Once preliminary engineering was complete, crews began prepping the site and building the new bridge beside the old one on temporary fixed supports. This arrangement provided crews with ample space and access to typically hard-to-reach areas. It also increased their safety to be able to work off the roadway.
When the new bridge was finished in March 2008, it was time to put all of the planning into action. For the next step, crews closed Oregon 38 for a short time — between Friday evening rush hour and Monday morning commute time — to demolish the old bridge. Despite the reduced visibility, demolition of the old bridge had to take place at night for the replacement to meet the allotted four-day timetable. At 9 p.m. on Friday, crews began cutting away the guardrails and concrete that joined the existing bridge to the substructure. In just 12 hours, the new east-side Elk Creek Bridge was ready to begin its two-hour, 15-foot journey into its new home as part of the Umpqua Highway.
The next morning, as crews finished hauling away the concrete rubble, other teams arrived to complete the next portion of the roll.
Jacking the bridges into place is a specialized engineering feat, so ODOT and Slayden chose specialty contractor Mammoet, based on the company's outstanding reputation as rapid replacement experts. Mammoet pioneered the development and use of the hydraulic skidding systems that slide the bridge into place. Rapid replacement has been used for years in Europe and is gaining popularity in the United States.
Along with Link-Belt HC-238H cranes, Caterpillar D8 bulldozers, Komatsu PC300 excavators, and road graders, Mammoet used specially manufactured hydraulic jacks, controlled by a single operator, to move the bridge down the steel tracks to its final destination. These jacks raised and lowered the new east-side Elk Creek Bridge — two spans, 222 feet long, 38 feet wide, and weighing approximately 2.5 million pounds — with two motor-driven power packs that sit on the bridge deck. In spite of the magnitude of the project, the crew also attended to small details: For example, to protect Elk Creek against hazardous spills, nontoxic dish soap was used as lubrication for the shoes on the Teflon-coated skids that the bridge slid along.
By Saturday afternoon, the bridge roll was complete. Then work began to tie in the new bridge with the existing approaches. After the heavy lifting and sliding, plenty of hard work remained as Slayden worked quickly to replace other parts of the bridge, including abutments, precast end panels and wing walls, and final concrete paving. Crews spent the next 22 hours, while the highway was closed, securing the sides in place, double- and triple-checking measurements of the east-side bridge — a two-span, two-lane concrete structure using precast, prestressed bulb T-girders and a cast-in-place, high-performance concrete deck — to be sure the structure fit together properly and was ready for traffic.
The process went so smoothly that crews reopened the bridge nine hours earlier than expected, in plenty of time for Monday morning commuters.NOTHING SUCCEEDS LIKE SUCCESS
Later, in September 2008, crews assembled for a second time to replace the longer west-side crossing, a three-span, 320-foot-long, 38-foot-wide and 3.2-million-pound steel structure with steel-plate girders and a cast-in-place, high-performance deck. Due to the length and curve of the span, the designers opted to use steel for its lightness and flexibility.
The replacement process for the second bridge was similar to that of the first; however, because the bridge was curved, it required more complex engineering. The west-side crossing sits on a 45-degree skew, requiring careful calculations to align and attach the new span, which was designed for a gentler 30-degree angle.
One of the biggest challenges in rapid replacement is connecting the new bridge to the substructure and securing it in its final position.
The west-side bridge replacement started on a Friday evening, and by 10 p.m. Sunday the road was reopened to traffic, eight hours earlier than planned.
By selecting the design-build delivery method, valuing innovation over cost alone, and using technically difficult but effective rapid replacement, ODOT was able to keep a rural community connected and freight haulers and travelers mobile.
— Lauer is the manager of the Oregon DOT's Major Projects Branch.