Swanton Covered Railroad Bridge, Swanton Vermont
The Swanton Covered Railroad Bridge was the longest of the three covered railroad bridges remaining in Vermont. It was destroyed by fire in 1987.
The structure was built in 1898 to connect what is presently the St. Johnsbury and Lamoille County Railroad, a lateral line running from St. Johnsbury to Swanton, Vermont, with the main north-south line of the Central Vermont Railroad directly west of the river.
The structural integrity of the bridge, from abutments to trusses, remains substantially unimpaired.
The pragmatic uses of various structural systems within the bridge and the presence of both pegged and bolted bridge joints document the transition of bridge-building technology at the turn of the 20th century.
The tracks leading to the bridge have been removed and the structure is presently not in use.
Bridge Description
The Swanton Covered Railroad Bridge crosses the Missisquoi River several hundred yards south of Swanton's central business district.
The bridge is built in three approximately equal spans and has a total length of 369 feet. The structure is supported at either side by a continuous Town-Pratt double lattice truss. A three member, multi-segmented chord, running the entire length of the structure, is located at the top and bottom of the main trusses. Diagonal timber lateral bracing connects the two bottom as well as the two top chords.
The bridge deck is located between the two bottom chords and consists of several layers of vertical, horizontal and diagonal timber bracing. This massive construction was necessary to support the weight of loaded trains.
The entire structure is covered with a shallow pitched gable roof. The roof is framed with light gauge rafters extending from the top chords to the ridge pole. The roof structure is reinforced at regular intervals with a timber king post truss. These trusses are further supported by the upper lateral braces which intersect beneath each king post.
A very unusual roof reinforcing truss is located directly behind each of the two portals. It consists of a conventional king post roof truss supported by a small timber lattice truss. The bottom chord of the lattice truss is supported at either side by two wood ship's knees. Similar trusses were used in the roof of the St. Albans' train shed (1869).
The portals are sheathed with narrow horizontal flush board siding. The portal openings are rectangular. The flared eaves of the portals are semi-circular. Vertical board sheathing, which protects the exposed main trusses from the weather, extends approximately 15 feet inside each portal.
On the exterior, the sides of the bridge formed by the main trusses are sheathed with flush laid planks. A small space was left between each plank. This sheathing flares out at the bottom of each side to form a continuous protective apron over the lower chords. A long rectangular smoke escape slot, located near the roof eaves of each side, extends almost the full length of the structure.
An abutment underlies the bridge at either end and the central spans are supported by two evenly spaced piers. Both the piers and the abutments are constructed of rusticated granite blocks.
Major structural joints in the bridge are both pegged and bolted.
North elevation (1973)
Detail of main truss (1973)
