UCSD Quake-Safety System Urged : Plan Would Solve Seismic Problems at Medical Center
A highly experimental engineering system, untested as yet in the United States, is being proposed to solve longstanding seismic problems at the nationally renowned UC San Diego Medical Center.
Since UC engineers first studied the center’s main building during the late 1970s, it has been known to be at substantial risk for severe damage and possible injury to occupants during a major earthquake.
UCSD officials approved a $2-million proposal this month and submitted it to statewide university budget planners in Berkeley for consideration later this year. It is their preferred solution for improving the hospital’s safety and for allowing it to function even after a damaging temblor.
The plan in essence involves retrofitting the building with mechanical devices that would separate its seismically weak portions from the damaging effects of strong ground motion caused by earthquakes. California structural engineers believe the concept, which was developed in New Zealand, is valid as a result of scale-model testing at UC Berkeley.
However, the concept, known as base isolation, has never been used to bring an existing unsound building up to safety standards. It is part of a new four-story county government building nearing completion in San Bernardino and is under study statewide by state and professional structural engineering committees because of its potential to enhance safety at a lower cost.
“The owner of any building runs a risk if he or she designs strictly to (the uniform building) code because the code does not really provide adequate protection during a major quake,” said James Kelly, professor of engineering at UC Berkeley and the acknowledged American expert on base isolation. “The cheapest way to get additional protection above the code is to use base isolation--because in general, building beyond the code is very expensive.”
Kelly, who designed the equipment for the San Bernardino building, said that base isolation is not well-known or well-accepted by designers because only a few buildings worldwide use it and none of those structures has yet experienced a major temblor. For that reason, he said, UC officials should proceed cautiously to make certain that the technique will work on the hospital.
That caution was emphasized by the consultant who drew up the retrofitting plan.
“It’s the preferred solution, but only one of several until we work out a detailed analysis on the building,” said consultant Walt Saunders, a structural engineer in Costa Mesa. “Our schematic findings show it is viable, but now we have to put into a computer specific earthquake data for the site and the hospital’s physical characteristics and come up with a model.
“We could find this won’t solve all the problems as we hope.”
Medical center officials nevertheless are eager to have computer modeling validate the concept so they can end years of uncertainty over the hospital’s fate. UCSD campus architect Charles Powers said that, although he believes the hospital would not collapse unless a devastating quake unforeseen for the San Diego area were to take place, the structure nevertheless needs improvement.
The center’s main building, a nine-story tower set on a wider three-story base structure, was constructed in 1961 as a county hospital and exceeded the minimum earthquake codes at the time. However, the code has since been changed substantially as a result of lessons learned during various quakes, and the building was identified as a potential seismic risk to workers and patients during UC engineering studies in the late 1970s.
When the UC system bought the hospital in 1981, retrofitting was made part of the purchase agreement between the state and the county. An initial two-year engineering study endorsed a conventional mode of strengthening the building’s ability to survive strong shaking without crumbling by sheathing it with a steel frame.
That sheathing would have cost an estimated $5.3 million, plus $4 million or so that would have to paid to relocate various medical functions temporarily because of the construction work. That plan was rejected both because of complaints about the cost by university budget planners and concerns locally about aesthetics.
“There was the money involved and also the expected look of the steel bracing, which is steel you let out in the elements to eventually turn rust-colored,” said Ron Dowd, the medical center’s director of facilities management.
Administrators asked for a second study, which resulted in the Saunders recommendation last month for base isolation.
The base isolation concept reduces the amount of energy transferred into a structure from an earthquake by using, for example, a series of bearings composed of rubber layered between multiple steel plates. Placed at columns and walls, the components of the system would allow for vertical and lateral movements during a quake and at the same time absorb most of a temblor’s energy, substantially reducing the building’s movements.
The conventional means of protecting a building involves buttressing its ability to withstand otherwise damaging shaking through reinforced columns, walls and beams. A potential added benefit of base isolation includes protection of a building’s contents from the effects of a temblor. Such protection ordinarily must be provided for separately by tying down bookcases, computers and other furnishings.
Saunders proposes isolating the tower from the hospital’s base at the third floor. “Of course, the acid test will be when the building is modeled” in the computer, Saunders said. “But our schematic shows the building is a viable candidate because you don’t have to isolate the entire structure but only the portion (rising) from the third-floor base.”
San Francisco structural engineer Alex Tarics said the technique works best in bulky buildings that are 3 to 10 stories high, have valuable contents and must function after a quake. Tarics worked on the San Bernardino building.
The proposal must be reviewed at numerous levels: by planners at the UC president’s office in Berkeley, by the Office of the State Architect and by the Office of Statewide Health Planning and Development.
“I can promise you that there will be very, very thorough reviews,” said structural engineer William Holmes of San Francisco, who sits on state and professional committees that are drawing up guidelines for incorporating base isolation into the uniform building code. A unique aspect of the UCSD proposal is the projected use of base isolation on an existing building.
“I like to see a fail-safe mechanism in these things so that if there is a quake unforeseen by our studies, the building would still not collapse,” said George Housner, a Caltech professor who served on a review committee for the San Bernardino building. Housner said that a fail-safe mechanism might be far more difficult to design for an existing building that has been retrofitted with base isolation but otherwise remains unchanged. If the base isolation were to fail, the building would behave as if no improvements had been made.
If base isolation is not approved for the medical center, Saunders has included in his report an alternative retrofit using new steel braces in the hospital’s interior. But that alternative, although somewhat cheaper than base isolation, would not bring the hospital up to present life-safety codes and would not ensure its continued functioning after a major quake. It would represent an improvement from present circumstances by creating a larger margin of safety for patients and workers to evacuate it safely.