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Putting the Wraps on Quakes

by Larry Cercone, P.E., Vice President of Engineering; XXsys Technologies, San Diego, CA,
James Korff, Dir. of Engrg. Services; XXsys Technologies, San Diego, CA,


Serial Information: Civil Engineering—ASCE, 1997, Vol. 67, Issue 7, Pg. 60-61


Document Type: Feature article

Abstract:

With bridges deteriorating all over the country at an alarming rate, state DOTs are searching for cost-effective retrofit solutions that will protect our aging bridge inventory from seismic jolts. An emergent composite column-wrapping technology is one solution being tried in California. Following the San Fernando earthquake in 1971, the California Department of Transportation (Caltrans) initiated significant changes in bridge design. These involved increasing minimum column ductility to assist lateral motions, providing wider seats for box girders and installing restrainers to restrict movement of adjacent spans. Most of the bridges complying with these standards survived the Northridge earthquake without any problems. The retrofits, which were to prevent bridge superstructures from falling off their supports, entailed cable and rod restrainers, shear keys, bearing replacements and catcher blocks. After the Wittier earthquake in 1987, Caltrans adopted a different approach to retrofitting. It began studying wrapping bridge columns in steel jacks to increase the shear and flexural capacities as well as to enhance ductility. After the devastation of the Loma Prieta earthquake in 1989, the column-retrofitting program was accelerated. Caltrans estimates that about 5,000 bridges in California are in need of some form of replacement or retrofit in order to meet current design practices, with a total program cost estimated at approximately $3 billion, excluding the state's 10 major toll bridges. In April 1996, Caltrans approved XXsys Technologies to use its carbon-composite system as an alternative to steel jacketing for seismic retrofit. XXsys Engineers completed the first composite contract from Caltrans in January 1997 to retrofit six columns on Interstate 5 over the San Allege Lagoon in San Diego County.

Subject Headings: Rehabilitation | Earthquakes | Bridge design | Bridges | Steel columns | Steel bridges | Seismic tests

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