Sismica

Ongoing research on seismic performance of existing and rehabilitated school buildings in mexico

ABSTRACT
Outstanding results of an ongoing research program on the performance of existing and rehabilitated school buildings in Mexico are summarized. Analytical studies have confirmed the vulnerability of prototype RC buildings to a sidesway mechanism in the longitudinal direction when infillsare separated from the frame structure. In cases analyzed, structure strength was smaller than code required strength. In the experimental phase, adequate behavior under service-level earthquakes was confirmed for the bare frame specimen. In the test series aimed at reproducing the typical short column failure mode observed in earthquake reconnaissance, strength of masonry infill was found to becritical to preclude a column failure.

1. INTRODUCTION
Design philosophy of school buildings in Mexico, similarly to other countries, establishes that these facilities must remain operational after an urban emergency, such as the occurrence of an earthquake. In Mexico, besides hosting students for regular learning activities, school buildings are typically used as shelters. Therefore, specialattention has given to this type of buildings by considering an importance factor of 1.5 which is applied to the demand-side of the design equation. However, the 1985 Mexico City earthquakes, as well as the M7.1 Tehuacán, Puebla, the M7.3 Oaxaca and the M7.8 Tecomán, Colima (EERI-SMIS, 2006) earthquakes, have shown that some school buildings exhibit medium-to-high vulnerability rates. Economiclosses in this sector range between 10 and 20% of the total losses as shown in Fig. 1.

Typical damage patterns in school buildings comprise nonstructural components and short column failures (Fig. 2). Cause of damage is credited to deficient construction procedures, typically because nonstructural wall parapets are not separated from the lateral-load structural system, as well as to lack of properdetailing to resist earthquake-induced forces because buildings had been designed following obsolete construction codes.

a) 1985 Mexico earthquakes b) 1999 Tehuacán and Oaxaca earthquakes
Figure 1: Economic losses due to earthquakes in Mexico

a) Short column damage b) Facade damage
Figure 2: Typical seismic damage in school buildings

In the aftermath of the1985 earthquakes, a series of analytical and experimental research programs were undertaken aimed at understanding the causes of damage, as well as at analyzing the suitability of rehabilitation techniques. A large, comprehensive program was developed to rehabilitate schools that were either damaged or that exhibited similar characteristics to those damaged; this was the case in Mexico City.Unfortunately, over the years the importance of this program decreased and a large number of buildings were left unattended, typically in states along the Mexican Pacific coast.

Recently, efforts have been retaken aiming at investigating failures of school infrastructure and at proposing recommendations to reduce its vulnerability. In this analysis, it was apparent that most school buildings followprototypes built with reinforced concrete or steel structures. According to the Mexican agency that was up to a few years in charge of building schools, CAPFCE, there are about 60 prototypes and more than 200,000 school buildings in the country. However, an assessment of their vulnerability and structural safety is lacking.

Current efforts are concentrated in the study of prototypes used in thezones of highest seismic hazard in Mexico. According to CAPFCE, most widely used prototypes are one- and two-story reinforced concrete structures.

In this paper, outstanding results of the analytical and experimental phases of a research program are summarized. A two-story reinforced concrete structure was used as a model structure for this initial phase. Tests on existing structures and on...