It’s not very often that arch bridges are built anymore. For one thing, they require more engineering than other bridges. Although they are more expensive than the plate girder bridges that are typically built these days, an arch bridge is being built over the Connecticut River between Brattleboro, VT, and Chesterfield, NH.
“You just don’t see anything like it. I doubt if anyone working here has done one before,” commented Dale Andrews, project superintendent for Cianbro Corporation of Pittsfield, ME, the primary contractor for the job.
The new arch bridge replaces an old one that was originally built in 1939. It will be made of steel, coupled with concrete abutments and deck, and just like the older version, it requires an extensive support system.
The new bridge will be used for automotive and truck traffic for Route 9, which crosses the river at that point, but the old one is not being dismantled. Instead, it will be renovated — the deck must be repaired and stringers replaced — and be used for foot and bicycle traffic, according to Mark Moran, an engineer for the New Hampshire Department of Transportation (NHDOT).
The arch design was chosen for the new bridge primarily for aesthetic reasons, Moran explained. Because the old bridge will remain standing, the new one needs to reflect its style.
Things have gone smoothly with the arch bridge construction. “There have been a couple of hiccups, but we got over them relatively easy,” Moran said.
Work on the arch bridge is just one part of a project that actually combines several different bridges in the same vicinity. Work is being done with the cooperation of both the NHDOT and the Vermont Agency of Transportation (VTrans). New Hampshire authorities are overseeing the $15.4-million arch bridge construction, while the Vermont department is in charge of a new $4.7 million railroad bridge that will be built a short distance away.
The new arch bridge is 75-percent completed and is scheduled to be completed on time, October 2003. The Vermont project had been delayed and recently went out to bid.
Much of the work on the arch bridge is being done from a Flexifloat barge, measuring 60-by-100 ft. (18.3 by 30.5 m), floating on the river beneath it. Sitting on top of it is a 220-ton (198 t) Manitowoc crane, located so that all the pieces of the bridge can be lifted from that level. A 60-ton (54 t) Manitowoc truck crane also is in use.
It has been a challenge to keep river ice away from the barge, Andrews said. It also was a challenge to build the abutments on the Vermont bank because of the rock ledge on that side. The earth bank on the New Hampshire side made it easier to build abutments. Pile driving is being done with machines from ICE (International Construction Equipment).
Once the new arch bridge is completed, it will span 426.5 ft. (130 m). No detours are needed because traffic will continue to use the original bridge until the new one is completed.
In early January, work on the new bridge had progressed enough so that the two of them sat next to each other, like identical twins. The new one is slightly wider measuring 50.8 ft.(15.5 m) across. A pedestrian walkway that is found on the old one was not included on the new one. Two temporary erection towers holding the cables will be dismantled soon.
Cianbro is an ideal company for the job because one of its niches has been steel erection ever since the 1940s, said Moran of NHDOT. “They are fantastic. They are amazing to watch. No detail has gone unturned,” he said.
“This project has been a pleasure to work on,” commented Andrews. “The steel erection was unique and challenging and the owner was great to work for.”
The major subcontractors on the project are Lane Construction of Meriden, CT, paving, and S.U.R. of Rochester, NH, utilities and earthwork. Andrews said that quite a bit of dirt is being moved, including the rock ledge on the west side of the river.
The new arch bridge is the first part of the entire project. Soon, a new railway bridge across Route 9 will be constructed, a job under the jurisdiction of VTrans. The railroad tracks will be moved because a roundabout at the intersection of Routes 9 and 5, a short distance to the west, is being reconfigured, according to Alec Portalupi, project manager for VTrans.
Currently, Route 9 is a two-lane highway passing underneath tracks owned by New England Central Railroad. It is what Portalupi described as being a snug fit. Plans are under way to make the roundabout larger, which will force the route of the railroad farther to the west. The road is being widened to four lanes so that the new bridge will be longer.
Several other alternatives were considered that would have kept the old bridge intact, but they were dismissed because they would have impacted a number of local businesses.
“We needed a permanent shift in the rail line,” Portalupi said. Because the area being affected is so tight, it is being done in “kind of a phased approach,” he added.
