WEST LAFAYETTE, Ind. – A structural engineer from Purdue University is proposing an unorthodox approach for simplifying the design of earthquake-resistant buildings in Turkey, which presently has a code that may be too sophisticated for practical use.
The "alternative engineering" method could enable Turkey to replace its complex building code, which is about 75 pages long, with a five-page version that would be more easily understood and applied by engineers.
"Turkey now has a building code, especially devoted to earthquake-resistant design, that is highly sophisticated and quite scientifically respectable," says Mete Sozen, an expert in the design of earthquake-resistant structures and the Kettelhut Distinguished Professor of Structural Engineering at Purdue.
The code, however, appears to be too good.
"It's very difficult for run-of-the-mill engineers to deal with calculations and methodologies that require virtually a Ph.D. to use," says Sozen, who was a member of a field-investigation team sent to the site of a devastating temblor that struck his native Turkey on Aug. 17.
He will present a paper about his proposal during a structural-engineering symposium Oct. 12 in Ankara.
"I call it alternative engineering because it goes against the norms of standard engineering," says Sozen, who has conducted research in about 25 quake-stricken regions during his career.
Usually, an earthquake-resistant building is designed by first defining its architecture: the weight and stiffness of construction materials is calculated, as is the structure's "period of vibration," or how it moves in response to ground motion from earthquakes. For example, the most rapid ground motions cause the smallest structures to sway more than skyscrapers. But tall buildings move much more in response to slow, soft ground motion, which leaves shorter structures less affected.
"In the alternative code that I'm proposing, we forget about all of these factors," Sozen says. "It is a very simple method for earthquake-resistant design of building structures."
The method revolves around the following, simple mathematical expression: one-half the sum of the cross-sectional areas of the building's columns, plus the sum of the areas of the horizontal cross sections of all the load-bearing walls, must be more than the total floor area divided by 1,000.
He originated the mathematical equation several years ago, working with a Purdue graduate and postdoctoral fellow, Ahmed Hassan, who is now an engineering professor at Cairo University. The equation was created as a tool to assess the earthquake-vulnerability of buildings, but Sozen recently realized that it might also be used to actually design earthquake-resistant buildings.
The alternative method does have its limitations, he says. It should not be used for buildings higher than seven stories. However, it could be applied to most buildings and would improve safety in the long run because the present code is so complex that it is difficult to put into practice.
Sozen was a member of a research team sent to the quake site by the Earthquake Engineering Research Institute, a national, non-profit association that aims to reduce future earthquake impacts through research and public education. He has written a preliminary report, which is available on-line.
"In earthquake engineering, we learn to expect the unexpected," he says. "Just about every time a new earthquake occurs, you get a surprise."
The biggest surprise about the Turkey quake was the unprecedented length of the time that the ground continued to shake. The shaking usually lasts about 30 seconds, but the series of successive shocks went on for five minutes during the Turkey earthquake, which was centered near the city of Izmit.
"I still can't believe it, but the records are there," Sozen says.
The 7.4-magnitude quake killed more than 15,600 people and left 600,000 people homeless. It caused $6.5 billion in damage, according to World Bank estimates. One particular town, Adapazari, was hit especially hard because its sandy, moist soil liquefied from the shaking.
"This was very much like boiling water," he says. "The ground kept bubbling with energy pumped in by successive bursts of fresh energy."
Some buildings literally listed into the ground like sinking ships, says Sozen, who is continuing his research at the Turkey site, focusing on the distribution and types of damage seen there.
"I'm still trying to straighten it all out in my mind," he says.
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