Bridge Description Kidd's Mill Covered Bridge, Greenville Pennsylvania
Kidd's Mill Bridge is a single-span Smith truss covered bridge. The total length of the bridge is 122' with a clear span of 118'-6". The truss is 16'-6" high from the top of the upper chord to the bottom of the lower chord and 20'-0" wide overall, with a roadway width of 16'-6".
The upper chord and lower chords are composed of three parallel timbers (6"xl0" in the upper chord; 6"xl2" in the lower chord), bolted together with shear blocks between them. The chords are connected by vertical 7"x7" endposts and wooden diagonal tension members (7"x7" at centerspan, increasing to 7"x10" at the ends of the span) with wooden compression counter braces (7"x7" at centerspan, increasing to 7"x11" at the ends of the span) intersecting at opposing angles at mid-truss height the full length of the truss. The tension members pass through the chords and the compression members butt up against the tension members near their intersection with the chords. The web members are bolted together at their intersection with each other and with the chord members.
The floor system is composed of 2"x12" transverse wooden floor beams, spaced 1'-9" apart, seated on the lower chord. There is wooden lateral cross bracing (approximately 4"x4") between the lower chords and bridging between the floor beams. There are no stringers. Variable width plank flooring (2" thick) is laid diagonally on top of the floor beams, with running boards (two lines of four boards laid longitudinally) nailed on top. The ends of the lower chords are seated on bed timbers on top of the abutments.
The truss is braced overhead with tie beams (approx. 6"x8") seated on the upper chord at regular intervals. There are ten sets of lateral overhead cross-bracing along the length of the truss. The lower ends of the rafters are seated on blocks on the upper chord. Corrugated metal fastened to 2"x4" purlins spaced at 18" on top of the rafters covers the gable roof. There are sway braces between the end posts and the ridge.
Board and batten siding (l"xl2" boards and l"x3" battens) covers the exterior of the bridge to approximately 3' below the eaves. The sheathing is fastened to 3"x4" nailers attached to wood blocks on the outer faces of the trusses. The portals have square openings with clipped corners and angle forward over the approaches.
The abutments are built of dry laid, cut sandstone and appear to be original. Behind the abutments, stone wingwalls angle back along the inclined approaches to the bridge. The area around the bridge has been developed as a park with a picnic area and hiking trails. The approaches to the bridge have been barricaded, but the structure is accessible to bikes and pedestrians.
Robert Smith was born in 1833 in Miami County, Ohio. The son of a cabinetmaker, he learned carpentry as a young man. In his late twenties, Smith ran a woodworking machine shop and lumberyard in Tippecanoe City, Ohio, with his brother. Smith eventually turned his attention to bridges and, in 1867, received a patent for his version of a double-intersection Warren truss. He subsequently organized the Smith Bridge Company at Toledo. The company built Smith, Howe and Warren trusses, and Smith's business increased rapidly, from five bridges in 1867 to seventy-five bridges in 1869. In 1869, Smith received a second patent for roofing and lateral bracing systems.
The Smith truss was designed specifically to compete with iron by using timber as efficiently as possible, and for a decade it was highly successful. Historians estimate that several hundred Smith trusses were built in nine states, being most popular in Ohio, Indiana, California and Oregon. The cost-effectiveness of iron led to the abandonment of the Smith truss design in the 1880s, but Smith's company made the transition and continued to build bridges until 1891. Robert Smith died in 1898 at the age of 63.
