I-255 over the Mississippi River

Illinois Department of Transportation | St. Louis, MO
aeria view of the tied arch bridge carrying I-255 over the Mississippi River

The Illinois Department of Transportation needed to replace the I-255 over the Mississippi River because the existing undersized steel truss bridge had become obsolete and was prone to frequent closure due to flooding.

Benesch designed a new twin, tied arch structure consisting of 15-span structures, each with 14 piers and two abutments. The superstructures are 52 feet wide, each consisting of an eight-inch reinforced concrete deck supported by 3,093 linear feet of welded plate girder approach spans and 910 linear feet of tied arch span over the navigation channel.

Although box section arch tie girders were typical on bridges of this type, these structures utilized an I-shaped section. The replacement design also greatly simplified connecting details and fabrication while reducing the potential for harmful secondary stresses.

The new structures were also embraced on a local level. Describing the bridge’s singular engineering qualities, the St. Louis Post-Dispatch stated,” “Once in a while engineering and architecture, function, and form, utility, and beauty, meet as equals in a triumph of design. Everything in sight works and looks good at the same time.”

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  • 1992, Eminent Conceptor Award, American Council of Engineering Companies - Illinois
  • 1985, Innovative Structure Award, Structural Engineers Association of Illinois