Teflon Trick Makes Bridge Move Quick
A sticky situation found a slick solution when engineers in Oregon decided to move a 3,400-ton, one-piece bridge by sliding it along tracks covered in Teflon and liquid dish soap.
The 87-year-old Sellwood Bridge had to be moved to a new location to serve as a temporary detour while its replacement was being built. The new bridge is scheduled to open in the summer of 2015.
But moving an 1,100-foot-long continuous four-span steel structure with no hinges or expansion joints had engineers at the Oregon Department of Transportation scratching their heads.
So they turned to Teflon (and a lot of heavy equipment).
A 'Highly Unusual' Undertaking
The entire 3,400-ton bridge was moved sideways as one entire piece to its new location on Jan. 19, 2013, making it one of the largest bridge parts ever moved. The move was done in a horizontal slide, versus a vertical pick-and-move.
Although the move only took 14 hours, the bridge was closed for a week to install road connections and complete an in-depth inspection.
"While translation of shorter bridges is quite common, it is highly unusual to translate a multi-span bridge of this length in one piece," Ed Wortman, Multnomah County engineer, explained on the project's website.
"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. Similar comparisons have been difficult to find," said Wortman.
The east end of the bridge was moved north about 33 feet, and the west end was moved north about 66 feet, so the entire bridge had to travel along a curved path.
At its new location, the bridge is being supported on five temporary piers, or "bents," that were installed at the same spacings as the existing concrete piers and support the structure at its 10 main bearing points. Steel "translation beams" were used to support the truss at all 10 bearing points during the move.
A Teflon-Tough Move
The truss was lifted off the concrete piers, then slid along the translation beams to the temporary steel bents with the help of hydraulic lifts.
First, U-shaped track beams were placed on top of the translations beams. Teflon pads were glued to the track beams and doused with liquid dish soap to make a slippery surface, Equipment World reported. Ski-shaped, 14-foot-long steel skid beams slid on the Teflon pads in the track beams.
Forty vertically oriented hydraulic jacks, each with 150-ton capacity, lifted the truss off the concrete piers and lowered it back on to the temporary steel piers. To slide the skid beams and truss along the track beams, 10 horizontally oriented 75-ton capacity hydraulic jacks were used to push on the south side of the skid beams.
The north and south skid beams were tied together to make sure they moved simultaneously. Thanks to the slick Teflon surface, only a small amount of pushing power was necessary. Since the angle of the move required the west end of the truss to be moved twice as far as the east end, the pushing jacks were controlled so that they pushed twice as fast on the west end.
Skid beams were coated in Teflon, enabling hydraulic jacks to easily push the entire Sellwood Bridge to its new location.
Since any excessive twisting or bending could have damaged the truss, an engineering team analyzed the bridge's tolerance limits before the move and periodically checked any movement during the move.
After the move, a team of experienced bridge inspectors inspected the bridge to make sure no damage occurred before reopening the bridge to the public.
Two contractors worked together to pull off the move: Slayden/Sundt Joint Venture, the construction manager and general contractor for the entire bridge replacement project; and Omega Morgan, a subcontractor involved in transporting and handling heavy equipment and structures.