A TEAM OF STANFORD ENGINEERS has devised a house that has welcome implications for future homeowners: In an earthquake, such a structure wouldn't shake on a foundation but move sideways on sliders, with little if any ill effect.
The concept of building a sliding house to reduce earthquake damage was the brainchild of Scott Swenson, PhD '14, six years ago. Now, the project is managed by doctoral students Ezra Jampole and Cristian E. Acevedo, MS '13, under the supervision of Gregory G. Deierlein, director of the John A. Blume Earthquake Engineering Center, and Eduardo Miranda, an associate professor of civil and environmental engineering.
Inspiration came partially from the automotive industry's "unibody" design, which fuses a car's body and chassis. Similarly, the earthquake-resistant house's drywall is glued to the frame and its exterior stucco attached by strong mesh and extra screws, making the structure stiffer and stronger. Instead of fixing the house to a foundation, the engineers raised it off the ground by attaching steel-and-plastic sliders that sit on bowl-shaped "isolators." "The idea of seismic isolation is to isolate the house from the vibration of the ground," Miranda explains. "When the ground is moving, the house will just slide."
After seven weeks of building, in September the engineers tested the house using UC-San Diego's Large High Performance Outdoor Shake Table, the biggest earthquake simulator in the country. The facility uses computer-controlled hydraulic pistons to move the platform under the house in whatever patterns the engineers specify, so it can replicate individual earthquakes like the 1989 Loma Prieta temblor.
When they shook the platform at three times the intensity of Loma Prieta (which registered 6.9 on the Richter scale), their 36-by-22-foot three-bedroom home slid laterally but held together. "The house basically saw no damage," Deierlein says. To test the unibody design alone, the engineers removed the isolators and repeated the test. A few cracks showed up in the stucco and drywall, but the house outperformed their expectations based on computer model predictions.
Seismic Isolator
Deierlein says that although it is possible to retrofit homes with these innovations, it would be easier to incorporate them in new houses. A unibody design adds a few thousand dollars at most to construction costs, and Deierlein estimates that building on seismic isolators would add about $10,000 to $15,000 to the total cost of a 1,500- to 2,000-square-foot house. By comparison, Californians paid an average annual premium of more than $700 for earthquake insurance in 2013, according to the California Department of Insurance. But the majority of homeowners don't carry a policy at all. Says Deierlein, "Ideally, insurance carriers will recognize the benefits of the enhanced performance and adjust earthquake rates to reflect the reduced risk of losses."
He is excited about being able to "help ensure that people are not displaced from their homes after a large earthquake." However, he expects it will take several years for others in the design and construction industry to work with his team to develop the new concepts and for the organizations that set building code standards to assess the designs.
Marisa Messina, '16, is a Stanford intern.
