December 24, 2001
Aging structure deteriorating rapidly
by Lisa Allen
Valley View Editor
DUVALL-Barely a year after the new Novelty Bridge was opened to traffic, Duvall residents are being told to brace for the impact of yet another extended bridge closure.
The Woodinville-Duvall Bridge will be closed from June 24 through Sept. 30, 2002, for needed repair, King County Road Services has announced.
Approximately 17,000 vehicles a day cross the bridge, which was constructed in 1951.
"The bridge was designed for 27-ton vehicles," Project Engineer Ken Wilson told the City Council at their Dec. 13 meeting. "Nowadays, the average truck weight is 36 tons. That's 33 percent heavier a significant increase for a bridge designed for much smaller loads."
Wilson noted that repairs will stiffen the structure.
"You can feel the vibrations on the bridge now," he said. "We have seen increased cracking. The whole structure is degrading. It will be inconvenient but there are so many problems the bridge has to be closed."
A 20-ton load limit was placed on the bridge July 3 after engineers discovered the superstructure of the bridge cracking under the heavy weight of the numerous heavy trucks that traveled it daily. Engineers enforced the load limits to prevent further damage to the deteriorating structure until the planned repairs are completed. The bridge was closed for one day on June 30 so workers could repair expansion joint and rail sections and conduct further inspections.
Wilson said inspections have revealed cracking at girders and the overhang and shear cracks on the girders, as well as sidewalk soffit cracks. He noted the three most significant weaknesses are cracking, inadequate top reinforcing cover and damage at the joints, but added that seismic vulnerability is also a factor.
"A year and a half ago, we didn't contemplate this," he said, "But with tighter scrutiny on the Woodinville-Duvall Bridge, the less we liked what we saw. We posted the load restrictions which we were required to do legally, and that allowed us to keep the bridge in operation."
Wilson said the project goals are to improve the bridge load capacity and overlay the bridge deck, adding that summer weather is necessary to complete the job in three months, plus the county wanted to wait until the end of the school year before closing the bridge.
"We need to assure continued community mobility, maintain the bridge useful life and improve the public safety," he emphasized.
On the timeline of activities, he said, workers will first replace the anchor bolts on the approach span from below, then close the bridge, remove the existing rail, replace the main span anchors from below, scarify the deck, drill and install hanger bar hardware, install deck steel and modified concrete overlay, install new curbs and rails and finally reopen the bridge, at which time the posted load limit will be removed.
The total cost is expected to be $2.5 million, he said.
Jim Markus, King County supervising engineer, said that engineers cannot predict the useful life of the repaired bridge, but expect the improvements will give it another 20 to 25 years.
"The Woodinville-Duvall Bridge is the longest bridge in King County inventory," he said. "It cost $12 million for the Novelty Bridge replacement and I would guess it would take $25 million to replace the Woodinville-Duvall Bridge."
Traffic engineer Norton Posey said engineers considered the possibility of increasing vehicle capacity while repairs are made, but concluded that it was unfeasible.
"We considered adding a right-turn lane for vehicles turning south off the bridge," he said. "But it would only add capacity of four more cars and cost an enormous amount."
Posey said the county will be informing the public of detour routes and traffic mitigation.
"We probably won't have an open house," he said. "We are thinking more of a targeted presentation, maybe to the Chamber of Commerce, for folks who wish to hear about it."
He said the library will have a display, brochures will be available in April and postcards will be mailed to all affected residents just before the closure. Information can also be accessed at the county's Duvall bridge Website at www.metrokc.gov/kcdot/roads/projects/duvallbrdg/dvllbrdg.htm.
The aim of the traffic engineers is to reduce commuter impacts, Posey pointed out. He said consideration had been given to a one-lane closure for five months, but that studies determined that the closing of the eastbound lane for five months would have the same impact as total closure for three months.
"So we recommended closure for three months ‹ get in, get it done and get out," he said. "We will look at existing traffic demands to develop a base line, do a model distribution of trips and figure out what intersections will be impacted and the mitigation needed."
Detour routes will be N.E. 124th, High Bridge and SR-203. He said flagging will occur during peak hours at SR-203 and 12th and SR-203 and 203 St S.E. (Crescent Lake Road), using a uniformed officer, noting that the cost of a signal at those intersections would be $250,000 for each intersection as opposed to $10,000 for a flagger.
At the new signal on N.E. 124th and W. Snoqualmie Valley Road, a video camera will aid technicians in timing of the lights.
"Technicians can see the traffic and make changes in timing adjustment as needed," he said.
Marcus said King County will offer the contractor an incentive to finish early, similar to what was done with the Novelty Bridge, "however, there is not as much leeway, but it does encourage them to solve problems the day they come up. There will also be penalty fees. We figure it will cost $30,000 a day in inconvenience for the public, at 17,000 cars per day. There were a load of problems on the Novelty Bridge but they all got worked through because we had a responsible bidder."
Business owners at the meeting expressed their concerns over the summer closure because of the tourism factor, but Marcus said the economic impact can't really be calculated and that the permit will require the work be done in the summer because of the extended light.
"People can still get to Duvall," he said.