| LAC+USC Medical Center Replacement Project Diagnostic And Treatment Building - Base Isolators |
On November 20, 2002, the Board of Supervisors approved award of a $497,883,000 contract to McCarthy/Clark/Hunt Construction Group, a joint venture (MCH), for the construction of the LAC+USC Medical Center Replacement Project. The new Medical Center will replace the existing facility, which was built in the early 1930s. The Medical Center is comprised of four main buildings - a 600-bed Inpatient Tower, a base-isolated Diagnostic & Treatment Facility (D&T), a specialty Outpatient Clinic Building, and the Central Plant.
The D&T building will be a five-story, 430,000 square-foot, base-isolated structure located between the Outpatient Department and the Inpatient Tower. It will house some of the most medically sophisticated services found in the Replacement Project including radiology, surgery, emergency services, core laboratory, inpatient pharmacy, central sterile supply, radio-pharmacy, and the trauma helipad. The D&T facility is designed with a seismic base-isolation system beneath its entire 76,650-square-foot base, and the building has been designed to be able to withstand and continue to be fully operational after a major seismic event.
Traditional building construction directly connects the building foundation to steel columns, which support beams for the floor decks and walls. In the event of an earthquake, ground motion is transferred directly into the building foundation and frame. With a base isolation structural system, the building foundation is not directly connected to the columns. The base of the building is suspended over a concrete mat foundation on isolation bearings made from layers of high-strength rubber compound bonded to steel plates. The bottom metal plate of the bearing is connected to the concrete foundation system, and the top metal plate is connected to the base of the building. There are 87 of these bearings under the D&T. They function as large shock absorbers (see picture) absorbing and dissipating the ground motion energy being transferred to the suspended first floor slab and columns. The result is a reduction of net seismic forces transmitted from the foundation through the base isolation system to the building and its components.
The design and fabrication of base isolators is a very specialized field of engineering. The isolators for the Replacement Project were made by a company in England, and had to undergo extensive testing in the factory prior to being shipped. Each isolator is approximately 18 inches tall, 3 feet in diameter, and weighs nearly 4,000 pounds (see picture).
The base isolation structural system is designed to accommodate 22 inches of horizontal building movement. Building utilities, which include mechanical, electrical, plumbing, fire protection, and low-voltage systems, are designed to move with the building. There will be a 28-inch-wide open space around the exterior of the building to allow it to move freely within this moat. Connections to adjacent buildings at each floor are covered with expansion joints to accommodate building movement within the moat.
When the LAC+USC Medical Center is completed, it will provide for 350,000 outpatients and 175,000 emergency visits per year. The base isolation system is one of many state-of-the-art technologies being installed in the new hospital. This will ensure that following a maximum credible earthquake, the new hospital will be available to serve as the hub of the County's trauma network. For more information on the status of the project, see our website at www.lacmt.org.
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