TR-84 Bridge

Information and Findings From Ohio's Historic Bridge Inventory

Setting/Context

The bridge is closed to traffic. It is on a 2 lane road over a stream in a sparsely developed, rural setting.

Physical Description

The 1 span, 64'-long, pin-connected Pratt pony truss bridge is traditionally composed of built-up compression members and eye bar tension members. It is supported on stone abutments.

Integrity

Railings replaced (ca. 1970). Vertical replaced with rolled section (ca. 1970).

Summary of Significance

The ca. 1885 pin-connected Pratt pony truss bridge built by the Wrought Iron Bridge Co. has no unusual or distinctive features. WIBC was a prolific building prior to 1901, and more complete examples exist in the state. This is a later example of the company's work and does not have the distinguishing details of many of the earlier examples. There has been no change in the bridge's status since the prior inventory. The not eligible recommendation of the prior inventory remains appropriate. One vertical has been replaced with rolled section. The company built the same basic bridge from at least 1874 into the 1890s. This is one of 13 similar examples in the state.

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design of the last quarter of the 19th century and continued to be built into the 20th century, although eventually superseded in popularity by Warren trusses.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