THE earthquake that turned many of Kobe鈥檚 buildings to rubble last week should not topple Japan鈥檚 building codes, which are stricter even than California鈥檚, say American earthquake engineers. Many of the buildings that collapsed probably followed an outmoded Japanese design strategy from the 1950s and 196Os.
Engineers design modern office buildings, bridges and over-passes with preplanned weak spots. During a severe earthquake, these weak spots break or buckle, absorbing some of the energy of the shaking and reducing the chance that the whole structure will collapse. The drawback to such a design is that the building may give way at the weak spots during less violent quakes, and require extensive 鈥� and expensive 鈥� repairs.
Until the late 196Os, Japanese engineers designed buildings to be more rigid than their counterparts in California, says Andrei Reinhorn of the National Centre for Earthquake Engineering Research, based at the State University of New York at Buffalo. This made the buildings more likely to ride out moderate earthquakes without damage, but left them vulnerable to collapse in more severe quakes. Early indications from Kobe are that most of the buildings that failed were put up at least 25 years ago, when those standards were in force.
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More modern Japanese regulations call for buildings to be made strong enough to resist damage in moderate quakes and also to incorporate failure points that break in severe quakes to prevent total collapse. As a result, says Reinhorn, modern Japanese buildings should perform just as well as Californian ones in a large earthquake and suffer less damage in medium-sized ones.
As earthquake engineers from both countries examine Kobe鈥檚 buildings over the next few months, they will learn how well the new designs actually fared, says Yan Xiao, a structural engineer at the University of Southern California, who set off for Kobe last weekend.
Even if Japan鈥檚 preference for rigid buildings back in the 195Os and 196Os left it vulnerable to a disaster such as last week鈥檚 earthquake, American earthquake experts realise they have no reason to feel smug. Last year鈥檚 Northridge earthquake caused relatively little havoc because it happened in the San Fernando Valley, where there are few old buildings, says George Housner, professor emeritus of civil engineering at the California Institute of Technology. 鈥淚f the Northridge quake had occurred 40 kilometres further south, under the old portion of Los Angeles,鈥� he says, 鈥渨e would have had a lot more collapsed buildings.鈥