Earthquake-resistant house built, tested

Stanford engineers have designed and built an earthquake-resistant two-story house which can withstand destructive tremors and shakes.
The house stayed staunchly upright even as it shook at three times the intensity of the 6.9 magnitude destructive 1989 Loma Prieta temblor in northern California, researchers said.
The engineers outfitted their scaled-down, boxy house with sliding "isolators" so it skated along the trembling ground instead of collapsing.
They included extra-strength walls to create a home that might replace the need for residential earthquake insurance, said project leader Gregory Deierlein, Stanford University's John A Blume Professor in the School of Engineering.
The modifications are inexpensive and could be incorporated into new homes as soon as designers and contractors decide to try them, according to the researchers.

"We want a house that is damage free after the big earthquake," said Eduardo Miranda, an associate professor of civil and environmental engineering.

Residential homes already do a good job of keeping the people inside safe when a temblor hits. But earthquakes typically do a lot of minor structural damage.
Even if the walls stay up in a quake, wall finishes like drywall and stucco, along with architectural fixtures like cabinetry, are damaged because of the large sideways movements caused by earthquakes, Deierlein said.
The house that Stanford built had two major modifications to stave off earthquake damage. For one, it was not affixed into a foundation, but rested on a dozen steel-and-plastic sliders, each about 4.5 inches in diameter.

Under those sliders were either plates or bowl-shaped dishes made of galvanised steel. These units are called seismic isolators.
"The idea of seismic isolation is to isolate the house from the vibration of the ground. When the ground is moving, the house will just slide," Miranda said.
Seismic isolators already protect large structures like but they are quite expensive. The team adapted the technology for residential use by incorporating inexpensive materials into their scaled-down isolators.
The engineers developed what they call a "unibody" design, a term borrowed from the automobile industry, in which every element of the structure contributes to its strength.

Instead of simply screwing drywall to the wood framing, as in typical construction, they used glue to affix extra-thick, 5/8-inch drywall more securely.
On the outside, they used strong mesh and additional screws to attach the white stucco tightly. These elements made the house stiffer and stronger, leading to a significantly better seismic performance.