New bridge for a new age

Graphics by Mark Boswell, Eddie Thomas, Ray Grumney and Jim Foster • Star Tribune

WIS.

Houlton

Stillwater
Lift Bridge

36

Stillwater

St. Croix
River
Bridge

MINN.

Oak Park
Heights

Reaching a mile long and dwarfing its 1931 predecessor, the Stillwater Lift Bridge, the new St. Croix River bridge represents compromises by 28 'stakeholders' who forged an agreement after years of debate. Its rare design makes it only the second major bridge of its kind in the United States. The four-lane bridge, standing 10 stories above the St. Croix and 2 miles south of the Lift Bridge, was built sparingly to avoid overwhelming the scenic view.

Two bridge styles in one

Engineers designed an ‘extradosed’ style to make the bridge more compatible with the St. Croix, a protected ‘wild and scenic’ river. It combines cable-stayed and box-girder styles. Towers were designed to stay below the Wisconsin bluffline.

Cable-stay style

Each cable supports the bridge with 76 plastic-coated steel strands bunched together inside a pipe. These cables are shorter than usual to make the bridge appear sleeker.

Box-girder style

Each girder is a hollow box that gives support without added weight. They are more shallow than a usual box-girder bridge.

Piece by piece

Individual box girder segments were brought in by barge, lifted into place and attached using epoxy and steel cables. In total, 988 segments make up the bridge’s surface.

Pier design

To boaters, piers look ‘open’ to make them feel smaller. Engineers reduced the number of two-pier sets standing in the river from six to five to further reduce the bridge’s presence.

Cable-stay style bridge

Box-girder style bridge

Comparing new bridge to others nearby

Constructing the bridge

650

Pre-cast bridge segments that were barged to the construction site from Grey Cloud Island casting yard in Cottage Grove.

330

Pre-cast at bridge location and some poured-in-place segments that were used on the bridge approaches.

180 tons

Average weight of a typical precast bridge segment.

563.8M lbs.

Total weight of the con-crete used in the construction of the bridge.

42.3M lbs.

Total weight of the steel used in the construction of the bridge.

5.2 miles

Length of the visible stay cables (They contain about 400 miles of cable strands).

20,947 cubic yards

Concrete poured during the pier foundation work, that’s about 2095 concrete trucks.

1,969 miles

Length of all the cable strand in the bridge that are not visible. That’s about the round-trip distance of Stillwater to Dallas, Texas.

988

Number box girder segments make up the bridge’s surface.

Sources: Minnesota Department of Transportation, Sensible Bridge Partnership

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