Jackson Covered Bridge, Bloomingdale Indiana
With thirty covered bridges, the most of any county in the United States, Parke County, Indiana, is known as "The Covered Bridge Capital of the World." The majority of these are Burr arch trusses built by JJ. Daniels (1826-1916) or J.A. Britton (1839-1929). The continued survival of many of these structures is due in part to the enduring craftsmanship of the builders, in part to the county's rural heritage that spared many covered bridges from replacement, and in part to ongoing local preservation efforts and promotion of these bridges as tourist attractions. Since 1957, the Parke County Covered Bridge Festival has attracted thousands of tourists and covered bridge fans annually, giving the county added incentive to invest in preservation efforts.
The Jackson Bridge is the oldest and longest surviving example of the work of J.J. Daniels, a prolific Indiana bridge builder, who built nearly sixty covered bridges in Indiana between 1855 and 1900. With a span of 207', the Jackson Bridge is the third longest single-span covered bridge in the United States, and the longest single span covered bridge that still carries vehicular traffic.
The Jackson Bridge is a single-span Burr arch truss covered bridge on cut and dressed stone masonry abutments. The overall length of the bridge is 225' with a reported clear span of 200'. The truss is approximately 19' high from the bottom of the lower chord to the top of the upper chord, and 21' wide overall, with a 16' roadway.
The truss is framed as a multiple kingpost structure, with eighteen 11' wide panels and a 9' wide shelter panel at each end. The upper chord consists of three lines of timbers (that appears to be an 8"xl2" timber flanked by 8"x8" timbers), blocked and bolted together. The lower chord appears to be the same configuration as the upper chord, except with 10"xl2" timbers flanked by 8"xl2" timbers. The chords are connected by paired posts and braces bolted with 3/4"-diameter bolts. There are four endposts at each corner, except the northwest corner where there is a single metal endpost. The vertical posts are tapered timbers (7"x12" at their widest point), which are smaller at the top and bottom where diagonals notch into them. The diagonal braces are 7"x9" timbers angling up toward the center of the span. The diagonals are notched into the upper and lower ends of the posts. A pair of arches flanks each truss. The arches spring from new poured concrete seats on the abutments about 5' below the lower chord, rise 25' to the crown, and span 200'-5".
The deck system is composed of transverse 4"x11" floor beams seated on the lower chord at approximately every 3-1/2'. There are sixteen lines of 3"x5-1/2" stringers on top of the deck beams. Plank decking (approximately 2"x8"; varies) is laid transversely on the stringers. There are longitudinal running boards (each composed of five lines of 2"x8" boards) on top of the decking. The lower chords rest on bed timbers on the abutment seats.
The lateral bracing is composed of tie beams (appear to be 6"x12") seated on the upper chord at each panel point. There is 5"x5" X-bracing lateral bracing notched into the tie beams. A longitudinal timber supported on the outer ends of the tie beams supports the lower ends of the rafters. The 2"x4" rafters are spaced at approximately 2'. There is no ridge beam. The gable roof has exposed rafters and is covered with corrugated sheet metal fastened to purlins on the rafters. There is 4"x6" sway bracing crossing diagonally between the upper chords and the vertical posts.
The bridge is covered with clapboard sliding to about 2' below the eaves. The clapboards are fastened to 2"x3" vertical nailers, which are spaced approximately 2' apart and fastened to three 3"x4" longitudinal nailers on the outer faces of the trusses. There are five framed window openings (approximately 22"x32") on each side of the bridge. Some of the windows have hoods. The portals are straight with arched openings flanked by engaged pilasters. Decorative lettering over the portals reads "Jackson Bridge, J.J. Daniels Builder, 1861." A stone in the southwest abutment is engraved with the words: "Builder J.J. Daniels 1861."