Mill Road Bridge

Information and Findings From Ohio's Historic Bridge Inventory

Setting/Context

The bridge carries a 1 lane road over a stream in a rural setting. At the southeast quadrant is a 1.5-story frame building with sheet-metal gambrel roof; a sign identifies it as "Giant Oak Mill, est. 1803." A period farmhouse is beyond the southeast quadrant. Another period farm complex is beyond the northeast quadrant. At the northwest end of the bridge is a T-shaped intersection.

Physical Description

The 1 span, 131'-long, pin-connected, eight-panel, Camelback thru truss bridge is traditionally composed with built-up compression members and eyebar tension members. The upper chords are toe-out channels with cover plate and battens. The verticals are toe-out channels with lacing. The lower chords and diagonals are eyebars. The upper-lateral braces are T-sections with rod crossbracing. The portal bracing is non-original welded channel sections. The floorbeams are suspended from the lower panel points by U-shaped hangers. The floorbeams carry steel stringers and a wood deck. The bridge is supported on concrete abutments.

Integrity

Deck and original lattice railings replaced in 1994. Lower-chord eyebars, end-panel floorbeam hangers, and diagonals irreversibly altered by welded repairs and welded strengthening at the lower panel points. Portal bracing replaced with welded channels.

Summary of Significance

The Camelback thru truss bridge dates ca. 1905 by style but is reported as built in 1932 by county records, which probably indicates the bridge was relocated here in 1932. The bridge has no unusual or technologically distinguishing features for an early 20th century, pin-connected truss. Its integrity of design has been significantly compromised by the welded repairs to the lower panel points. These repairs are irreversible and have changed the way the truss functions at the pin connections. More complete and distinguished examples of this type/design better represent the significance of the technology.

Camelback trusses are a member of the Pratt-family of trusses with a top chord of exactly five slopes. Technologically, they are no different than Parker trusses, differing only in the number of slopes (Parkers have more than five slopes.) They thus share the same context, which is that less material is needed in their construction as compared to a parallel chord truss of similar span. The sloped-chord trusses provided the greatest depth at midspan where it is needed to accommodate the stresses. The practice of sloping the top chords of wood trusses dates to at least the 1840s and appeared in the development of metal trusses at least as early as the 1870s. Pin-connected Camelback and Parker trusses were used primarily before 1910 for long-span crossings where the economy of material had the greatest effect, and rivet-connected examples were particularly popular as standard designs of some state highway departments in the 1910s to 1940s, also for similar economic reasons. The Ohio State Highway Department used Camelback and Parker trusses with documented examples dating to the 1920s to 1940s.

Bridge Considered Historic By Survey: No