MIDDLEBURY — Workers will spend the rest of this month and next completing the basic framework of the new Cross Street Bridge, then shut down major operations until early April with the goal of having the span ready for traffic by next Thanksgiving.
It has been an eventful fall for the project, culminating in the recent trucking, through downtown Middlebury, of a series of massive concrete beams that have now been swung into place between piers on each side of the Otter Creek.
“We obviously have the piers in, most of the major beams in — which is a big step,” project coordinator Dave Hallum said in an interview with the Independent this week.
Construction workers are now completing work on the joints between the bridge girders, installing rebar and fashioning the sleeves that will accommodate the cables that will be used to “post-tension” the beams so that they can be slightly raised for removal of the temporary steel piers that now support them.
Here’s how the post-tensioning process will work: Five cables will be strung inside (toward the bottom) of the concrete beams. These cables, strung along the entire length of the beam system, with be pulled taut with the aid of a 500-ton hydraulic jack, according to project engineer Chris Goodrich of VHB Inc., lead engineers for the project. J.P. Carrara & Sons has been in charge of manufacturing the concrete components of the span.
This post tensioning will cause the beams to raise a few inches, thereby lifting them off of the temporary steel piers. This will allow crews to remove the piers from a temporary, man-made island in the Otter Creek. Hallum said the workers will try to pull the piers out from where they are embedded in the Otter Creek bed. Failing that, the steel would be cut above the creek water line, so they are visible to any cold-weather kayakers. Then workers would return in the spring to cut the steel at its base.
Most of the steel pier infrastructure, as well as the rocky/gravel base in the creek used as the temporary staging area, are to be removed by the end of January, according to Hallum.
Bridge work is then set to go on hiatus until around April 1, when activity will kick back into gear with construction of the connector road behind the Middlebury municipal building that will link College Street with South Main Street. At the same time, workers will begin installing some of the concrete box beams between the bridge piers and abutments. These are the girders that will connect the massive beams set in place this month with the road at either end of the bridge.
Plans call for related improvements to College and Cross streets to begin in early May and continue into August, according to Hallum. In the meantime, the bridge’s concrete deck will be poured and cured, with paving of the deck slated for June.
One of the most complex and potentially disruptive aspects of the project is to begin at the end of June: The new roundabout intersection that will link College, Cross, Main, Park streets and Bakery Lane in downtown Middlebury.
“That will be big,” Hallum said of the rotary work.
The final, major road improvements will center on the intersection of Cross and Court streets and at Water and Cross streets.
“We are still looking to finish the project no later than November of 2010,” Hallum said. “People will be driving on that bridge by Thanksgiving of next year. It’s exciting; it’s moving very fast.”
Once completed, the Cross Street Bridge will have a unique distinction. It become the longest pre-stressed, post-tension, bulb-T girder concrete span in the world, according to Hallum. He explained the bulb-T girders are commonly used in smaller bridge construction, but nothing of the magnitude of the 240-foot-long Cross Street Bridge. The reason this technique is being used here is because it is allowing the bridge to span the Otter Creek without the benefit of an extra pier in the creek itself. State officials had warned of potential environmental permitting problems if the bridge required placement of a pier in the water.
“It is pretty impressive,” Hallum said.
State officials have been closely monitoring the Middlebury project, which is a collaboration between the town and Middlebury College. The college is contributing $9 million of the $16 million in project costs, while the town is providing the remainder through a series of local option taxes that kicked in in October 2008. The town is following a “design-build” process for the bridge project, which is proving more expeditious than the state’s customary “design-bid-build” process for major projects, noted Middlebury Town Manager Bill Finger.
“We set the price up front and you work out the details as you go,” Finger said. The state’s “design-bid-build” process tends to involve more bureaucracy and permitting considerations.
Finger said he has been pleased with how the project has been progressing.
“It seems to be working quite smoothly, resulting in a good product,” he said.