A damaged Duwamish River bridge in Tukwila, hit by a tall truckload last week, will be repaired and reopened in four to six weeks, the city announced Tuesday.
A specialty contractor called Flame On Inc., based in Monroe, Snohomish County, will use a technique called heat straightening, or flame-straightening, to restore an overhead beam and two side beams to their correct positions. Heat is applied to precise locations, at up to 1,200 degrees, with a welding torch along the path where impacts from the truck stretched the steel, explained Tyler Thomas, company vice president.
“We’re just shrinking where it got stretched,” he said. Restraining chains are applied to prevent the beam from expanding while heating, and then the cooling-off phase restores the former shape, he said.
Repairs are weather dependent, and for now the bridge on 42nd Avenue South remains off-limits to traffic, said the announcement by Tukwila City Administrator David Cline.
None of the steel on the truss bridge, built in 1949, was sheared or separated, according to an inspection last week by a King County bridge team. The hardest-hit part is an overhead sway brace, shoved 18 inches ahead by the northbound cargo.
That impact yanked an attached, weight-supporting vertical beam 10 inches inward toward the northbound lane, an inspection report says. Portions of another vertical beam were bent by falling cargo on the southbound side.
Flame On’s contract with Tukwila says the firm needs five to seven days. Repair teams can work in cold but not in heavy rain, which would cause too-rapid cooling and make the steel brittle, said Thomas. Among projects nationwide, he said the most similar to Tukwila is a Nooksack River bridge near Bellingham, where some oil refinery equipment banged multiple beams.
Tukwila Mayor Allan Ekberg signed an emergency proclamation to accelerate repair work. The estimated cost is $221,000.
The city’s four- to six-week estimate takes into account rain, snow and holidays, plus two weeks for post-repair structural calculations and inspections, Cline said.
City staff say they are seeking to bill the truck driver’s insurance. The semi and its load, consisting of an open-sided yellow container and heavy cables, belong to Sunset Machinery in nearby Skyway, the firm’s owner has said.
Already, the bridge was under load restrictions and a 15 mph truck speed limit, because past inspections found it structurally deficient. The bridge serves 3,000 trucks and 7,000 other vehicles daily.
Tukwila is moving forward toward full design to build a replacement bridge by 2025 in the same location and has already secured $13.5 million, or roughly half the cost.
That strategy is opposed by a neighborhood group, Allentown Advocates, some of whom have wanted the trucks moved elsewhere for three decades. Neighbors suggest building the new bridge near an Interstate 5 truck stop farther south; or building both a car bridge at 42nd and a second truck-only bridge near 48th Avenue South, directly into a BNSF Railway freight yard.
Sally Blake, the group’s co-founder, said she welcomes the temporary respite from 3,000 truckloads crossing the bridge, then a small arterial between Tukwila Community Center and houses.
“It’s been very nice; the kids are safer walking to the community center. People are congregating on the bridge. There are no diesel fumes,” she said.
On the other hand, the main truck detour follows a steep timber-supported bridge across I-5, between Skyway and Tukwila, that’s difficult to find. Tukwila plans to study long-term options, including new surface truck roads.