Structural Issues Force Early Demolition of Mississippi River Bridge

The Blackhawk Bridge linking Lansing, Iowa, and rural Wisconsin won’t survive to see its replacement completed, as both states’ transportation agencies have decided to close and demolish the nearly century-old structure about one year earlier than originally planned.

Privately constructed in 1931 on shallow timber pilings and managed by the states for the past 70 years, the 1,702-ft-long steel through truss bridge is the only crossing along a 70-mile stretch of the Mississippi River. The original plan called for keeping the bridge open until after Kraemer North America completed a new, wider 1,724-ft-long crossing, which is just 75 ft away.

Since construction began in late 2023, however, the old bridge has twice experienced extended closures—both the result of structural movement that exceeded safety thresholds. The repeated displacement issues have had a ripple effect on new bridge construction activity, pushing the project’s planned completion date from 2026 to 2027.

Although the existing bridge was deemed safe to reopen after the second instance of excessive movement this past May, further engineering analysis by Wiss, Janney, Elstner Associates and extensive discussions between the state DOTs and Kraemer determined that closure and demolition offered the best approach to ensure safe and timely construction of the replacement bridge.

“The further we refined the analysis, the more assumptions our engineering consultant had made about the condition of the existing structure and preexisting stresses in the various members,” explains Iowa DOT project manager Clayton Burke. “The decision came down to uncertainties surrounding the assumptions we would have to make and the risk of failure if any of those assumptions were wrong. It was determined we had pushed as far as we safely could without putting the public, the workers, the navigation channel and the railroad at risk.”

Based on the analysis and a thorough inspection, the DOTs have determined that the existing bridge can safely remain open in its current condition while demolition planning is underway, Burke adds. Final closure is expected this fall.

Kraemer senior project manager Aaron Rosenbery says the old bridge’s center span and eastern spans will be removed using controlled demolition. The remaining portions, which include span 1 and the western cantilever, will be deconstructed piece-by-piece in to protect an active rail line and adjacent buildings on the Iowa side and to minimize disruptions to river traffic.

While pile driving for the temporary shoring towers is on hold until after demolition is complete, Kraemer is proceeding with final pours for the new bridge’s concrete piers. In a change from the original construction plan, steel erection will proceed west to east from the Iowa side. Cantilever construction from Piers 2 and 3 will be used above about half of the new 750-ft-wide navigation channel, with the final line—a preassembled 334-ft long center span—to be hoisted up from a barge and set in place.

Meanwhile, the project team is using the old bridge’s final weeks of service to investigate opportunities for alternate river crossings to support businesses, institutions and commuters during what could be up to two years of construction. Options under study include restoration of a water taxi service offered during previous closures. The DOTs are also working to minimize construction and other disruptions on roadway detours.