Bridge Description Shoreham Covered Railroad Bridge, Shoreham Vermont
The Shoreham Railroad Bridge is a single-span wooden Howe truss covered bridge. The total length of the bridge is 109 feet, with a clear span of 94'-6". The truss is 21'-0" high from the top of the upper chord to the bottom of the lower chord and 19'-4" wide out to out, with a width of 14 feet between the trusses.
Each ten-panel truss is framed in the manner patented by William Howe in 1840. The upper chord is four lines of 6"x10" timbers with shear blocks, bolted together. The lower chord is four lines of 6"x12" timbers with shear blocks, bolted together. The chords are connected by vertical endposts, paired diagonal 7"x9" timbers, 6"x6" counter diagonals and groups of vertical iron tension rods, varying in number and dimension (from two to six in each group and from 1½" to 2½" in diameter). The number of rods increases toward the ends of the trusses: panels 4, 5, 6 and 7 have three 1½ diameter rods; panels 3 and 8 have four rods (two 1½ diameter and two 1¾" diameter); panels 2 and 9 have six rods (four V½" diameter and two 1¾" diameter); and panels 1 and 10 have five rods (one 1½" diameter, two 1¾" diameter and two 2½" diameter). Panels 1, 2, 3, 8, 9 and 10 also have a third timber between the paired diagonals and two 3"x7" timbers with the counter diagonals. The upper and lower connections at each panel point incorporate triangular cast iron bearing block assemblies, with seats for the diagonal timbers and openings for the metal rods to pass through. Each rod passes through this assembly and through the chord, where it is fastened on the far side with a plate and nut. Some of the diagonal wood members of the trusses have been reinforced with additional timbers. Some of the rods appear to have been added after the original construction.
The floor system is composed of 7"x13" transverse floor beams spaced 2'-0" apart on top of the lower chord. There are two lines of stringers, each composed of a 6"x12" and a 10"x12" timber laid longitudinally on top of the floor beams, along the line of the former rails. The stringers carry transverse railroad ties, and originally, the railroad tracks, which have now been removed and replaced with a wooden walkway.
The upper lateral system is composed of 8"x8" transverse struts resting on the upper chord at each panel point and 6"x6" lateral diagonal bracing between the struts. This system appears to have been raised at some point for additional clearance. There are wooden sway braces between the struts and truss diagonals. Wooden rafters frame onto a longitudinal timber supported on the outer ends of the struts at the eaves. The gable roof is covered with wood shingles fastened to sheathing on top of the rafters.
The exterior of the bridge is covered with vertical board sheathing to the eaves. The sheathing is fastened to wooden nailers on the exterior faces of the trusses. The portals have elliptical arched openings, 13'-6" high. There are suggested capitals on the outer faces of the end posts. There are three 2'-6"x5'-0" window openings each side of the bridge; these are not original, but were added during the 1983 restoration.
The abutments are squared, drylaid stone masonry. The east abutment has a concrete cap; the west abutment is faced with concrete. The lower chords rest on two 8"x10" timbers and one 4"x10" timber on top of the abutment facewalls.