Building Sturgeon Bay's New Bridge

Story by Mike Larson, Editor. | September 28, 2010

The new $29.9-million, two-lane, rolling-leaf bascule bridge being built across the Sturgeon Bay Ship Canal in downtown Sturgeon Bay, Wis., is cruising along right on schedule and is expected to be completed by its end-of-September deadline.

The new bridge, named the Maple to Oregon Street Bridge, is being built to boost traffic capacity through downtown Sturgeon Bay, a popular summer destination that's the gateway to Door County, which sees about 2 million tourists each year.

An overall view of the bridge shows the fixed piers and decks leading to the two larger piers that support the raiseable sections. The existing bridge is visible in the background.

The new concrete bridge will complement the 75-year-old, two-lane, steel-truss Michigan Street Bridge, which crosses the canal a few hundred yards to the west and is a local landmark registered on Wisconsin's list of historic places. Current plans call for it to be rehabilitated sometime in the future.

In addition to providing more traffic volume, the new Maple to Oregon Street Bridge will also carry trucks too heavy for the existing bridge's 5-ton weight limit.

Together, the two bridges will provide four lanes of traffic capacity over the Sturgeon Bay Ship Canal, which cuts across the Door Peninsula, connecting the bay of Green Bay with Lake Michigan.

This vital waterway not only carries recreational powerboats and sailboats; it also forms a key route for gargantuan freighters up to 1,000 feet long that sail year-round to a major shipyard in Sturgeon Bay for maintenance and repair.

Keeping the canal open for large freighters was a major consideration both in designing the new bridge and planning its construction.

New Bridge Meets Needs Of Vehicles And Vessels

Owned by the Wisconsin Department of Transportation (WisDOT), the Maple to Oregon Street Bridge stands 1,055 feet long, 48 feet wide, and offers up to 24 feet of clearance above the water.

Its 10 poured-concrete piers support nine spans.

The opening span is formed by two 154-foot-long bascule (movable) sections that meet in the middle and can be raised to let ships pass between.

With bascules raised, the bridge offers an opening 200 feet wide between its main piers — plenty of space for even the widest freighters.

All of the bridge's other spans are stationary, each formed by five pre-stressed, pre-cast concrete I-girders supporting a poured concrete deck. The girders measure 54 inches deep and 95 feet long. The deck carries two lanes of traffic, two bicycle lanes and two sidewalks.

The new bridge was designed by Teng & Associates, Inc., Chicago, which is also providing on-site engineering support and construction inspection.

Lunda Construction Co., Black River Falls, Wis., is the general contractor building the bridge, and was also subcontracted to build the approaches that connect each end of the bridge to local streets.

Common Construction, Unique Challenges

Construction began in October 2006, with completion scheduled for Sept. 30, 2008.

Setting one of the pre-cast, pre-stressed girders that support the bridge deck. Photo courtesy of Teng Engineering.

The fast-track schedule demands precise coordination between Lunda, its subcontractors and the U.S. Coast Guard, to be sure construction stays on pace without hampering the arrival or departure of freighters sailing the canal.

The construction techniques on the project are common for a bridge of this type, according to both Lunda project superintendent Dave Sweere and Teng project manager Rich Jarmakowicz.

Says Sweere, "The construction process on this job is pretty typical. You drive pilings into the river bottom, pour concrete piers atop the pilings, and then build the deck on top of the piers."

"Some of the most creative solutions," Sweere says, "have come in finding ways to keep the project moving while meeting our commitments to others who have a stake in this waterway, like the DNR and Coast Guard."

"For example," he relates, "the Wisconsin Department of Natural Resources (DNR) was originally concerned that driving pile in the canal from March through June of last year might disturb spawning fish. To be sure it wouldn't, we took underwater video as we drove the first pilings. After carefully analyzing the video, the DNR let us work through those four months. That kind of cooperation has helped keep us on schedule and relationships good between everyone involved."

In another example, Lunda clears the timing of its larger lifts and in-channel work with the U.S. Coast Guard and with Bay Shipbuilding Co., just to be sure no vessels will need to use the canal while the work is going on.

Building From The Bottom, Up

Each of the 90-ton-capacity steel H-piles that support the piers was driven until its bottom rested on bedrock about 35 feet to 40 feet below the river bed. About 35 piles support each of the eight standard piers.

The two large piers that support the moving spans each sit on110 piles.

