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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.

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