St. Croix River Crossing
- 2.2 million feet of strand installed
- Supply & installation of 160 extradosed stay cables & Gensui dampers
- Design, fabricate & commission segment lifting/transport frames
- Owner: Minnesota and Wisconsin Departments of Transportation
- Engineer: HDR
- Designer: HDR – Buckland & Taylor (COWI)
- Contractor: Lunda/Ames JV
- Subcontractor: STRUCTURAL TECHNOLOGIES
Connecting Minnesota and Wisconsin, the St. Croix River Crossing is a picturesque extradosed bridge set against the horizon. As part of a series of improvements being made to the MN 36 corridor, the structure replaced the historic Stillwater Lift Bridge. Both the Minnesota and Wisconsin Departments of Transportation were driven by the need to replace the historic predecessor given years of congestion issues and structural deterioration. To accelerate the construction of the new river crossing, the Departments elected to let the river span foundations while the design of the superstructure was being completed.
The St. Croix River Crossing combines segmental box girder and cable-stayed bridge design elements. It was chosen to aesthetically blend with the environment and be reminiscent of nature with its slender reed like columns. Spanning the federally protected waterway, the bridge provides four lanes of traffic and a path for pedestrians.
Approximately, 3,365 ft long, the extradosed section is composed of six spans. Four main spans of 600 ft, and two side spans of 335 ft and 9 inches, and 340 ft. The bridge boasts five cable stay piers with twin towers rising 60 ft above the bridge deck. Each tower supports 16 stay cables, ranging from 100 ft to 250 ft in length.
STRUCTURAL TECHNOLOGIES supported the Lunda/Ames JV by providing single-sourced supply and installation of stay cables as well as river segment lifting and walking frames. Design, fabrication and delivery of the six river segment lifting frames and two segment walkers was completed within 10 months, meeting the accelerated construction schedule.
A number of innovations were deployed to expedite the installation of the stays. Rubber-tired strand pushers with ‘slider pipes’ and horizontal ‘uncoilers’ allowed crews installed strands in 2.5-minute cycles completing a pair of stays in a 10-hour shift. A total of 160 stay cables and were installed on the project. Each stay was fitted with high damping rubber dampers to suppress cable vibrations.
When the bridge opened it was the second of its kind in the US. The St. Croix River Crossing continues to be admired not only for its improved function but also for the beauty of its form.