Ketterman 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 wooded rural setting. There is a modern house beyond one quadrant.

Physical Description

The 1-span, 52'-long, rivet-connected, Pratt pony truss bridge is supported on concrete abutments. The bridge's members are built-up with toe-out channels with cover plate and battens for the upper chords. The verticals were originally two pairs of angles, but these have been truncated/altered at about mid-height and strengthened by the addition of welded channels that continue downward to pick up the floorbeams by welded connections, replacing the original riveted connections. Some rivets have also been replaced at the lower panel gusset plates. The lower chords and diagonals are paired channels with battens. At the ends of the truss, plate has been welded to the lower chords and end-post cover plates as a strengthening measure. The bridge has rolled floorbeams, stringers, and a timber deck. The floorbeams have been strengthened by the addition of welded channels to the lower flanges at the ends of the beams. Riveted lattice railings are placed inside the truss lines. There is no builder's plaque.

Integrity

The integrity of original design has been compromised by the alterations to the riveted connections at the lower panel points, including replacement of rivets with bolts and welded connections. Many members (verticals, end posts, lower chords, and floorbeams) have irreversible welded repairs and the addition of plate. The welded repairs appear to post-date the prior ODOT truss survey photos (ca. 1980).

Summary of Significance

The rivet-connected Pratt pony truss dates ca. 1915 by style but the builder is not documented by available county records. It has alterations that have impacted the integrity of original design, significantly impacting the appearance and function of the truss connections. More complete and documented examples of riveted-connected trusses of similar age and design have been identified and better represent the significance of the truss type to the development of Ohio's highway systems. The not eligible recommendation of the prior inventory remains appropriate.

Pratt trusses were undoubtedly the most popular truss design of the last quarter of the 19th century and continued to be built into the 20th century, although eventually superseded in popularity by Warren trusses. The design, which initially was a combination of wood compression and iron tension members, was patented in 1844 by Thomas & Caleb Pratt. Ohio has three covered bridges that use this combination configuration, but they are all modern reconstructions based on the Pratt patent. The great advantage of the Pratt over other designs was the relative ease of calculating the distribution of stresses. More significantly, it translated well into an all-metal design in lengths of less than 200'. Significant surviving examples of all-metal Pratt trusses mostly date to the last quarter of the 19th century, and they are found with thru, pony, and the less common bedstead configuration. Prior to about 1890, a variety of panel point connections were in widespread use (including bolts, cast-iron pieces, and pins), but engineering opinion was coalescing around pins as the most efficient and constructible. Many of the connection details were proprietary and associated with individual builders or companies, and thus earlier examples are generally taken to be technologically significant in showing the evolution of the design. Later post-1890 Pratt trusses show a progression toward less variation in their details such that by 1900 the design was quite formulaic with few significant differences between the designs of various builders. This marked the end of the pin-connected Pratt's technological evolution and, in fact, it was soon waning and eclipsed in the highway bridge market by more rigid, rivet-connected truss designs, particularly the Warren but also riveted Pratts. The transition to riveted connections, which happened even earlier with railroads than highways, was in no small part due to concerns about stress reversals at the pins under heavier loads and improvements in pneumatic field riveting equipment in the early 1900s. In Ohio, Pratt truss highway bridges, whether pinned or riveted, were almost always built under the auspices of counties and local units of government; the Pratt was not a standard design of the state highway department.

In Ohio, there are 185 Pratt trusses dating from ca. 1874 to 1945 with at least 60 dating prior to 1900 (Phase 1A, 2008). The technologically significant unaltered examples of pin-connected Pratt trusses for the most part date prior to 1900 and have documented or attributed builders and dates of construction and/or significant connection or member details. Later post-1900 examples are less technologically significant. Significant unaltered examples of riveted-connected Pratt trusses date from ca. 1900 to 1915.

Bridge Considered Historic By Survey: No