In 1989, California's central coast was rocked by a 6.9 magnitude earthquake, destroying infrastructure and buildings in San Francisco, Oakland, and a host of coastal cities. The Loma Prieta Earthquake caused an estimated $6 trillion in damage, prompting researchers to develop techniques for management of severe seismic activity in urban centres. Twenty five years later, a team of engineers at Stanford University have invented a cost-effective foundation for residential buildings capable of withstanding three times the magnitude of the catastrophic 1989 earthquake.
Find out more on Stanford's earthquake-resistant technology after the break
Of the estimated 10,000 earthquakes California receives annually, approximately 15-20 are capable of producing serious damage to millions of structures across the state. Earthquake insurance is levied on homeowners to offset costs associated with major reconstruction of infrastructure and housing, costing homeowners an average of $673 annually. The team of engineers at Stanford set about to develop a foundation that could withstand California's harshest seismic activity, potentially bringing a significant reduction in the costs of insurance. The resulting home utilizes automotive unibody technology to create a reinforced structure able to endure some of the strongest earthquakes likely in California.
The premise behind the technology is simple: "When the ground is moving, the house will just slide," says Edouardo Miranda, an associate professor of engineering at Stanford. During an earthquake, the house would skate along a series of "isolators," 4.5 inch steel and plastic sliders resting atop bowl-shaped dishes of galvanized steel, minimizing the destructive effects of intense structural vibration. When combined with the unibody structural frame, the isolators minimize vibration from the ground, eliminating the destructive effects created by earthquakes. The technology is similar to the seismic isolators already used on many public buildings in California, except at a dramatically lower price: researchers estimate the cost of implementing the system at only $10,000 to $15,000, adding four days to construction time. One-time installation costs pale in comparison to earthquake insurance costs, say researchers.
Tests on the structure were carried out at the University of California San Diego, home to the largest earthquake simulator in the United States. The 'shake table' measures 36' by 22' and was able accommodate the two-storey, three bedroom home constructed by the project team. Simulations were programmed based on historic earthquakes with significant residential damage, including the 1994 quake in Los Angeles damaging 500,000 homes and incurring $25.6 Billion in repair costs. The house underwent trials with and without isolators, designed to test the resiliency of the house's reinforced structure. According to Stanford, the house "outperformed" expectations during testing, and only showed structural damage upon being tested at maximum capacity by the simulator.
Stanford's earthquake-resistant technology is now ready to be implemented in zones of seismic activity worldwide, having completed and passed rigorous safety tests. Its next hurdle will be zoning approval and inclusion in residential design. Read more about the project at Stanford News.