Mills-Peninsula's new hospital built to ride out an 8.5 quake without missing a beat
Imagine a six-story, 450,000-square-foot building gently riding out a major earthquake on a bed of steel bearings. As the earth beneath Mills-Peninsula’s new hospital shakes violently, the building itself will rise like a pendulum and sway.
If you go down under the nearly completed structure at the corner of Trousdale Drive and El Camino Real in Burlingame, you will see the bearing units sandwiched between the building and 171 columns that connect it to
the ground.
“The hospital is actually sitting on these base isolators,” says Larry Kollerer, senior project manager for the new Mills-Peninsula Medical Center.
“If you had a crane large enough, you could lift the entire building up into the air.”
During a quake
The base isolators are made of triple concave bearings – picture two highly-polished dog dishes facing each other to enclose a puck-like bearing, which itself encloses a second, smaller bearing. When a major earthquake hits, the building slides on the bearings in a gentle motion independent of the shaking of the earth.
“At Richter scale magnitude 4, the base isolators become active and isolate the hospital from the effects of a greater than 4 quake,” Kollerer explains. “Post-quake the building weight resettles, driving the bearings back to center.”
The entire building can move almost three feet in any direction. In fact, a 30-inch moat was built around the hospital to allow for that movement, Kollerer said.
Earthquake Protection Systems Inc. at Mare Island in Vallejo manufactured the friction pendulum bearings – the key components of the base isolation.
“We are the first hospital in California to use friction pendulum bearings,” Kollerer said.
He notes that the technology has been used on other strategic Bay Area structures such as the International Terminal at the San Francisco International Airport, the new Benicia-Martinez Bridge and a section of the
Bay Bridge.
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Safest in America
Mills-Peninsula chose base isolation technology for the new hospital back when California mandated an upgrade in earthquake safety for all hospitals, requiring that they are able to withstand a major quake and remain operational.
The recent quakes in Haiti and Chile remind us how important that is.
“Base isolation technology will ensure that the building will remain structurally sound, while all the technologies inside are protected,” Kollerer said. “It will withstand an 8.5 temblor centered in Burlingame and remain open for business as usual.”
The hospital’s proximity to the San Andreas fault line – about 1.5 miles – made it necessary to utilize one of the most sophisticated seismic technologies around, Kollerer said.
Several hospitals and a liquid natural gas plant built with similar technologies survived the recent 8.8 quake in Chile with minimal or no damage.
“Once complete, the new Medical Center will be one of the most seismically safe hospitals in the nation,” Kollerer said.
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Geofeedback
One of the conditions of approval by the state for the new hospital project was the installation of sensors on the site that provide an important source of data collection during an earthquake.
One seismic sensor placed in the ground outside the Mills-Peninsula Medical Center and 30 sensors installed in the new building will report the severity of earthquakes directly to the California Integrated Seismic Network (CISN), Kollerer said.
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Above code
While the attached medical office building does not sit on base isolators, it is built using a diagonal steel buckling brace frame that will absorb movement during a sizable quake, Kollerer explained.
California’s seismic requirements are higher for hospitals, where patients may be unable to walk out on their own, than for other medical facilities such as doctors’ offices, he said.
“However, the new medical office building and parking lot are designed above code for this area, with elasticity in the framework and the ability to be repaired while the buildings remain structurally sound.”
Kollerer is confident that when the predicted “big one” hits, Mills-Peninsula will be standing and ready to serve the community.
“We’ve done all we can to create a safe haven for medical services in the event of this kind of disaster,” he said. “In fact, we invested 5 percent of the total $618 million price of our new hospital on seismic technology that goes above and beyond requirements.”
For more new hospital highlights, visit millspeninsulanews.org.
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