Seismic Design Hailed for Averting Hospital Damage : Safety: Base isolation system is credited with lessening impact of Northridge quake on USC facility.
The terrifying jolt that woke most of Southern California on Jan. 17 felt like nothing more than a gentle rocking at USC University Hospital in Los Angeles, with some patients saying that it was as if they were babies again, back in their cradles.
In other hospitals, chaos ensued. Water cascaded from fire sprinkler systems. Power failed. Breathing apparatuses wheezed to a halt. Glass shattered. In all, a dozen hospitals, some of them built to modern seismic standards, had to close or curtail patient services.
Part of the difference, experts agree, was a state-of-the-art seismic safety system built into USC University Hospital’s foundation. The so-called base isolation system--designed to work much like the springs and shock absorbers on an automobile--absorbed or damped about two-thirds of the force that hit the eight-story building.
Opened in 1991 as the nation’s first base-isolated hospital, USC University Hospital’s performance in the Northridge quake is being hailed by some engineers as proof positive of the technology’s potential for protecting all types of critical structures, from fire stations to businesses’ computer centers and their contents.
Some caution that the structure was too far from the epicenter to be subjected to more than moderate shaking and that questions remain about how such systems would function in a large quake. Even so, it is clear that this real-world test of base isolation is gaining converts to the notion of preventing buildings from shaking rather than only trying to build them strong enough to remain standing after being tossed about.
“Everybody’s eyes lit up with that, and now all of the vendors are saying, ‘Look, told you so, base isolation works,’ ” said Bill Staehlin, supervising structural engineer for the Office of Statewide Health Planning and Development, the state agency that oversees hospital construction.
Modern buildings are supposed to withstand even the most powerful of earthquakes, but base-isolation systems offer the added benefit of protecting equipment, water lines and other contents so that structures remain functional, Staehlin said.
While engineers analyze $13 billion in damage to freeways, parking structures, steel-frame office towers, wood-frame apartment buildings and tilt-up concrete warehouses and try to understand their weaknesses, some researchers and policy-makers are urging greater emphasis on preventing some of the damage in the first place.
Among the techniques being researched are the use of mechanical devices to counteract the force of an earthquake and installation of friction plates that let buildings slide side to side. By far the most promising approach, and the only one that is actually installed in more than just a handful of buildings, is that of base isolators, engineers said.
Caltech civil engineering professor John F. Hall testified recently at a congressional hearing that although more research is needed, base isolation is “the right road to be going down” for protecting hospitals, emergency command centers and other structures that must remain functional after an earthquake.
Only about 300 buildings and bridges worldwide--80 buildings nationally--use the technology. But at least a dozen more buildings and several bridges are being built or retrofitted with isolators in California, even though they can cost tens of millions of dollars.
One of those will be a five-floor hospital within a hospital proposed as part of a replacement for the aging Los Angeles County-USC Medical Center. The facility, which would contain the trauma care center, surgery theaters, radiology rooms and laboratory, is already known as “the lifeboat.”
With doctors and nurses there likely to see scores of injured people after a magnitude 8.0 earthquake, the 300,000-square-foot, critical-care facility would have three days’ worth of water, power and medicine in reserve. More important, it is to be built on a series of steel, rubber and lead pads that will help make sure the equipment and supplies survive.
The current county medical center, which includes 100 mostly old, seismically unsafe buildings, suffered nearly $400 million in damage in the Northridge quake. Two of the center’s four hospitals remain closed, and 16 or more other buildings will have to be demolished.
But even modern hospitals were put out of commission by the quake. Olive View-UCLA Medical Center, a stiffly built steel-frame building erected in 1987 to replace an older structure destroyed in the 1971 Sylmar earthquake, was not damaged structurally, but shaking ruptured a water main and caused the hospital’s fire sprinklers to leak. The facility had to be shut down for several days.
In hopes of avoiding such a scenario, San Bernardino County officials are planning a base isolation system for the foundation of a new $434-million, 835,000-square-foot medical center to be built in Colton, near the San Andreas and San Jacinto faults. Those faults are thought to be capable of producing magnitude 8.0 or greater quakes, county Deputy Administrative Officer John Giblin said.
