Little Yellow Creek Private Bridge

Information and Findings From Ohio's Historic Bridge Inventory

Setting/Context

The bridge carries a private farm lane over a stream in a setting of active farms.

Physical Description

The lightly built, 1-span, pin-connected Pratt pony truss bridge is supported on stone abutments. The upper chords are built-up of toe-out channels with cover plate and battens. There are cast-iron connecting pieces at the end posts. The diagonals in the end panels pass through the upper chord and are bolt connected at the connecting pieces. The center-panel vertical is built-up of angles with battens, but the verticals (floorbeam hangers) in the end panels are four rods that pass through the flanges of the built-up floorbeams, which are hung below the lower chord. The lower chord eyebars bypass the end panel hangers and are held in place by cast-iron guides.

Integrity

Very heavily rusted.

Summary of Significance

The pin-connected pony truss bridge, which is dated ca. 1878 based on style, is technologically significant due to its age and non-standard details, particularly the connection details at the upper chords-end posts and the end panel hangers (Criterion C). The bridge is tentatively attributed to the Wrought Iron Bridge Co. (WIBCo) based on the connection details, but these details differ slightly from the larger connecting pieces and built-up hangers found with other documented examples in the study. The design is described as "very popular" and having been built widely in an 1881 WIBCo catalogue. It is 1 of 13 very similar examples dating from 1874 to the early 1890s.

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design of the last quarter of the 19th century and continued to be built into the 20th century, although eventually superseded in popularity by Warren trusses.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

Justification

The bridge is one of over 150 extant pin-connected truss bridges dating from 1874 for pony trusses and 1876 for thru trusses. Twenty six predate 1888 and represent the era of experimentation that evolved into standardized designs by about 1888. This example has moderate significance because the genre and the fabricator are so well represented in Ohio.

Bridge Considered Historic By Survey: Yes