Slip Slidin’ Away
Better Roads Staff
• The truss is [before the move] supported on five concrete piers, three in the river and two at the east and west shorelines. Lengths of the four spans from west to east are about 245 feet, 300 feet, 300 feet and 246 feet (give or take a few inches).
• At each of the five piers, the truss is supported on two large steel bearings, with one bearing under the north side of the truss and one under the south side.
• The individual parts of the steel truss were fabricated in 1924.
• The Sellwood truss will be moved (“translated”) sideways to a new location north of the existing bridge in order to serve as a temporary detour structure while the new Sellwood Bridge is built at the present bridge location.
• At the new location, the truss will be supported on five temporary steel “bents” or piers. The contractor has installed the new bents at the same spacings as the existing concrete piers. Thus the new bents will support the truss at the same 10 bearing points (two per bent) where the concrete piers support it now.
• The entire 1,100-foot long, four-span truss will be moved sideways to its new location as a single unit. The bridge is moved in a horizontal slide, rather than a vertical pick and move.
• Due to the necessary locations of the temporary east and west approaches to the detour bridge, the final location of the truss after translation will be at a “skew” to its present alignment. The east end of the truss will be moved north about 33 feet and the west end will be moved north about 66 feet. This means that the truss will travel along a curved path as it is translated.
• The translation operation will be carried out by two contractors working together: the Slayden/Sundt Joint Venture and Omega Morgan. Omega Morgan is a subcontractor to Slayden/Sundt.
• The Slayden/Sundt Joint Venture is Construction Manager/General Contractor (CMGC) for the entire Sellwood Bridge replacement project. The joint venture consists of Slayden, an Oregon-based heavy construction contractor, and Sundt, an Arizona-based general contractor.
Translation Methods and Equipment
• Since the truss is continuous over its full 1,100-foot length, it will be important to support the truss at the 10 main bearing points (two per pier) throughout the translation operation. Otherwise the load-carrying capacity of truss members could be exceeded.
• To support the truss at all 10 bearing points during translation, the SSJV has installed steel “translation beams” from the five old concrete piers to the five new temporary steel bents. Two translation beams will be used at each pier to accommodate Omega Morgan’s skidding (or sliding) equipment. One translation beam will be positioned on either side (east and west) of the bearings that support the truss on the piers.
• Omega Morgan’s equipment will lift the truss off the concrete piers, then slide the truss along the translation beams to the steel temporary bents. Hydraulic jacks will push the truss on its journey.
• Omega Morgan will first install 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 will use their standard “skid beams.” The skid beams are 14-foot long ski-shaped steel units that slide on the Teflon pads in the track beams. Four skid beams will be 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 will sit on the track beams on the east and west sides of the bearing.
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