Wood-Frame House Suffers in Simulated Earthquake
RENÉE MONTAGNE, host:
No one can predict exactly when and where in the U.S. the next big earthquake will hit. California and the Northwest are likely places. And engineers there have designed buildings to survive all but the biggest quakes.
But the quake worthiness of smaller wood-frame buildings is something of a mystery. So engineers built a two-story frame house on a huge shake table and then last fall, shook it. Morning Edition was there with a recorder to capture the moment.
Unidentified Man: We stand by as we begin.
(Soundbite of simulated earthquake)
MONTAGNE: Now, engineers have examined the house more closely. And as NPR's Christopher Joyce reports, they've got some ideas for making building codes better.
CHRISTOPHER JOYCE: The big shake took place inside a hangar-sized building at the University of Buffalo in New York. It only lasted a few seconds and it didn't seem like much happened - the roof held, the walls didn't collapse, even the windows stayed put.
But inside the house, it was a different story. The house was furnished - from a dining room set for four to a typical college student's bedroom. Microphones planted inside, recorded the bedlam.
(Soundbite of simulated earthquake in house)
It was the equivalent of a 6.7 magnitude quake, like the one that hit Northridge, California, in 1994. Andre Filiatrault, one of the engineers in charge, says the quake threw objects around with a force equal to one and a half times their weight.
Mr. ANDRE FILIATRAULT (Engineer): It would have been difficult, perhaps, to stand up during the shaking. A 150 percent your body weight is significant -pushed laterally - coupled with all the contents flying left and right. And in the dorm room, the television flew almost eight feet across the room just from that shaking, from that force.
JOYCE: As nice as it looked after the shake, this house was totaled. Here's why. Many wood frame houses are built on a concrete slab. Around the perimeter, you bolt down a piece of two by four called a sill plate. Then the walls of the house are anchored to that sill plate. During the test, the sill plate failed.
Mr. FILIATRAULT: We found that this was completely cracked all around the perimeters. So what it means, of course, if it was a real event, that building - its capability to resist an aftershock, for example, could be questionable.
JOYCE: And as far as fixing the house is concerned.
Mr. FILIATRAULT: It would probably mean that as you need to jack up the buildings, so lift the building completely, go underneath, remove this sill plate, put a new one in, and that's - in terms of economic issue, that could overwhelm an owner.
JOYCE: There were other intriguing results. Filiatrault says energy from the vibrations is carried through the walls. Large gaps, in this case, the garage door opening, don't transmit this energy. So that puts extra stress on the surrounding walls. In essence, the end of the house twisted around the garage door opening.
Filiatrault says one goal of the research is to give property owners in quake zones new building codes designed not just to save lives, but to save property as well.
Mr. FILIATRAULT: Many owners believe, wow, my building performed well. But its damaged, and economically the cost is very high. Well, you have to remember that our codes are there mainly for life safety performance objectives.
JOYCE: The engineering team is writing up its final results. They say, at the very least, homebuilders in earthquake zones might want to build a stronger sill plates and reinforce areas around large openings, and it wouldn't hurt to tie down your TV either.
Christopher Joyce, NPR News.
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