Black Hawk Bridge pier. The piers date to 1931. They were becoming unmoored, apparently by vibrations from construction of a replacement bridge alongside.
The downside of solar-powered motion-sensors
LANSING, Iowa – Tremors in the Black Hawk Bridge over the Mississippi River went unnoticed for weeks because motion-sensors were solar-powered and the sun wasn’t shining. Television KCRG in Cedar Rapids unveiled the lapse. Asked about it, the lapse was confirmed byy Iowa highway department project engineer, Clayton Burke, confirmed the lapse.
Thr93-year-old narrow and outdated bridge was closed finally on February 26 when a kink in the bridge decking was noticed y a citizen – who, by the way, ,had no engineering background. The citizen called the sheriff, who immediately blocked access ramps at both ends. A few days later: Iowa highway engineers examined the bridge, found. Indeed, they said, the bridge was dangerously in motion. The reason; Probably vibrations from piers being pounded into the river bottom for a replacement bridge being built a few yards away.
Who asleep at wheel
Burke, the project engineer, pointed a finger at a contractor — Wiss Janney Elstner Associates of Northbrook Illinois. The company had installed motion detectors on the old bridge’s piers and abutments to catch vibration, displacement and tilt. Alas, the sensors were powered by solar panels. On cloudy weather days, those sensors didn’t pick up enough rays. Without power, the sensors would shut off until Wiss Janney Elstner could send an agent to reset them. This happened at least once in January and went un reported to Iowa bridge authorities, Burke said:
“A couple of times when the system came back online, it showed a certain amount of movement in those displacement sensors, but that was interpreted as some type of error that occurred due to the loss of power and that they needed to be recalibrated when they were turned on. In reality there may have been actual movement that those sensors were indicating. If we would have received that notification, we would have stopped work on the contract and reevaluate how the construction on the new bridge was proceeding.”
Don’t tread here. The bridge, which rises 60 feet over the Mississippi River main channel, has been closed since February 26.
As soon as Sheriff Clark Mellick shut down traffic over the bridge, Burke said, the contractor started digging through the data. “They looked at the dates they had recalibrated the systems,” Burke said. “I believe they took those calibrations out and they showed us the data and what it was actually recorded as and then we could see those movements throughout time after they performed that data analysis.” Queries for an explanation at its offices in a Chicago suburb, Wiss Janney Elstner were not returned.
Timeline for repairs
Estimates are that repairs on the old bridge could be completed by the end of April. Meanwhile, traffic is detoured 60 miles to the Wisconsin side via LaCrosse or Prairie du Chien. Alternatively, local entrepreneurs have been contacted to haul people across the river a few at a time in small fishing and pleasure boats. When will this all end? The new bridge, due for completion in 2026, will replace the historic Black Hawk Bridge, which will be torn out.