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The motivation for shortening the Murray Baker Bridge truss in Peoria on Interstate 74 was not the bridge itself, but the adjacent Adams Street Interchange.
The interchange was constructed in the late 1950s, before interstate or interchange standards had even been developed.
In addition, the original design never anticipated the speeds and traffic volumes that the facility has endured. The interchange had the dubious distinction of having some of the highest accident rates in the state, more than ten times higher than state averages.
Riverfront Site
Although the truss is symmetrical, the deeper portion of the river used for the navigation channel is not centered between the banks.
As a result, the northern end of the truss, which includes the entire first span, is over land and not water. The situation afforded the opportunity to shorten the truss without introducing additional piers in the river.
The Adams Street Interchange is situated immediately off the northern end of the bridge. The need to redesign the interchange was stymied by the presence of the bridge.
The proposed new interchange ramps required long tapers that conflicted with the truss. The north approach spans could be widened to accommodate the ramp tapers, but widening the truss was not seen as a practical alternative.
Shortening a major cantilevered truss has apparently never been done.
Use of the load transfer device and the heat/yielding technique have been used elsewhere in various forms but is uncommon and adds to the uniqueness of the Murray Baker project.
The removal and replacement of all 16 original truss pins is unusual. Instrumentation was used to monitor the loads.
The design team developed a set of criteria that included the following:
* The need to accurately model the effects on truss members and connections.
* Avoiding an abrupt energy release throughout the truss.
* Avoiding large deflections of the truss.
* Avoiding racking of the structure by working on both trusses simultaneously.
* Strengthening members with large forces.
* Avoiding damage to the existing and proposed utilities underlining the bridge.
* Developing alternative routes to facilitate bridge closure during construction.
One fixed bearing supporting the truss was removed and replaced and required a jacking load of about 4 million lbs.
The jury said, "We wish we had built this. Anything that saves the taxpayers $25 million is worth it."
Key Players
Owner:
Illinois Department of Transportation District 4, Peoria
Prime Contractor:
United Contractors of the Midwest, Springfield, Ill.
Subcontractor:
Halverson Construction Co. Inc., Springfield
Design Consultant:
Alfred Benesch & Co., Chicago
Structural Consultant:
Hanson Professional Services Inc., Springfield
Structural Consultant:
Wiss, Janney, Elstner Associates Inc., Northbrook
Structural Consultant:
Applied Research Associates Inc., Champaign
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