After driving the piles for a pier, Lunda formed and dewatered a sheet-pile cofferdam around them, and poured a 15-foot-thick concrete sealing slab on the river bed, followed by an 8-foot-thick footing, and the rest of the vertical pier.

Each of the eight approach piers measures 3-1/2 feet thick, 48 feet wide, and contains about 250 cubic yards of concrete.

The two large piers that support the movable bridge sections each contain 3,000 cubic yards of concrete.

All of the concrete is being supplied by Premier Concrete, Sturgeon Bay.

To get concrete to the piers, Lunda laid an underwater welded-steel pipeline from the on-shore pumping station to the pier construction site. The pipeline reached horizontally along the canal bottom until it reached the cofferdam, then rose vertically up and over the cofferdam wall. According to Lunda's Sweere, the system used up to 850 feet of horizontal pipe to reach the farthest piers.

A superplasticizer was added to the concrete to help it flow for easier placement.

Deck Features Stationary And Moving Sections

Each of the eight stationary deck sections spanning the piers consists of the five previously described girders topped by a poured-concrete deck. An interesting feature of the deck is its many widened areas designed to enable people to relax and watch activity along the canal.

The 308-foot-long span that can be opened to accommodate ship traffic is formed by the two 154-foot moving sections, which meet in mid span.

Each of the moving sections consists of a steel frame supporting a 7-inch-thick poured-concrete deck. The deck uses a special lightweight-yet-strong concrete mix that reduces each section's weight by more than 42 tons, compared to using standard concrete.

A key component of the lighter concrete, which weighs about 115 pounds per cubic foot instead of the normal 150, is special lightweight aggregate trucked in from Kentucky.

Lightening the deck reduces the amount of counterweight needed to balance it.

The counterweight, a steel frame supporting a massive block of cast-in-place concrete, sits just under the bridge deck when the bridge is closed and swings down into a pocket in the pier as the bridge deck swings skyward. Each counterweight weighs about 2 million pounds.

Says Teng's Jarmakowicz, "The bascule spans are designed so that the cantilevered deck and the compensating counterweight nearly balance on opposite sides of the drive shaft. It's like a teeter-totter that has one long lighter seat and one short seat with a heavy weight attached. Because of the balance, each bascule span can be raised and lowered at the required speed by just two 60-horsepower electric motors."

Because precise balance is so vital to proper raising and lowering, a specialty subcontractor will install strain gauges and equipment to allow monitoring of the balance during construction and to fine-tune the final adjustments.

Aesthetic Touches Will Add Visual Interest

In designing and constructing the Maple to Oregon Street Bridge, WisDOT, Teng and Lunda have all been attuned to the wishes of the Sturgeon Bay community.

That connection with the community has added some interesting aesthetic touches, including: the design of the bridge tender's building; the observation platforms extending from bridge deck, which enable people to stop and leisurely watch activity on the waterway; the brick-look pilasters that will support street lights on the bridge; the stamped finish that makes the concrete piers appear to be made from stone blocks; and down-lighting under the deck, which will artistically highlight the piers at night.

WisDOT Project Development Supervisor Steve Noel explained, "With any bridge or highway project, WisDOT tries as much as reasonably possible to accommodate the needs of the local community. We generally plan some amount into the budget to accommodate those kinds of requests and we work toward a result that makes everyone as happy as possible. This bridge is right downtown in a tourist area, so aesthetics are important," said Noel.

Efficient Controls; Flexibility For Future

One operator will be able to open and close the bascules from a single control house on the north side of the opening.

Seven waterproof cables buried in a trench two to three feet beneath the canal bottom carry electrical, control and communication wiring from one side of the bridge to the other. All of the operating systems and controls have backups to assure the bridge will always be operable.

To be absolutely certain the underwater cables all lay properly in the trench, Lunda verified their positions with sonar before backfilling.

Each of the underwater cables has a hollow tunnel through the middle to permit pulling of additional wiring if it's required in the future.

In addition, fiber-optic wiring is being run onshore from the new Maple to Oregon Street Bridge. Future plans call for running the cable to the existing Michigan Street Bridge so that both bridges could be operated by one tender.

When construction is done in September, Sturgeon Bay will have a beautiful new bridge that will carry vehicle traffic through its downtown, allow vessel traffic to travel the canal, and be pleasing to look at — a winning project all the way around.