Among the numerous cavernous buildings at the former Navy shipyard on Vallejo’s Mare Island is the home of Earthquake Protection Systems.
For more than a quarter century, it has been manufacturing special bearings that allow office buildings, bridges, elevated highways, hospitals, power plants and other critical infrastructure to ride out major earthquakes with so little damage that they’re able to continue functioning immediately after a disaster. And demand for the systems has kept EPS on the move to ever-larger facilities around the Bay Area. Now, the company is gearing up to expand yet again.
EPS’s main product are Friction Pendulum seismic isolators, invented and later patented after the founder’s postdoctoral engineering studies in the years after a devastating California earthquake.
“This is very different from the building code requirement, which only seeks to prevent collapse,” said Victor Zayas, Ph.D., P.E., president and founder of EPS, which he started in 1985. “We seek to minimize damage, so that hospitals can stay functioning, power plants can stay functioning, highways can stay open, railways can keep running.”
Helping a structure move during a temblor in a controlled, predictable way is the job of base isolators such as EPS’s friction bearing. They lessen the motion of the moving ground (substructure) that’s transferred to the building or bridge (superstructure). Other variations of base isolators include elastomeric bearings, which have layers of steel and rubber around a lead core; spring bearings with dampers; and roller bearings.
Base isolation is a technology that is commonly used for structures that are needed for postearthquake response and recovery, such as hospitals and emergency operations centers, according to James O. Malley, S.E., San Francisco-based group director and senior principal for Degenkolb Engineers.
Other applications of the technology are for special-use structures such as art museums, because of their priceless and fragile contents, and data centers, because of the value of the equipment and goal of staying in operations after a quake, Malley said. Key historical or architectural building also have been put into such isolation, namely city halls in San Francisco, Oakland and Salt Lake City.
Use of damping technology is another mechanism for improving seismic performance of structures, Malley said. Damper technology is sometimes used in conjunction with base isolation, when the site to be protected is quite large, Malley said. Types of dampers include viscous (like shock-absorbers in a car), friction, yielding (roughly like crash crumple zones in automobiles) and tuned mass.
DIFFERENT ENGINEERING REQUIRED
It is not complex science, Zayas said.
"But it is somewhat detailed engineering that is different from what most know how to do,” he said. That’s because the isolator design used has to be matched with the superstructure design, else the bearing will be less than effective, he said.
“When you apply these isolators to structures built under existing code, you increase the risk of collapse by a factor of 10 to 20,” Zayas said.
In 2006, a triple Friction Pendulum isolator was developed to control the motion further. The concept for the isolator is that the building sits on a pedestal in the center of a concave metal bowl, and the specially designed friction between the pedestal moving on the sides of the bowl lessens the quake energy transferred to the superstructure.
EPS also offers a tension friction isolator, which limits up and down movement that can happen during quakes and with the sloped surfaces of the pendulum bearings.