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'Mechanical malfunction' strikes new I-74 bridge

'Mechanical malfunction' strikes new I-74 bridge

Record-breaking weather events haven't been the only foes of Interstate 74 bridge construction.

Department of Transportation officials have been saying for more than a year that the real challenge will be the "uniquely designed" arches in the likeness of basket handles that will rise high above the Mississippi River. And their assessment was correct.

Workers have been toiling for more than a week on the large cables that must be attached to the 200-foot-tall blue towers that were erected just behind the arches on either side of the river. The cables are to be attached to the tower, then used to hold the arch segments in place and, ultimately, guide them into position as they meet over the river's channel.

Though the arches over the new westbound (Iowa-bound) span originally were scheduled to be completed this spring, the schedule has sustained multiple blows, due to the harsh winter and long, repeated spring flooding.

More recently, another problem arose: A winch that was being used to pull the critically needed cable to the top of the tower suddenly gave out.

"Last week we were installing the stays and there was a mechanical malfunction which caused the stay to fall," said Doug McDonald, construction engineer for the Iowa DOT.

No one was injured.

If something unusual happens during the day in the I-74 bridge construction zone, chances are good someone will see it. The bike path that runs parallel to the work on the river in Bettendorf is a popular place for the curious to observe progress. Among the onlookers Tuesday were a retired engineer and retired contractor.

A third man with an engineering background said he happened to be watching the work last week when he, "heard a loud snap, and the cable just swung down to vertical."

The DOT confirmed this week that the winch failure was the mechanical malfunction.

"Installing and connecting the (cable) stays and the pulley system is a difficult process and requires extreme precision, because the stays will be used to adjust the angle of the arch segments to ensure the correct fit," McDonald said. "... The process is very complicated, which is not surprising given the unique design of the bridge."

An internet search for U.S. bridges with the basket-handle feature produced multiple examples of the design, including a bridge in Minneapolis (Lowry Avenue). That bridge was built by Lunda Construction, which is the main contractor for the I-74 bridge, and it also crosses the Mississippi River.

Recent projections by the DOT have the westbound span opening in the first half of 2020, rather than this fall as originally planned. Raising of the arch segments is expected to advance more rapidly when the cable stays are in place.

The completed arches will each contain 30 segments.

"Ten segments have been erected and, once the cable stays are installed, we will continue to erect the next segments on both sides of the channel," McDonald said. "When the arch is complete, we will have a more accurate picture of the schedule."

The completed arches must be in place before the roadway between them can be built and its surface poured.

The tedious nature of the work was clear to those observing the cable-raising efforts Tuesday. For more than an hour, at least a dozen workers on barges and waiting atop the blue towers could do nothing but watch. The cable was raised so slowly, the movement was nearly imperceptible.

Some onlookers took turns sharing binoculars to discern whether the cable was moving.


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