A team of Stanford engineers have built and tested an earthquake-resistant house that sits on top of sliding “isolators” to ride out tremors. The test house, which also makes use of heavy-duty reinforcing, withstood an earthquake simulation that was three times the intensity of the Bay Area’s devastating 1989 Loma Prieta quake. The team says the modifications are inexpensive and could easily be used in new home construction where their costs would soon be offset by reduced earthquake insurance premiums.
California residential buildings are generally safe for occupants in the event of an earthquake, but quakes do a lot of costly damage to the properties, such as damage to cabinetry, windows and cladding. To build their quake-resistant home, the team borrowed the notion of a “unibody” from the auto industry, with each part of the test house being important to its structural integrity. Thicker drywall sheets are glued rather than screwed to the framework, for example. The engineers then placed the test house on 12 steel and plastic sliders instead of a fixed foundation. The sliders rest in turn on either galvanized steel plates or dishes and the house slides from side to side during a tremor, in a process known as “seismic isolation.” The flat plate design is easier to make, but the dish design means the isolator pegs gravitate to the lowest part of the dish once the seismic event is over, returning the house to its original position.
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Co-lead of the project Eduardo Miranda notes: “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.” Large seismic isolation systems are already in place at San Francisco City Hall and some buildings at the San Francisco International Airport. However, these systems are expensive. By scaling-down and using inexpensive materials, the team estimate their design would cost around $10,000 to $15,000 for a 1,500- to 2,000-square-foot house and take four days of additional labor.
Of course, the fun part of the team’s endeavor was the testing. The team took their test house to the University of California, San Diego’s Large High Performance Outdoor Shake Table. The table is able to replicate the behavior of earthquakes such as the Loma Prieta event. After the house had withstood three times the ground shake intensity of that quake, the team removed the isolators and turned the table up to 11 to see how much the reinforced structure could handle on its own. It outperformed all expectations, but eventually sustained damage at the table’s highest setting. Of the success, project co-lead Gregory Deierlein said, “We are always cautious never to talk about earthquake-proof, but our resistance is getting better and better.”
Via Stanford News
Photos by Martin Luff via Flickr and screengrab by Stanford via YouTube