Base Isolation in the United States

Many people in the United States believe that the buildings in which they work are built on rollers" to make them safe in earthquakes. Not only are base-isolated buildings not constructed on rollers," but, unfortunately for most occupants, their buildings are not base-isolated. Implementation of base-isolation technology in buildings was first introduced to the United States only about 10 years ago. Although several hundred bridges have been base-isolated, fewer than 20 U.S. buildings currently have benefit of this technology.

The first application of base isolation in the United States was to seismically retrofit the City Hall building in Salt Lake City, a historic landmark structure of unreinforced masonry. In retrofitting that building, it was determined that base isolation could improve the building's safety without significantly disrupting the historic fabric of the structure, unlike conventional strengthening approaches in many cases.

Because such preservation is a fundamental consideration in retrofitting historic structures, many of the base-isolated buildings in the United States today, either completed or under construction, are monumental public buildings. These include City Hall buildings in the California cities of Oakland, San Francisco, and Los Angeles; the U.S. Seventh Circuit Court of Appeals building in San Francisco; and the School of Mines building at the University of Nevada.

In addition, because base isolation greatly enhances post-earthquake building operation and reduces nonstructural and contents damage, several new hospitals in the Los Angeles area and a few new municipal Emergency Operations Center buildings were constructed using this technology. It can be expected that many more buildings will benefit from this approach in the future.