Simpson Strong Tie lead engineer Steve Pryor has been to Miki City, Japan, some five times over the past year assisting in the construction of a seven-story multifamily building featuring 23 one- and two- bedroom units and space for two retail shops. On June 19, Pryor heads back to Miki City a final time, not for a month-long lease-up but for the ultimate shakedown: a series of increasingly violent earthquake simulations that could bring the brand-new apartment tower down in virtually seconds. “One of the realities of seismic testing is that you spend a lot of time and effort building something, and then an earthquake simulation will last 30 or 40 seconds, and you’re done,” Pryor says.
Funded in part by a $1.4 million grant from the National Science Foundation (NSF), the NEESWood Capstone tests are a collaborative effort between Simpson Strong Tie and major engineering universities, including Colorado State and Texas A&M, to develop new design approaches for taller wood-frame buildings in urban, earthquake-prone areas. The results could also have wide-reaching effects on future multifamily design philosophies, approaches to property management during crises, and even the application of renter’s insurance in earthquake prone areas.
Working at Simpson Strong Tie’s headquarters in Livermore, Calif., some 10 miles from the volatile Hayward, Calif., fault line, Pryor is all too familiar with the destructive power of earthquakes in the San Francisco Bay Area. Pryor’s not alone: The NSF estimates that more than 75 million Americans in 39 states live in towns and cities considered at risk for earthquake devastation. In California alone, earthquakes are expected to create $33 billion in property damage over the next 10 years, according to the California Geological Survey.
But at the test site in Japan, Pryor does not expect a collapse. On the contrary, construction of the apartment tower at Miki City’s Hyogo Earthquake Engineering Research Center (code-named “E-Defense”) is intended to determine new ways to prevent the occurrence of building collapse during large-scale seismic events. The E-Defense, full-scale 3D earthquake testing facility features a shake table measuring 65-by-49 feet that can support building experiments weighing up to 2.5 million pounds, and will be used to subject the test building to earthquakes as large as the 6.7 Northridge quake that decimated parts of Los Angeles in 1994.
And while finding ways to prevent such catastrophic damage is obviously laudable, property assurance is not the central focus of the upcoming Capstone shakes. “The minimum performance level is noncollapse,” Pryor says. “There can be significant movement and significant damage, but the preservation of life is our principal measurement, and the primary goal therefore is to not collapse the building.”
To succeed, Pryor and other Capstone engineers will have to get their building through a series of three shakes. On June 30, the whole structure will be subject to two levels of shaking: one moderate warm-up shake followed by a “design level earthquake,” something that might on average occur every 475 years. On July 6, the team continues the testing with a bracing system that takes the steel frame of the building out of participation of the movement, so the shaking will be experienced by just the wood-framed structure only. On July 14, a final test will involve increasing the shaking by almost 50 percent. “It will be representative of what is called a ‘maximum considered’ earthquake,” Pryor says. “It’s a very large quake that statistically might be seen only every 2,500 years or so.”
Sound remote? To put the huge shake into context, consider that it represents an earthquake that has a 2 percent chance of occurring underneath a multifamily building with a 50-year life span. “It’s still a low probability event,” Pryor explains. “But the risk to society is clearly very large if you don’t design for that.”
Pryor was involved in constructing the foundation of the building with Japanese ironworkers, installing Simpson Strong Tie Special Moment Frames, huge steel connectors that anchor the structure to its foundation. Video cameras inside furnished units and outside of the building will capture the action during the tests and will be used in conjunction with seismic and structural data to analyze the results.
“I’d be lying if I said I didn’t have butterflies, but in reality, from a structural engineering standpoint, we have our modeling, and only our best guess estimates of what is going to happen, Pryor says. “If we knew with certainty what was going to happen, there would be no reason to test.”
Simpson Strong Tie intends to make video footage of the tests available shortly after completion of the shake series. YouTube features video footage of similar E-Defense shakes.