Slide to the left, slide to the right and don't fall down. No, it's not a new dance, but a building with shock absorbers—a feature that could someday save more lives and property in earthquake-prone regions of the United States. Researchers at the Commerce Department's National Institute of Standards and Technology have taken the first step toward making it easier for the construction industry to include these shock absorbers, more commonly called seismic base isolation systems, in their building plans. The agency's Building and Fire Research Laboratory has developed testing guidelines for the devices that can be the basis for standards of reliability and capacity. Seismic base isolation systems, generally designed to protect structures of fewer than 10 stories from the dangerous effects of strong ground shaking, isolate a structure from the moving ground by inserting a flexible rubber layer, or teflon-steel sliding interface, at or near the structure's foundation. The interface isolates the shaking of the ground from the shaking of the structure, and minimizes damage to the structure.
Many base isolators have been used in bridges. They also have been used for fire stations, emergency command centers, liquid storage tanks and historically significant buildings. For example, the 1994 renovation of the historic U.S. Court of Appeals building in San Francisco included the installation of 256 sliding base isolation bearings.
Up until now, these devices had to be custom designed for each site and individually tested. No general testing standard existed.
"That's about to change," says BFRL structural engineer Andrew Taylor. "New testing standards, based on NIST guidelines, will provide comparable data on different systems and components and will define minimum levels of reliability and capacity. These tests will make it easier for engineers and the industry to market these devices. For the first time, the sale of "off-the-shelf" seismic base isolation systems could become a possibility."
NIST structural engineers developed the guidelines with extensive industry collaboration, as part of the BFRL's participation in the National Earthquake Hazard Reduction Program.
The guidelines can be used to conduct pre-qualification, prototype and quality control tests of elastomeric, sliding or hybrid isolation systems. They include general requirements of the test facility, instrumentation, calibration, data acquisition, data analysis and reporting of results. The American Society of Civil Engineers is currently reviewing the guidelines. ASCE approval of testing standards for seismic base isolation systems, based on the NIST guidelines, is expected by the end of the year.
For technical information, contact Andrew W. Taylor, Rm. B158 Building Research Bldg., NIST, Gaithersburg, Md. 20899-0001, (301) 975-6078, e-mail: andrew.taylor [at] nist.gov.
A non-regulatory agency of the Commerce Department's Technology Administration, NIST promotes U.S. economic growth by working with industry to develop and apply technology, measurements and standards.