American Crane & Transport
About the Sellwood Bridge
The 87-year-old Sellwood Bridge replaced a ferry called the John F. Caples. The steam-powered ferry took an average of 582 vehicles and 482 pedestrians across the Willamette River every day, compared to the 30,000 vehicles that crossed the bridge in 2012.
The Sellwood was Portland’s first fixed-span bridge, which means it was the first bridge in the city that did not have a draw or swing span. In 1960, the Sellwood Bridge underwent extensive repair to prevent it from collapsing after settling issues caused cracked concrete.
However, through the years the aging bridge became more deficient. Among the bridge deficiencies that hastened the decision to replace it were that it could not handle the volume of traffic; had a rating of two out of 100 on the bridge efficiency scale; buses and heavy trucks were restricted from using the bridge; it has narrow lanes and sidewalks and no shoulders; it has no bike facilities and poor connections to a trail system; and it was not designed to withstand earthquakes, even though the area is in one of the most dangerous earthquake zones in the country.
In one of the longest bridge moves ever made, crews from Omega Morgan strategically moved the Sellwood Bridge in Portland, OR from its permanent concrete supports to temporary steel piers to make way for a new bridge to be constructed across the Willamette River.
The 12-hour move, which was watched by hundreds of onlookers all day on Saturday, January 19, was the result of months of planning and precise execution. The Sellwood Bridge, at 1,972 feet long, 75 feet high and, 28 feet wide, is among the state’s busiest bridges with 30,000 vehicle crossings each day.
Once it was secured into place by late January, the old bridge in its new location would become a temporary route while the new $307.5 million bridge is built in the original location. The new bridge will open in 2016.
“We are really pleased to be involved in this highly important, complex and exciting project,” said John McCalla, Omega Morgan’s CEO/president.
The job was complicated by the fact that it was not a straight-across move. Instead, the east end of the bridge needed to be moved only 33 feet while the west end had to be moved 66 feet.
Both Omega Morgan and Slayden/Sundt Joint Venture have successfully used this detour bridge method on other projects, according to the company.
“Omega Morgan has moved bridges weighing upwards of 8 million pounds, but this one [did] offer some additional challenges,” McCalla said.
Devising a strategy to move the bridge in one piece helped Omega Morgan win the contract after showing that it would save time, money and duplication of efforts, according to parties involved in the project. Other proposals had suggested expensive and redundant structural features and extensive staging.
The plan involved sliding the aging bridge on skid gear to the north of the existing bridge and then mounting it on new piers that had been built in the river. The bridge would then become the “shoofly,” or detour, while construction begins on the new bridge.
Engineers used 10 sliding jacks, 40 lifting jacks and a central control system to make sure the move progressed as planned. The truss span was designed as a continuous structure rather than a series of connected spans, which is unusual. This design required the contractor to move the entire span in one piece.
In preparation for the move, crews removed short spans at the east and west ends of the truss span that would not be part of the new detour bridge. Hydraulic jacks lifted the truss span several inches off the old concrete piers, and then horizontal jacks pushed it on rails along steel translation beams linking the old piers with the detour bridge piers.
The Multnomah County Board of Commissioners approved the rigging method in June 2012 after learning about the advantages of this strategy proposed by Omega Morgan. According to Larry Gescher, construction manager for general contractor Slayden/Sundt Joint Venture, advantages of this method included savings of $5 to 10 million over other methods proposed; allowed for the new bridge to be built in one phase; saved a year in construction time; the temporary detour structure is as strong if not stronger than the existing Sellwood Bridge (including seismically); and there is no need for redundant structural features on the new bridge. As well, because drivers are using the temporary bridge, they will be separated from construction workers, ensuring a safer work environment.
Prior to the bridge move, temporary approach spans were installed at the west and east ends of the relocated bridge to link Highway 43 in southwest Portland to S.E. Tacoma Street. These will remain in place throughout construction of the new bridge.
The bridge move started early on a foggy Saturday morning, moving at a snail’s pace of about six feet per hour. About 35 crew members remained on the bridge throughout the move, operating the network of 50 hydraulic jacks and that lifted and pushed the bridge on ramps to its new location and monitoring the truss.
According to The Oregonian newspaper, engineers had calculated that the structure could tolerate about four inches of bend. The routine was to push the bridge a couple of inches and then stop to assess the progress. Using survey laser targets, 10 GPS sensors, 30 stress-strain gauges, 10 smarts of levels and the review of 35 staff members, the newspaper said the process was well monitored.
One of the complications of the move was that the new interchange at the west end is larger than the older one. To provide for the extra space, the bridge had to move in a skewing motion to compensate.Rigging Review
- Omega Morgan’s equipment lifted the bridge truss off the concrete piers and then slid it along the translation beams to the steel temporary bents. Hydraulic jacks pushed the truss on its journey. Omega Morgan uses this same equipment regularly for operations such as moving newly-built barges around the fabrication yard at Port of Portland and loading/unloading container cranes on/off barges at many ports around the United States. Some of the same equipment was used to load the arch span for the Sauvie Island Bridge onto a barge in 2007 in preparation for setting the span in place at the bridge site.
- To prepare for the truss-sliding operation, Omega Morgan installed U-shaped track beams on top of the translation beams from the concrete piers to the steel bents. Teflon pads are glued to the track beams to provide slick sliding surfaces.
- To actually lift and slide the bridge truss, Omega Morgan used their standard skid beams, which are 14-foot long, ski-shaped steel units that slide on the Teflon pads in the track beams. Four skid beams were used at each of the concrete piers, with two of the skid beams located at the north side bridge bearing and two at the south side bearing. At each bridge bearing, the two skid beams sat on the track beams on the east and west sides of the bearing.
- For the Sellwood operation, each skid beam had two vertically-oriented 150-ton capacity hydraulic jacks for lifting the truss off the concrete piers and lowering it onto the temporary steel bents. With two skid beams at each bearing, this meant that four jacks lifted the truss at each bearing. Since there were 10 bearings in total (two per pier), Omega Morgan used 40 jacks to lift the truss. At each of the three river piers, the weight of the truss (including the concrete roadway deck) was about 900 tons. At each of the end piers, the bridge weight was about 340 tons. The total weight of the truss span was estimated to be about 3,400 tons.
- In preparation for the lifting and translation operations, the general contractor installed custom-designed steel cradles at each truss bearing (10 cradles total). The purpose of the cradle at each bearing was to carry the weight of the truss from the bearing to the four lifting jacks.
- To move the skid beams and truss along the track beams, Omega Morgan used 10 horizontally-oriented 75-ton capacity hydraulic jacks to push on the south side skid beams. The north skid beams and south skid beams were tied together to assure that they moved together. In Omega Morgan’s system, the pushing jacks were pinned to the rear ends of the skid beams and pushed against clips on the sides on the track beams. Due to the slick surface provided by the Teflon pads in the track beams, only a small part of the pushing jack capacity was needed to move the truss. The pushing jacks could also be used to pull back in case a skid beam moved too far.