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Lateral braces are being added to the I-74 bridge arch. What's up with that?

Lateral braces are being added to the I-74 bridge arch. What's up with that?

  • Updated

Another target on the construction timeline for the new Interstate 74 bridge is being missed.

Planners from the Iowa Department of Transportation expected to see more segments of the arches raised by now, but "progress has been slow," said Danielle Alvarez, I-74 project manager for the DOT.

"Meeting our completion goal of the first half of 2020 will be challenging, and we're working closely with the contractor to determine how best to proceed to complete the bridge as quickly as possible while maintaining safety and quality," Alvarez said this week.

The westbound (Iowa-bound) span originally was scheduled to be finished this season. A particularly harsh winter led to some setbacks, but the record-breaking spring flooding delivered even more damaging blows to the construction timeline.

The first pieces of the bridge's signature arches were set in early March. At that time, a construction engineer with the DOT said the arches would take "several months to complete." Seven months later, the arches are not quite halfway finished.

While weather has been cooperative for several months, the process of raising the 34 segments of arch that are needed for the westbound span has proven even more difficult and time-consuming than originally predicted.

Transportation officials have warned since early in the year that the arch-raising process is tedious. The work is precise, given the arches originate on both sides of the Mississippi River's channel, then rise 164 feet above the bridge deck before coming together.

One of the most time-consuming elements of the process has been the construction of the pulley system that will help guide the arches toward their meeting point. A series of cables had to be meticulously threaded into the 200-foot-tall blue/green towers from housings that were built onto piers near the shorelines. The collections of cables then attach from the towers to the arches.

Another step in raising the arches began this week with the addition of lateral braces between the arches. The braces will give the arches more stability as they extend outward.

"The temporary bracing has been a part of the plan for the arch erection process," Alvarez said. "There are a lot of steps to erect the arch."

Despite the diminishing construction season, she said, the raising of the arches will continue as long as weather allows.

"Winter weather could make it more difficult to perform certain tasks, but we do not anticipate shutting down arch operations," Alvarez wrote in an email Thursday. "Barring extreme winter weather and temperatures, the arch erection process would be able to continue.

"At no point would the arch be left in an unstable position."

The temporary braces will be helpful, she said, when more arch segments are added, and the contractor begins setting the struts. The struts are the pieces near the top of the arches that connect the two sides.

When the arches are finished, the sections of roadway that go between them will be brought downstream on barges from their staging area along Moline's Ben Butterworth Parkway.

A large, city-owned parking lot is being used as a "lay-down yard" for the pre-assembly of the arch floors. The arch segments are 8 feet wide and 10 feet high — large enough for maintenance workers and inspectors to easily walk through.


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