“We . . . realized that if there is a major seismic event, there are not going to be very many hospitals in this valley that are operating . . . because of their age and the way they are built,” Giblin said.
“We could build the hospital to withstand an earthquake, but . . . what’s inside the hospital is not going to be in very good shape,” he said.
The concept of base isolation is tantalizingly simple and goes back nearly a century: Just as springs and shock absorbers smooth out the ride in a car, base isolators soften the seismic impact.
But the hardware had to be invented and tested, and computer models had to be developed to analyze how buildings with isolators would perform in a quake, said Ron Mayes, president of Dynamic Isolation Systems in Berkeley, designer of the system at the privately owned USC University Hospital.
Some engineers say that more research is needed and that builders should be cautious about recommending widespread installation of the systems.
Thomas Heaton, a U.S. Geological Service seismologist based in Pasadena, agreed that the system worked at USC University Hospital. But he said: “Unfortunately, the ground shaking at USC was much smaller than what can be expected in close, very large earthquakes . . . so it was probably not the ultimate test.”
He calculated that the hospital’s base isolators would have been pushed beyond their ability to absorb energy if the structure had been located in the northeast Valley, where longer waves of more intense motion were recorded.
Some even speculate that in the largest quakes, base isolators could actually amplify building movement. So far, however, the systems have only been subjected to moderate quakes and generally have performed as designed.
The first base-isolated building in the United States, the Foothill Communities Law and Justice Center in Rancho Cucamonga, opened in 1986 and houses courtrooms and offices of the district attorney, public defender and the San Bernardino County Sheriff. In the magnitude 5.5 Upland earthquake in 1990, the base isolation system absorbed about half of the force exerted, leaving the building’s contents undamaged.
Base isolation has also been used in the construction and retrofitting of bridges, utility lines and sensitive equipment, such as parts of the Stanford Linear Accelerator experimental physics facility in Palo Alto.
The system has been installed in some buildings that are critical for emergency response, including the Los Angeles County Fire Command and Control Facility, and some that house expensive equipment or crucial computerized data, including the Kaiser Permanente Regional Data Center in Corona.
The Northridge quake exposed a flaw in the construction of the Fire Command Center, experts said. To work properly, isolation systems have to move freely and a moat of sorts is normally built to give the building room to rock. But the command center was connected to the ground with a layer of concrete that bridged the moat, which caused shaking inside to increase for a moment or so until the concrete was broken away by the quake’s force.
Base isolation has also been used to make historic buildings less vulnerable to an earthquake without obscuring their distinctive architectural features. For example, a $21-million base isolation system is being installed at UCLA’s Kerckhoff Hall, which was built in 1929 and is one of the oldest buildings on campus.
Los Angeles City Hall, and city halls in San Francisco and Oakland that were damaged in the 1989 Loma Prieta quake, will be renovated with the technology.
In some cases, such as the county Fire Command Center, base isolation can actually reduce building costs because other parts of the structure can be made lighter, experts said. But the system also can add 1% to 4% to construction costs. Mayes said even that relatively small premium is enough to discourage many owners.
“When you haven’t had a major event for 20 years, you forget” how devastating a quake can be, he said. “It’s only at a time like this that you realize that it’s a minuscule cost to society.”
What is needed, Mayes and others said, is for the state and federal governments to foster efforts to prevent earthquake damage by granting tax incentives to encourage retrofitting and by pushing changes in building codes to emphasize saving structures as well as lives.
Michael P. Bocchicchio, assistant vice president for facilities for the University of California system and a former state architect, agreed. “With the tremendous amount of damage we experienced in the Northridge quake, we ought to be starting to think about the socioeconomic aspects of quake damage as well as life safety,” he said. “It becomes a question of whether the society as a whole can withstand . . . a major disaster in which the economy takes a real hit and you have people without homes, businesses, jobs.”
State Sen. Don Rogers (R-Tehachapi) has carried several pieces of legislation to encourage the use of earthquake hazard mitigation measures, including base isolation.
“We seem to always react when it comes to earthquakes,” he said. “Before the earthquake occurs, we should be very busy using this technology so that when the earthquake occurs, you have eliminated most of the damage.”
* MAKING CITY HALL SAFE: Retrofitting a landmark. B2