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Clay Road Bridge
Primary Photographer(s): Nathan Holth
Bridge Documented: June 30, 2006
Rural: Ashtabula County, Ohio: United States
Not Available or Not Applicable
Main Span Length
47 Feet (14 Meters)
50 Feet (15 Meters)
16 Feet (4.88 Meters)
1 Main Span(s)
This is a small Warren pony truss, that retains a high degree
of historic integrity. The bridge retains original pole railings. The builder
plaque remains on the bridge, crediting the Brookville Bridge Company with
building the bridge in 1919. The deck is concrete. Connections on the bridge are
riveted. Extensive v-lacing is on the bridge, present under the top chord / end
posts, and on the verticals and diagonals. Steel on the bridge was fabricated by
Information and Findings From Ohio's Historic Bridge
The bridge carries a 1 lane road over a stream in a sparsely developed, rural setting.
The 1 span, 50'-long rivet-connected Pratt pony truss bridge is composed of built-up members and has pipe railings.
Summary of Significance
The 1919 Pratt pony truss is a late example of its type/design with no distinguishing features. It has riveted connections, typical of Pratt trusses from about 1900 to the 1940s when riveted connections began to
be phased out in favor of welded connections. This example is not historically significant for its technology or context. More distinguished examples better represent the significance of the type/design in the development of the
state's road systems.
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design of the last quarter of the 19th century and continued to be built into the 20th century, although eventually superseded in popularity by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
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