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Shake test: the University of California at San Diego set out to measure the survivability of a fully equipped five-story "hospital" under the force of some of the world's most intense recorded earthquakes.

In January 1994 the earthquake nightmare that had long afflicted California's healthcare system came true: A 6.7-magnitude quake left 11 Los Angeles-area hospitals partially unfit for occupation and caused $3 billion in damage.

The next year, California enacted legislation putting hospitals on a strict schedule for upgrading structures particularly vulnerable to earthquakes. Though modified in 2010 to more scientifically define the highest-risk Structural Performance Category-1 structures, in effect reducing their number from 40% to 20% of hospitals and extending compliance deadlines throughout the next decade, numerous structures are still reported to be in danger of collapse from a major earthquake-40 hospital buildings in San Bernardino County alone, according to a Center for Health Reporting article published in 2011. Some 225 hospitals are under state mandate to report compliance progress for campuses having at least one building in danger of collapse, according to the state Office of Statewide Health Planning and Development (OSH.PD). Yet hospitals, along with the rest of California's economy, are struggling with financial shortfalls threatening completion of needed capital improvements.

With California facing a one in tour chance of an earthquake of 6.7 or greater occurring during the next decade, according to a U.S. Geological Survey estimate, hospitals are in need of accurate information that can be used to adequately protect their buildings in a timely fashion despite Fiscal austerity.

Enter a unique five-story "hospital" constructed atop a 7.6-meter-by-12.2-meter shake table designed to reproduce motions recorded or scaled from recent intense quakes ranging from 6.7 (Los Angeles) to 8.0 (Peru, 2007) to 8.8 (Chile, 2010). Under the auspices of the University of California at San Diego's (UCSD) Englekirk Structural Engineering Center, this was the largest shake table-based structure ever to focus on nonstructural component function and survivability post-earthquake. It featured two upper stories housing a fully equipped surgical suite and intensive care unit, as well as floors including furnishings and equipment both secured and unsecured, piping and conduits for HVAC, plumbing and electricity, a small network of computer servers and workstations, and a fully operational fire suppression system. The building also featured standard egress via an elevator and stairway, 8-inch concrete slab flooring, and two types of cladding: precast concrete for the top two floors and lightweight metal studs overlaid with gypsum and stucco below.

The structure was put to the test in April and May 2012, first through a progressively vigorous shaking with and without base isolation, then with a controlled burn simulating a post-quake fire. The shaking encompassed a series of one-way thrusts eventually reaching as much as eight times horizontal gravity load. With base isolators--flexible rubber mountings that can reduce horizontal motion in the building--the horizontal acceleration of the building was reduced to about a quarter of that experienced under the fixed condition. The shaking was resumed minus the isolators, leading to dramatically eye-opening results, and was followed by the controlled burn test.

The aftermath produced mixed feelings for the engineers, industry product suppliers, and state regulators involved in this multiyear collaboration. They were pleased by access to real-world experimental data they had never had before--data going far beyond standard post-quake assessments and expensive computer modeling. But they were both reassured and sobered by the immediate findings. They are just now starting to sift through the massive data sets the testing produced, a process that is expected to continue for years to come. But they were willing to discuss at least some preliminary lessons that emerged.

For one thing, one major finding is already established: Base isolation contributes significantly to building safety and Functioning, even after the more severe quakes. The structure's facade remained intact and the interior contents and infrastructure largely undisturbed, even after the severest shaking. "The building would have remained occupied and operational with base isolation," says Tara Hutchinson, professor of engineering at UCSD and project principal investigator. However, she notes, a base isolation retrofit for vulnerable hospitals could be prohibitively expensive. "Although we were able to install and remove base isolators from this test structure," Hutchinson says, "you would need a relatively large moat around the hospital if it was base-isolated, and that in itself could be too costly." As the situation stands now, only 30 buildings in all of California are base-isolated, including two hospitals: the Mills-Peninsula Medical Center in Burlingame and the women's health center at Hoag Memorial Hospital in Newport Beach.

Nonstructural components that performed relatively well until the last and most severe stages of shaking included the elevator, the electrical system, the computer servers, and the roof-mounted equipment. As for stabilizing hardware for HVAC and patient beds, corporate partner on the project Hilti found the initial results to be reassuring, says David Crawford, technical marketing director. "This test reaffirmed earlier test data and, in general, strengthens our foundations for seismic design recommendations. But we'll be scrutinizing the photos and data sets for a long time with an eye toward improvements.

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Once the base isolators were removed, several nonstructural components were severely affected, including the egress stairway and unsecured patient beds and shelving. According to Hutchinson, the standard prefabricated metal stairway separated from the building at the landings, while unsecured beds smashed holes in drywall partitions and unsecured refrigerators toppled dangerously.

Follow-up studies that will interpret how the building responded to the earthquake and fire tests will soon provide "tremendous insights," says Fred Turner, staff structural engineer at the state's Alfred E. Alquist Seismic Safety Commission. "UCSD is finding that some of its computer-generated estimates of building damage thresholds weren't very accurate in some respects. For example, as damage propagated through the building, it took unpredicted paths and showed up as failures in surprising areas. On the other hand, the burn testing confirmed that shake-related damage exacerbated smoke and flame spreads. It revealed separations in the wall and floor connections opening up fire pathways we didn't anticipate. Building connections like these are critical, yet architects often leave their detailing up to contractors. We hope to be better able to advise designers on these issues once we've secured more data.

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"For now," Turner continues, "I think the lesson is to investigate post-quake damage more deeply than we've been accustomed to. Cracks that may seem largely cosmetic may in fact require lifting ceiling tiles and going beneath walls and slabs to further investigate, because the true extent of damage can be quite sobering."

The next several years will see the accumulated shake and fire test results spread throughout California's regulatory, manufacturing, and hospital operational communities. It's anticipated that improved national regulations will develop, new and improved products will emerge, and hospitals will find ways to implement retrofit and replacement projects aimed at bringing most of them into compliance with California seismic law. However, it's unknown whether this will happen before the next "big one" hits.

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Seismic implications spread much farther than the boundaries of the Golden State. In fact, there are several seismic-sensitive areas of the United States that are not nearly as far along as California in preparing for inevitable major quakes. Chris Poland, SE, chairman and CEO of San Francisco-based Degenkolb Engineers, says that on travels throughout the United States, he has seen several potential trouble locations.

"Memphis, Tennessee, for example, which has experienced severe quakes, is still not building to modern standards because, although they have a new code, it is still not enforced. South Carolina and the nearby coastal region adopted new codes only recently, with 90% to 95% of their buildings having been constructed without regard to earthquake potential. Salt Lake City and areas in western Tennessee are the most critical of all--they're going to see major damage unless they quickly develop a new construction culture.

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For more information on UCSD's Englekirk Structural Engineering Center, please visit http://www.jacobsschool.ucsd.edu/Englekirk.

By Richard L. Peck; Images courtesy of Jacobs School of Engineering at UC San Diego
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Title Annotation:FEATURE
Author:Peck, Richard L.
Publication:Healthcare Design
Geographic Code:1U9CA
Date:Aug 1, 2012
Words:1326
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