TR-245 Bridge

Information and Findings From Ohio's Historic Bridge Inventory

Setting/Context

The bridge is abandoned and closed to traffic. It is in a rural setting of active agriculture.

Physical Description

The 1 span, pin-connected Pratt pony truss bridge has built-up compression members and eyebar or rod tension members. The upper chords are toe-out channels with cover plates and battens. The verticals are angles with lacing. The diagonal rods connections at the upper chord connection in the end panels is bolted through a cast-iron connecting piece, a detail associated with the Wrought Iron Bridge Co. The floorbeams are suspended from the lower chord pins by U-shaped hangers. The wood deck is partially missing. The bridge is supported on stone abutments.

Integrity

The bridge has significant impact damage that has opened/twisted the end posts on the south side. Cover plates are missing and or holed through. The ashlar abutments are cracked and failing.

Summary of Significance

The ca. 1880 pin-connected Pratt pony truss bridge has lost integrity of design due to impact damage and metal-related deterioration. It is 1 of at least 13 examples of pony trusses by this builder and of similar date/design in the ODOT inventory (July 2009). The more complete examples better represent the technological significance of the type/design.

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design of the last quarter of the 19th century and continued to be built into the 20th century, although eventually superseded in popularity by Warren trusses.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