Goo in walls to absorb quake shock
Japanese system used at hospital
The new California Pacific Medical Center under construction on Van Ness Avenue has installed an earthquake shock absorber system built around a goo-like substance with the consistency (and stickiness) of a wad of chewed bubble gum.
The $2 billion, 274-bed hospital is the first building in the U.S. to use a technology called viscous wall dampers, with goo-filled panels embedded inside the hospital walls.
The system was originally developed in Japan 20 years ago, and buildings that used it survived temblors like the 9.0 Tokoku quake in 2011. After years of testing by engineering experts in California, designers believe the goo inside the walls of the new hospital will help it remain open after an event as strong as the 7.8 magnitude 1906 earthquake.
“You’re going to feel that you’re in an earthquake — you can’t stop the entire earthquake,” said Jay Love, senior principal with Degenkolb Engineers, the Oakland structural engineering firm for the project. “The building will still sway back
and forth, but it will be more of a gentle sway rather than a bumpy sway.”
Pedestrians walking past the construction site between Van Ness Avenue and Franklin Street might notice some of the 119 burgundy-colored wall panels installed on several floors of the hospital’s 12-story skeleton.
Those 7-foot-wide panels are essentially steel tanks filled with a 20-millimeter-thick synthetic rubber substance, polyisobutylene. Steel blades connected to floor beams above and below the walls run through the opaque rubber.
During a severe quake, the polyisobutylene resists the movement of the blades inside the panels, thus keeping the attached floor beams from also moving about wildly. Love said tests showed the system should absorb about 80 to 90 percent of the energy a quake generates.
“If you can imagine riding in your car without shock absorbers, you’re going to feel every bump,” he said. “With the shock absorbers, it evens (the bumps) out.”
The system wouldn’t eliminate all damage to the building or its contents, but is designed to keep the hospital operational in a magnitude 7.9 quake on the San Andreas Fault.
The viscous walls were picked over more common seismic base isolation systems because of the complexity of the construction site, including the need for about 250,000 square feet of parking and storage below ground. The 25-acre site of the old Jack Tar Hotel also slopes down about 45 feet between Franklin Street and Van Ness, and is tilted between Post Street and Geary Boulevard.
The viscous system allowed engineers to use about one-third less steel for seismic bracing below ground level. “We got back the space we would have lost because of the base isolators,” Love said.
But the system also increased costs. Tests of the plan for the new medical center began at UC San Diego’s seismic test facility in 2007, about six years before construction began. The system must meet stringent California Office of Statewide Health Planning and Development standards for hospital construction.
The hospital, operated by Sutter Health, has installed viscous wall panels on all sides of the building, fitted between what will be room windows. They’ll eventually be invisible, except one inside the hospital in case engineers need to conduct future tests.
Degenkolb Engineers worked with Dynamic Isolation Systems, a McCarran, Nev., company that is marketing the technology for use in the U.S. in other structures that might be built in areas affected by quakes or wind.
While the medical center is drawing attention to the technology, no other U.S. building projects have committed to using the wall dampers. “Nothing has gone into a final design or pricing stage,” said Kevin Friskel, a senior engineer at the Nevada company.
The system has been in use for about 20 years, mostly in buildings in Japan, but some in New Zealand, Chile and Mexico, Friskel said. About 20 of those buildings have weathered a major quake and “we have never had a collapse,” he said.
“You can’t stop the entire earthquake ... but it will be more of a gentle sway rather than a bumpy sway.” Jay Love, senior principal with Degenkolb Engineers of Oakland