BURLINGTON — As contractors worked on pilings that will eventually support the permanent replacement span for the Skagit River Bridge, state transportation officials at riverside Wednesday discussed details of the next construction project, which will raise the height clearance on the bridge.
The bridge on Interstate 5 was struck May 23 by an overheight load. While the bridge structure is 18 feet high at its center, the sloping arches of the portal frames dip towards the edges as low as 15 feet 6 inches at the fog line — the white line on the right side of the road. Over the years, the Skagit River Bridge has been struck regularly by trucks.
The May collision sent one span of the steel truss bridge into the Skagit River, along with three people. They suffered no serious injuries.
Almost immediately, state Department of Transportation officials sought a way to change the configuration of the bridge to prevent future strikes. They submitted a plan to the Federal Highway Administration and got funding.
“Obviously with what happened here it emphasized the fact that there is a risk when we have oversized vehicles using this route. We know there’s going to continue to be more oversized loads that use this route,” said DOT Assistant Regional Administrator Jay Drye. “Freight is only going to continue to increase with time.”
The collision required all of the I-5 traffic, which averaged about 71,000 trips per day, to detour onto local roads for about a month. Local businesses say the subsequent gridlock led to massive retail losses.
The next closures, planned for only nighttime hours, will have minimal impact on local businesses, said Linda Fergusson, president and CEO of the Burlington Chamber of Commerce.
DOT’s Drye said the highway agency will pay the full cost of the retrofit work, under the same emergency relief fund used to pay for the permanent span replacement.
The cost of the contract is estimated to be between $2.5 million and $3 million. The state also plans to replace about 1,500 rivets on the bridge. Removing that many rivets will not impact the bridge’s structural integrity, DOT traffic engineer Dina Swires said Tuesday.
Drye said the bridge has more than 50,000 rivets on the structure underneath the deck. With contract management, engineering, sales taxes to Burlington and Mount Vernon, and contingencies, total cost of the project is expected to be around $4.5 million, Drye said.
A visible change will be a more rectangular shape instead of the current arch with variable clearance. Originally the arched design of the bridge was an aesthetic component, said Todd Harrison, state Department of Transportation interim state bridge and structures engineer.
“A lot of those bridges built in the ’50s had to do with architectural features and fabrications,” Harrison said. “It’s prettier with the arch but less risk straight across.”
Bridge closures to replace the beams will happen only at night. Sometimes the bridge will be closed in both directions. Other times it will be closed to one-way traffic. The bridge’s structural integrity will not be compromised by replacing the components, Harrison said.
“There won’t be any weight restrictions on the bridge,” Harrison said. “They will do one frame section at a time, cut it out and bolt it in.”
The center beam — a critical, load-bearing component — will remain intact, he said.
The work should be done “well ahead of the holiday shopping season,” Harrison said. DOT says the contractor, which has not been selected, could be done by Nov. 23.
The DOT has planned seven 12-hour closures and 36 eight-hour closures, all of which will happen at night. If the contractor can use fewer closures, they will be paid an incentive.
Of the 14 steel truss bridges on Interstate 5, the Skagit River Bridge is the lowest of them all.
“Any bridge is at risk of being hit,” Harrison said. “This bridge was hit because the overheight load was in the wrong lane.”
The DOT and the Federal Highway Administration are pursuing legal action against Mullen Trucking for the cost of the replacement span, Drye said.
Read more about the bridge’s collapse at http://skagit.ws/bridgecollapse.