Some Retrofit Options for the Seismic Upgrading of Old Low-Rise School Buildings in Mexico

Abstract

An analytical study regarding the seismic upgrading of typical 60's and 70's designs for public school buildings in Mexico is presented. Some schools with these designs were moderately damaged during the 1985 Michoacán Earthquake in Mexico City. The damage was primarily observed in their longitudinal direction where existing slender RC columns have their weak axis. In addition, these columns are confined and shortened by masonry walls that do not run all the story height. These walls are supposed to be non-structural components, however, they experienced shear cracking during the quake due to the distress of the confined columns. Some school buildings were retrofitted after the Michoacán Earthquake adding post-tensioned bracing systems composed of prestressed high-slenderness steel strands (tension-only bracing systems), a retrofit option that is economical. In fact, there is an interest on assessing the effectiveness of this retrofit scheme in other regions with different soil conditions, as for example, the hard soils of the Mexican Pacific Coast. Therefore, the post-tensioning retrofit scheme used for the school buildings in Mexico City was also evaluated for hypothetical locations in the Mexican Pacific Coast. Another option that seems economical for the seismic retrofit of old school buildings in the Mexican Pacific Coast is the use of base isolators. Then, a retrofit plan using lead-rubber bearings was also evaluated. Acceleration time-histories recorded in the Mexican Pacific Coast during the 1985 Michoacán and the 1995 Manzanillo Earthquakes were used to assess the effectiveness of the studied retrofit schemes. Records in Mexico City for the 1985 Michoacán Earthquake and postulated ground motions for a Ms = 8.1 earthquake in Mexico City were also used. The effectiveness of each retrofit scheme is discussed through the comparison of the seismic behavior of original and retrofit structures using a comprehensive set of analyses.