The December holidays arrived in Northeast Iowa with a bang, as a controlled demolition process brought down large sections of the nearly century-old Lansing Bridge.
Occurring on December 19, the implosion sent Wisconsin’s center and side spans of steel falling through the rebar structure into the cold Mississippi River. The remaining sections, which span residential homes and an active freight line on the Iowa side, will be phased out by Kraemer North America, which is building a new, wider 1,724-foot-long span less than 100 feet from the old bridge.
As the only crossing along a 70-mile stretch of the Mississippi River, the narrow 1,702-foot-long bridge, also known as the Black Hawk Bridge, was slated to remain in service until the $140 million replacement was completed. Repeated excessive movement of the old structure beyond safety thresholds forced extended closures and complicated Kraemer’s construction schedule, adding several months to the October 2026 target completion date.
Rather than risk more construction disruptions and to protect motorists, the Iowa and Wisconsin departments. of Transportation, which co-manages the Lansing bridge, chose to permanently close the crossing last October. Demolition moved forward in the winter, when the ice-choked Mississippi River was closed to barge traffic.
Kraemer Senior Project Manager Aaron Rosenbery says the revised schedule required compressing more than a year of demolition planning into a few months. The effort involved extensive coordination and clearance with multiple state and federal agencies, meetings with law enforcement to ensure public safety, and dry process. Final preparations, including pre-cut structural components for explosives, were further complicated by the weather, as an advancing cold front brought rain, blizzards, high winds and a 30° drop in temperature overnight.
“The next morning, we checked things again to make sure there was no effect of the flash freezing,” says Rosenbery. “Once everything was in place and ready, the explosion itself was pretty flawless.”
As planned, the implosion left a short period of approach on the Wisconsin side as part of a collaboration with Purdue University researchers to test the structural redundancy of critical fracture members. Loading the section with 150,000 pounds of sand and an array of sensors, the researchers planned to compare how well the team’s predictive models matched actual performance by using a load shaped to cut a critical stress diagonal.
According to Purdue civil engineering professor Robert Connor, the section performed much better than expected.
“Nothing happened,” he says of the small explosion. In fact, he needed to cut three additional primary tension members with an excavator-mounted shear attachment before the section finally collapsed.
In addition to demonstrating the actual structural redundancy of older steel bridges, a factor that Connor says was not considered when they were designed, “the test provides incredibly valuable data that we can use to calibrate our models and give us more confidence in our analysis of how a bridge will behave if a critical member fails for fracture. And we’ve found that these members are better in many cases than we give them credit for.”
With the old bridge literally and figuratively out of the way, Rosenbery says steel erection for the new bridge will continue apace through the summer, with the 334-foot-long center section scheduled to go up with jacks in July.
“The only uncertainty will be the spring floods and their effect on our water operations,” he says, adding that the project is now due for completion in the spring of 2027.
