A Knoxville, Tenn., bridge is getting earthquake protection as it is rebuilt.
The Henley Bridge over Fort Loudoun Lake was closed in January 2011 for a major reconstruction project. The decking and upper structure are being replaced on top of the existing piers and arches, which were sound.
The Knoxville News Sentinel reported part of the project includes devices designed to mitigate the shaking of an earthquake.
“It’s actually a damper, like the shock absorber on your car,” said Wayne Seger, structures director for the Tennessee Department of Transportation. “It takes the zip out of the movement.”
The dampers, called lock-up devices, will be installed on “super piers” that go down to bedrock on both ends of the bridge. Ten of the dampers will be installed at each end of the 1,793-foot-long bridge.
Crews had to drill 103 feet to reach bedrock on the downtown end of the bridge. They found bedrock at half that depth on the opposite end.
Each device costs $10,000, according to TDOT regional spokesman Mark Nagi.
Dampers have been built into bridges for decades, but Seger said the type being used on the Henley Bridge project has not been used before in Tennessee. He said similar devices have helped bridges in California and outside the U.S. endure earthquakes.
TDOT project manager Kristin Qualls said as of March 26, 53.2 percent of the construction time has passed and 37.5 percent of the work is finished. The measurement is by materials used in rebuilding the structure, not measured on work performed.
The original bridge was completed in 1931.
The $24.7 million reconstruction project is scheduled to be completed in June 2013, but there is an early incentive. TDOT built into its contract with Britton Bridge LLC, a bonus of up to $1 million if work is finished by Dec. 31.
The completed bridge will have two 12-foot-wide driving lanes in both directions and a center turn lane for the 38,813 vehicles a day traveling on it. It will also feature bicycle lanes and wider pedestrian sidewalks.
The bridge will carry U.S. 441 over the lake, which is a section of the Tennessee River.
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