This project was borne out of the need to improve an interchange at the north end of the Murray Baker Bridge in Peoria, IL. The interchange was built in the late 1950s and had numerous design deviations from current standards, including several sub-standard safety features. Several places within the interchange had accident rates that were more than ten times higher than statewide averages. Thus, the interchange needed improvement, but the proximity of the truss posed a significant site constraint.
Benesch’s role was to perform the necessary preliminary engineering to identify an acceptable solution that incorporated the existing bridge into a reconfigured interchange. Benesch conducted a Value Planning Study to weigh the options – one of which was a $50 million complete bridge replacement. A different, innovative idea that came from the study was to shorten the bridge truss – which came at a price tag of $3 million.
This solution proved to be extremely complex, and was the first known truss shortening of its kind. Determining how much of the truss to remove, and the method to do it, was crucial to maintaining the balance of the suspended spans since there was the possibility of a dangerous energy release if the truss was cut abruptly. Benesch and the contractor devised a load transfer device that relieved the force gradually, thereby making it possible to cut the truss safely.
Shortening the truss was the pivotal component of an economical bridge rehabilitation, as well as the key to designing an interchange that improved the connection between I-74 and Peoria and enhanced public safety. It allowed for a safer solution at a lower cost, while preserving the existing structure. It was a prime example of a sustainable solution – balancing social, economic and environmental features.