Relocating part of a busy interstate that links Illinois to St. Louis was just one of the many challenges faced by the Illinois and Missouri Departments of Transportation. Their goal was to select a bridge type, with the winning structure being a river spanning cable stayed bridge. Such an ambitious project required someone with expertise in designing long, river spanning bridges and expressway/interchange planning and design, not to mention the ability to oversee an array of multidisciplinary design firms. They selected Modjeski and Masters for both the bridge studies and preliminary and final bridge designs. The task included an 18-month bridge type selection study, with the winning structure being a river-spanning cable-stayed bridge.
The I-70 Mississippi River Bridge would be no ordinary structure. With a width of 222 feet, it would be the widest cable-stayed bridge in the world. Four traffic lanes, plus two full shoulders in each direction, would carry the relocated Interstate 70 and Interstate 64. A plan to accomplish all these objectives would have to be extraordinary as well. Our design called for several innovative features: two single-pylon towers, inclined nine degrees from the river, which would eliminate obstructions to river traffic; a main channel span of 2,000 feet; and three planes of cables.
During the bridge type study phase, a comprehensive vessel collision study was performed. We collected and analyzed data that included waterway characteristics, a history of marine accidents in the region, and vessel traffic characteristics and navigation conditions. To eliminate the potential threat of a vessel impacting the vital structure, and at the same time satisfy the demand for a massive and recognizable landmark, the winning cable-stayed bridge would span the entire width of the mighty Mississippi River with no piers in the water. Equally important was the extensive site-specific seismic analysis of the bridge, which sits within the New Madrid Seismic Zone. The resulting solution featured several internal design mechanisms to help minimize and redistribute stresses caused by a seismic event.
This project is yet another example of Modjeski and Masters bridge engineering that sets the standards of design ingenuity for the industry to follow. However, following a shortfall in funding for the mammoth river crossing, a down-sized alternative is currently being investigated.
With a bridge width of 222 feet, this would be one of the widest cable-stayed bridges in North America.
Dr. John M. Kulicki, PE, SE (Principal In Charge)
Todd B. McMeans, PE (Project Manager)