MIDDLEBURY — Extensive rehabilitation of the historic covered Pulp Mill Bridge is proceeding smoothly and is on target to be completed by November, according to the Vermont Agency of Transportation (VTrans) and Alpine Construction, which is doing the work.
Crews this week continued to take advantage of good weather to install new timber in the span that links Middlebury with Weybridge across Otter Creek via Seymour Street. Joe Knipes, resident engineer for VTrans, said that more than half of the wood in the 193-year-old span will have been replaced by the time the $3,344,758 project is finished.
“From the deck down, it is probably 80 percent to 90 percent new,” Knipes said on Monday.
Work began Jan. 2 on the bridge, which had showed some sag and deteriorating members as well as other deficiencies. The span had been on the docket for repairs for several years and in the meantime was limited to handling one vehicle per lane at a time.
Alpine Construction, based in New York, was hired to rehab the bridge in a manner that will maintain its historic integrity. So while vast amounts of new timber will be used, they will be installed and fitted in a manner that respects 18th-century building techniques — including mortise and tenon joints.
Supervising this process is Jim Ligon, Alpine Construction’s project superintendent. With the buzz of saws and thud of hammers echoing through what is one of the few functioning, double-laned spans in the country, Ligon explained how the work has unfolded.
First, crews put steel beams underneath the timber structure to support the bridge while it was being painstakingly dismantled. Workers removed the decking, put in a temporary work deck, then replaced the lower horizontal beams, known as chords, and posts. Then it was time to replace the top chords, some of the rafters and some of the diagonal work. Three of the arch ends needed to be repaired.
Everything installed below the deck had to be specially treated with a substance to prevent insect and fungus damage. The timber above the deck has not been treated, according to Ligon.
After completing rehab of the interior of the bridge, workers will install a new standing seam roof and repair the siding.
It has proved to be somewhat of a jigsaw project, Ligon acknowledged, making sure all of the various components of the structure are properly re-installed. Complicating matters is the fact that the original builders didn’t quite get the Pulp Mill Bridge right when they erected it, according to Ligon.
“The patented Kingpost truss is a good design, if it’s built the way it’s supposed to be built,” Ligon said. “This one wasn’t. There were some mistakes made in the original build that have contributed to some of the failures the timbers have seen through the years.”
At this point, Alpine has completed more than 60 percent of the project, according to Ligon.
Some might be surprised to know that builders did not tap Vermont’s abundance of timber for the Pulp Mill Bridge project. Engineers picked Douglas fir as the primary replacement wood because of its composition and durability. Because mature Douglas fir cannot be found in Vermont it had to be sourced from the West Coast, Ligon noted.
Knipes said 24,000 board feet of wood is being used for the Kingposts and top cord; 31,000 board feet is being used for the bottom chords, decking and some of the floor beams; and 7,500 board feet is being used for the siding.
The wood is being put in place at a good pace, Knipes said.
“Things are going really well,” he said. “At this point, there is no reason to think (the November target date) won’t be achieved.”
Work has temporarily choked off a well-traveled route across Otter Creek. While this has pushed some more traffic on Weybridge and Academy streets, Middlebury Town Manager Bill Finger said he has not heard any complaints about the inconvenience to motorists.
Reporter John Flowers is at firstname.lastname@example.org.