Last span poured to finish deck of Penobscot bridge

VERONA ISLAND – It’s a bridge.

Crews from Cianbro and Reed & Reed poured the final section of the main span of the Penobscot Narrows Bridge and Observatory last week, and the bridge deck now stretches across the Penobscot River from Prospect to Verona Island.

The bridge also is anchored to the land on both shores, although crews still have some work to do on the concrete abutments before the new span can be connected to a newly configured Route 1 in both towns.

The large cable stays have all been tightened or “stressed” to their designed levels, although some adjustments may need to be made once all the work is completed. The critical work being done now, according to Tom Dow, project manager for the Maine Department of Transportation, is adding tension to the bridge deck. Workers on Friday were inside the hollow bridge deck, known as the box, running tension cables inside channels within the concrete deck structure to create compression there.

“The closer you get to land, there are less and less stays creating compression, so there is less compression in some places,” Doe said Friday. “We’ll add tension on these cables and squeeze the deck segments, so the compression is uniform all the way through the bridge.”

Closing the span in the middle was the final key element in the bridge construction, said Chris Burgess, the lead engineer for the design team from Figg Engineering Group in Tallahassee, Fla.

He said it was a good feeling to see the two ends connected.

“It’s incredible,” he said. “For a bridge engineer there is no greater satisfaction.”

Though some locals liked to speculate whether the two ends of the span would meet, Burgess said, crews took measurements constantly to ensure that both segments of the bridge were being built where they needed to be in order to meet in the middle.

The bridge segments were poured in place and after each segment had been poured and the concrete cured, crews monitored the geometry of the bridge, Burgess said.

“Once the cure was completed, we could monitor the shape of the bridge and then make a projection as to how to aim the next piece,” he said.

The bridge deck moved up and down throughout the construction process, he said. As each segment was poured, it added weight to the bridge, which made the deck dip. Then the cable stays were tightened, pulling the deck up into place. As the segments of the main span got closer to the center of the river, the dip after each pour became greater and more noticeable.

After the last segment before the keystone piece was poured, the span from the Prospect side of the bridge was 26 1/2 inches lower than the Verona side span. That generated a few phone calls and e-mails to the DOT from concerned bridge watchers, but they needn’t have worried.

“That was very close to where Chris said it would be,” Doe said.

Providing tension to the last cable stay took care of the discrepancy.

“We stressed stay number 20 and took the slack out of the cables and that lifted the lip up to match,” Burgess said.

The same kind of attention was paid to the left-right alignment of the bridge with adjustments being made throughout the project. When all but the closing segment was done, the two sides of the main span sections were within a quarter of an inch of each other.

“That’s a small difference,” Burgess said. “Well within tolerances.”

There is still work to be done before the bridge is completed. Items such as the bridge railing and lighting must be installed. A stainless steel roof, which will house a warning light in the peak, needs to be installed on each of the pylons, and work needs to be completed on the concrete median strip between the two lanes of the bridge.

Crews will connect the ends of the bridge to Route 1 within the next several weeks in time for the Oct. 14 community celebration. “Bridgewalk” will allow pedestrians to walk from one end of the bridge to the other.

Work on the elevator and the observation deck continue, although the elevator is not yet operational and the observation deck is still an open concrete framework. The observatory will not be open for the Bridgewalk, but people will be able to visit the entrance at the base of the pylon that day.

The observatory is expected to open next spring. The views from the deck are truly spectacular, providing a 360-degree panoramic view of the surrounding area. On a clear day, visibility will be 100 miles in all directions, making much of the Penobscot River valley and Penobscot Bay visible to visitors.

The bridge is expected to be open to vehicular traffic before the end of the year.