Rebuilding the Fox River Bridge

by Rob Koss

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016-Gantry-System- resizedRebuilding the Fox River Bridge in Elgin, Illinois, is one of the largest single awards in the $2.5 billion rebuilding and widening of the I-90 Jane Addams Memorial Tollway between the Tri-State Tollway (I-294) and Rockford. Originally opened in 1958, the six-lane bridge is being replaced with two side-by-side bridges, 1,315-feet long, standing 40 feet above the Fox River. The new structure will increase capacity to eight lanes with full shoulders in each direction. The bike and pedestrian bridge that runs under the structure are also being replaced.

The $95 million Illinois Tollway project, designed by Stanley Consultants, began in 2014 and is scheduled to be completed by the end of 2016.  As of mid-July, the entire bridge substructure had been completed, except for abutments. Eastbound beam erection and deck widening is finished and westbound deck construction is in progress. Homer Chastain is providing construction management services.

More than 100,000 vehicles travel across the Fox River Bridge each day. That equates to nearly 110 million vehicles traversing the bridge during the three-year construction period. Maintaining traffic flow while simultaneously demolishing the existing structure and building a new one is traditionally accomplished by developing a multi-staged plan that jockeys traffic back and forth across the bridge section with split counter-flow lanes and numerous sub-stages.

However, by selecting girders that significantly increase the structural depth of the bridge, it became possible to construct the entire substructure of the new bridge underneath the existing bridge. This significantly lessens the impact to traffic by allowing the contractor, a joint venture between Kenny Construction Co. and Kraemer North America, to continuously construct the new substructure under the existing bridge without interruption—even through the winter. This made it possible to reduce the maintenance of traffic scheme to just three stages.

020-Gantry-System resizedA gantry system, used instead of conventional cranes to perform the heavy lifting, also improves traffic flow by allowing all six lanes to remain open during construction. The gantry uses a hoist traveling along an overhead rail to lift and set the heavy beams, each weighing nearly 100 tons. All pier elements, including pier caps, are being constructed under the bridge while maintaining all traffic lanes above, which allows the contractor to work unobstructed.

The gantry system includes three main frames positioned 150-170 feet apart. Each main frame has a column on each end supporting overhead beams with cross bracing between them to carry two hoists and a trolley system to lift and transport the concrete beams from the delivery truck to bridge piers. Two gantries are used to set each beam, with one gantry on each end. Once the beams are set at each pier the gantry frame is disassembled and moved to the next open pier, moving first eastbound and then repeating the process on the westbound lanes.

The process will ultimately engulf and replace the original structure while maintaining three lanes of traffic in each direction nearly 100 percent of the time, a convenience that would not have been possible using cranes. These innovative engineering and construction techniques are expected to shorten the construction period and are also anticipated to save $2.2 million in maintenance costs over the life of the new bridge.

The new Fox River Bridge will have eight spans and seven piers—versus the original structure’s 14 piers—which reduce the environmental impact on the waterway and rare forested fen below. Existing storm sewers that previously drained into the fen have been eliminated and a new drainage system will capture all bridge stormwater runoff and treat the flow prior to discharge into the river.  These flows are being rerouted, to preserve the quality and quantity of groundwater within the adjacent forested fen communities.

“This state-of-the-art bridge is being built with the most advanced techniques to shorten construction time and reduce any inconvenience to Tollway customers by maintaining three lanes of traffic in each direction at all times except for off-peak overnight hours when traffic flow will allow,” said Illinois Tollway Chief Engineer Paul Kovacs. “When it is completed, the new bridge will safely accommodate more vehicles while also protecting the Fox River and nearby wetlands from stormwater runoff.”

Rob Koss, P.E., operations manager, Stanley Consultants Chicago Office, project manager for the design of the Fox River Bridge: 773.714.2003

Photos courtesy of Stanley Consultants.

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