Walden Bridge (VT 15-83)
When challenges precluded maintaining traffic on the Walden Bridge over Joe’s Brook in Walden, Vermont, due to its narrow width, designers vowed to local citizens the closure would be minimized. To meet the 28-day schedule, they designed a precast, prestressed structure featuring NEXT D beams and beat the deadline by one day.
The bridge replaced a deteriorated single-span, two-lane structure built in 1933, explains Carolyn Carlson, senior structures project manager at the Vermont Agency of Transportation. “We considered a number of alternatives before concluding that the NEXT D beams offered the best option to meet all of the goals for us and the town.”
A complete replacement was recommended, and initially the plan was to put in a temporary bridge. But that proved unfeasible due to the terrain and other factors. Then they evaluated closing one side of the bridge at a time, but it was too narrow to make that a possibility. Engineers had stayed away from the option of closing the bridge due to the necessity for long detours through neighboring towns. The combination of added user time and disruptions to local roadways made it imperative that the closure be minimized.
Designers promised the local communities that the closure would last no longer than 28 days. To meet that schedule, they prefabricated as many components as possible so they could be quickly installed when the original bridge was demolished. J.P. Carrara & Sons Inc. fabricated the NEXT beams, while S.D. Ireland Companies cast the footings, abutments, and wingwalls.
The new bridge, which is 58 feet long and 34 feet wide, features cast-in-place concrete sub-footings that were formed and poured on ledge to provide a level surface for the precast footings to be set on. The abutment and wingwall footings, abutment walls, wing walls, and NEXT D beams were trucked to the site and lifted into place in sequential order as they arrived.
Four modified NEXT 28D beams, consisting of two beams apiece, were used. The beams, 55.76 feet long and 8 feet wide, included a 25-degree skew and precast curtain walls. The fascia beams had 3-inch curbs poured integrally with the beams and used Level 2 dual-coated Z-Bar reinforcement. The concrete offered a release strength of 8,000 psi and a 28-day strength of 10,000 psi. After the bridge was installed, the deck received a 3-inch pavement, and the bridge railing was installed on the curbs.
The schedule was outlined in the contract with incentives for beating the 28-day deadline and disincentives for surpassing it. “We want to encourage the contractors to be successful in these situations, and we did everything possible to help them meet or exceed the date,” says Carlson.
The bridge was completed in 27 days, keeping everyone happy and providing a new bridge with a long service life for the community.
(Abutments, wing walls and footings) S.D. Ireland Companies, Williston, VT
Structural Precast Elements:
• Total beam weight: 100,000 lbs.
• Level 2 dual-coated Z-Bar reinforcement
• Precast concrete abutments, wing walls, and footings