Simple test identifies earthquake-vulnerable buildings
[SANTIAGO] A cheap, simple method that ranks buildings according to their vulnerability to earthquakes could be used in developing countries to reduce the impact of future catastrophes, according to researchers.
Scientists from Haiti and the United States tested the method retroactively in Haiti following the magnitude 7 earthquake in January. Their research has been submitted to a special Haiti issue of Earthquake Spectra.
The system was first developed in 1968 in Japan and later tested in Chile after the 1985 earthquake, in Anguilla as part of the Caribbean Disaster Mitigation Project in 1998, and in 2000 in Bogotá, Colombia.
Buildings are indexed using a numerical method that compares the combined cross-sectional areas of all the ground-storey columns and walls with a building's total usable floor area. The advantage of the method is its simplicity.
"This method [is] useful for countries with limited resources to train a group of engineers to rapidly assess buildings in areas where future earthquakes may occur, in order to avoid major catastrophes," Patrick O'Brien, a researcher at Purdue University, United States, and lead author of the study, told SciDev.Net.
"Although it may not be as precise as more detailed analyses, we found a correlation between the measured priority index [index of vulnerability] and the level of damage caused by the earthquake," O'Brien added.
Approximately 40 per cent of the 170 buildings surveyed in Haiti had been severely damaged by the earthquake. If the index had been used prior to the quake, 90 per cent of those buildings would have been classified as vulnerable, say the researchers.
But O'Brien admitted that the method is not completely accurate, as it does not take into account other factors such as soil and site conditions, ground motion intensity, building design, building materials and construction quality.
Ricardo Lopez, professor of structural engineering at the University of Puerto Rico, told SciDev.Net that this method is the best one available for visually estimating the expected damage from earthquakes.
"It is not an exact method nor it pretends to be," he said. "If a more detailed evaluation is required, then better information about the construction details and about the ground motion characteristics is required. But for general evaluation of expected damage in an area, no method is better."