Big, heavy, Oregon bridge makes an innovative move

By John Latta, jlatta@randallreilly.com

You jack it up, you slide it. Simple.

But the Sellwood Bridge is not small. It is 1,100 feet long (a continuous structure) and 3,400 tons.

The two-lane Oregon bridge was jacked up (just a few inches) and then slid or skidded (at an angle) into a new position. It may just be the longest bridge span ever relocated this way. And because of the move there will be a bridge for traffic to cross the wild Willamette River while a new bridge is built alongside, instead of having to take a long alternative route.

The move saves Multnomah County millions of dollars by shaving up to a year of construction time and saving drivers a long detour. The proposal was to save the original span by moving it to the side, reopening it to traffic and leaving room at the original site for construction of a new $307.5 million bridge that will be completed in 2016.

The moving work was done by Portland-based Omega Morgan, which says its plan was the only one that did not require destruction of the old (1924) bridge that would have required 30,500 vehicles a day to re-route miles away to other bridges. And, says the company, there were other benefits to the plan including reducing environmental impact and improving safety for bridge users and workers.

The continuous Sellwood Bridge span bridge rests on its new steel piers after the move.

Multnomah County encompasses the most populous area in Oregon, including the city of Portland and the heavily travelled Sellwood Bridge. The project was one of the largest the county has undertaken in decades, according to officials managing the project. The county say that “considering the rarity of four-span bridges, the Sellwood move could be the first time such an operation has been performed for a structure of this type. This is,” says the county, “one of the longest, oldest structures to be moved in this way.”

Omega Morgan assigned a team led by Vice President of Engineering Ralph Di Caprio, whose experience in executing complicated moves includes the removal of Portland’s Sauvie Island Bridge and installation of the new bridge, managing the Third Avenue Bridge project in New York City, moving two 900-ton spans on the Hood Canal Bridge and the transport and launch of the Kalama River Bridge.

The move took 12 hours

The crew raised the truss span vertically by several inches and then pushed it north by hydraulic jack-and-slide beams. It was then slowly moved twice as far on the west end (66 feet) than at the east end (33 feet) to accommodate for the new, permanent bridge being wider at the west end, flaring from two to four lanes to add traffic capacity. The truss span was then moved on a radius, along a curving path, adding to the complexity of the execution.

Multnomah County’s fact sheet for the ‘Sellwood Bridge detour structure and truss translation’ reveals the complexity of the job.

The heavy work had its lighter side. A common dishwashing soap was used to lubricate pads on the slides.

Multnomah County’s fact sheet for the ‘Sellwood Bridge detour structure and truss translation’ reveals the complexity of the job.

• The actual length on the continuous steel truss between end bearing points is 1,091 feet and 2-1/4 inches; adding the overhang past the bearings makes it about 1100 feet long overall.

• The steel structure consists of four spans between support piers but is continuous over the entire 1,100-foot length with no hinges or expansion joints. Four-span continuous trusses are exceedingly rare. We’re aware of only a couple of others in the United States.

Special jacking and sliding equipment was needed to “skid” this long, heavy and old bridge sideways to temporary new piers.