognized that these failures may have resulted from the combination of several features, in this paper it is intended to study the possible influence of the lateral strength discontinuity in the ductility demand at the first storey, and to try to understand the behaviour of this type of structures under the actions of the East-West component of the highest acceleration record obtained on soft soil in Mexico City during the mentioned earthquake. A parametric study for five and twelve-storey buildings with weak first storey is presented in this paper. The infill walls in the upper storeys were brittle in some cases and ductile in others. For certain cases, the results show the existence of a range of values of the ratio of seismic lateral resistance of the upper storeys to that of the lowest one for which ductility demands at the lowest story can be considerably higher than for other intervals. It is shown that the absorption capacity of ductile walls plays an important role in the displacement ductility demands of the first storey.