The road between 92nd Street KPN and the Key Peninsula Civic Center will be closed to traffic beginning Aug. 10 to allow for the crews to begin work on the Vaughn Bay bridge. The road will be closed through April 2010.

A 2.2-mile detour will divert traffic around the construction zone via Olsen Road KPN and 92nd Street.

The new bridge will be a 219-foot, single span, concrete girder structure with two 12-foot lanes and 6-foot shoulders. Storm water treatment embankments will also be installed at several locations to treat road runoff.

The existing 5-span concrete bridge was built in 1966. In 2002, Pierce County Public Works and Utilities engineers determined that the bridge is vulnerable to earthquakes due to its simple spans-and-supports construction. The bridge beams are not restrained against movement, and the beam supports are not big enough to accommodate such movement.

In the event of a major earthquake or even a minor quake in the wrong direction, the bridge beams could slip off their supports, causing the bridge to collapse.

The bridge appeared to be in good condition otherwise, and the engineers’ first thought was to seismically retrofit the structure. But upon closer inspection, they discovered fairly extensive cracks that penetrated the thickness of the concrete bridge deck, as well as reinforcing steel that was also showing signs of degradation.

The only way to correct the problems is to replace the structure, so in 2003 the county began securing funds for bridge replacement. The single span design of the replacement bridge will meet current seismic standards.

“As we all know, this is a time when budgets are strained and money is tight,” said Field Engineering Manager Jerry Bryant. “We need to ensure that the projects we pursue and the money we spend provides the greatest possible value to Pierce County taxpayers.”

Replacing the bridge will cost more than a retrofit, but it avoids having to spend money for retrofitting that will be removed later when the bridge is replaced. “We have to make the bridge safer,” Bryant said. “But we don’t have to spend twice as much money to do it.”

Nearly all of $2.86 million project cost will be covered by a Federal Bridge Replacement Fund grant administered by the Federal Highway Administration. The remaining $137,000 will come from the county road fund.

The old bridge will be removed and the new one constructed in accordance with all applicable environmental regulations and requirements, which include very specific limitations as to when and how the work may proceed. The project will offer measurable environmental benefits by removing 36 concrete pilings that affect hydrology, debris and sediment flow at the mouth of Vaughn Creek. In addition, embankments constructed with the new bridge will treat the majority of storm water runoff.

Scarsella Brothers, Inc. of Seattle is the construction contractor.

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