Thetford Center Covered Bridge - Sayre Bridge, Thetford Vermont
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- Vermont
- Covered Bridges
- Haupt Truss
The Thetford Center Covered Bridge is unique in Vermont; it is the only covered wood bridge supported by Haupt patent trusses. According to Richard Sanders Allen, it is also the only Haupt truss covered bridge in the Northeast U.S. Although altered so that the Haupt trusses no longer carry the deck, the bridge retains intact this unusual truss system. The Thetford Center bridge is one of two covered wood bridges remaining in the town of Thetford.
The covered bridges of Vermont are among its most cherished and symbolic historic resources. About one hundred bridges still stand in the state, the greatest concentration by area of covered bridges in the country.
Bridge Description
The Thetford Center Covered Bridge consisted originally of a single span supported by two flanking timber Haupt trusses.
In 1963 the bridge was altered significantly; the timber deck structure was replaced by four longitudinal steel beams and a central pier was built under the span. The Haupt trusses now carry only the superstructure of the bridge. Each truss combines a series of timber diagonals and uprights (similar to multiple kingposts) with a laminated plank arch; the arch comprises three layers of heavy planks pegged together vertically.
The abutments were built originally of irregular stone laid dry. During the structural alteration, both abutments were capped with concrete to receive the steel deck beams. The lower part of the west abutment has been faced with concrete. The narrow central pier is built of reinforced concrete.
The bridge is 128.5 feet long at floor level. The ends of the side walls flare upward so that the gable ends overhang the floor about one foot at each portal. The pier stands under the midpoint of the original span. The bridge is 20.5 feet wide and has an 18-foot roadway. The wood floor, which consists of planks laid on edge directly on the deck beams and transverse to them, begins seven feet inside each portal.
On the exterior, the timbers pegged together to form the trusses (and side walls) of the bridge are sheathed with unpainted flush boards hung vertically. One small rectangular window has been cut in the middle of each side wall. The gable ends are sheathed with flush vertical boards painted red. The portal openings are rectangular. The medium-pitch roof, which does not overhang the gables, is covered with corrugated metal sheeting.
Interior, showing west truss (1973)
