The Illinois Department of Transportation selected Benesch to provide design engineering services for the construction of a new bridge carrying I-57 over the Mississippi River in Cairo, IL. Benesch evaluated thirteen types of structural systems for the four-lane bridge design. The optimum design alternative featured a three-span (517 feet – 821 feet – 517 feet) continuous truss, with the center span designed as a tied arch. The river piers, now supported on open dredged caissons, rest on dense sand over 80 feet below the river bottom. The approach spans feature a series of three and four units with lengths between 300 to 400 feet. The design team used a stringer-type system, resulting in a minimized overall cost by being the least expensive system to construct.
Located in an earthquake zone, the bridge was designed for a minimum of six percent lateral load in any direction. The two center piers have fixed bearings, and all bearings were designed for an uplift equal to five percent of the dead load reaction. A special computer program was developed for this project. This program designed and plotted the bridge joints, positioning them on the sheet for use in the final plans.