Sep. 23, 1999 WEST LAFAYETTE, Ind. – A report published this month detailing damage from a June 15 earthquake in Mexico illustrates the need to enforce special seismic design standards for critical buildings such as schools, hospitals and fire stations.
The magnitude 6.5 quake was centered about 12 miles southwest of the city of Tehuaca, in the state of Puebla. It killed 17 people, damaged more than 1,000 schools, nine hospitals and more than 14,000 homes, displacing about 20,000 people. Some of the hospitals were forced to close just when they were most needed for surgeries and emergency services.
"Hospitals, fire stations and schools should meet higher standards specifically because of their special roles," says Julio Ramirez, a civil engineer from Purdue University who led a research team sent to the quake site by the Earthquake Engineering Research Institute (http://www.eeri.org), an international organization that aims to reduce the impacts of future earthquakes through research and public education.
A similar problem might exist within certain regions of the United States, such as the Midwest, where, because strong earthquakes are infrequent, the number of schools, other critical buildings and bridges with deficient seismic designs has increased over time, Ramirez says.
The issue is more urgent in Mexico than it is in the United States, in part because builders there construct roofs with heavier materials than the more expensive steel joists and girders preferred by American builders. Higher weight increases the forces exerted on buildings during earthquakes.
The buildings could often be strengthened with additional walls so that they better withstand earthquakes. In the case of one apartment building that collapsed, it is likely that just a few extra walls would have protected the building, Ramirez says.
The findings were detailed in a report prepared by Ramirez, Purdue graduate student Santiago Pujol and civil engineer James Miller from Degenkolb Engineers in San Francisco. More than 20 other researchers were involved in preparing the report, which appeared in the September issue of a monthly newsletter published by the earthquake research institute.
In addition to concerns about critical buildings, the report also concludes that design standards for low-income residential housing units need to be improved.
The researchers say in the report that "... a more effective public policy for earthquake hazard mitigation needs to be implemented in Mexico. In particular, the construction practices in urban centers do not offer sufficient protection in the case of individual housing units. Approximately 80 percent of these units are built without considerations regarding seismic resistance. It is further questionable that the avenues of reconstruction for the housing units offer sufficient assurances that seismic vulnerability will be reduced."
Meanwhile, the engineers also found evidence that damage from earthquakes accumulated over time, making certain types of old masonry buildings progressively more susceptible to collapse. More than 800 historic buildings in that region of Mexico were far more severely damaged in the June 15 quake than they were in previous, more powerful temblors.
The research was funded by the National Science Foundation.
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