In 2006, Preble County had a few bridges built by the
Brookville Bridge Company, all dating from the 20s or 30s. Another is the Foos Road Bridge. The Bower Road Bridge however
is the only through span in the county by this company; the others are pony truss bridges. Composed of built-up top chord and end post box beams, while vertical and diagonal members are rolled i-beams, this bridge has a somewhat plain
appearance compared to older truss bridges, but with riveted
connections and its location tucked away in the trees, this bridge still is a
charming structure. The only v-lacing present on this bridge is under the top
chord and endposts. The bridge is a Pratt truss with eight panels, and features
features a-frame portal bracing. There are rocker bearings present at the east
end of the bridge. The structure sits on concrete abutments. The deck stringers
appear to have been replaced, and when they were, they were mounted differently,
simply laid on top of the floorbeams, rather than riveted to the floor beam web.
A small beam bridge, which features riveted railings and stone abutments, is present a bit west of this bridge. It may have been built at the same time, perhaps by the same company.
Information and Findings From Ohio's Historic Bridge
The bridge carries a 2 lane road over a stream in a sparsely developed, rural setting.
The 1 span, 131'-long, rivet-connected Pratt thru truss bridge has rolled section web members and built-up chords. The portal bracing is an A-frame, and there are channel railings.
Summary of Significance
The 1931 rivet-connected Pratt thru truss is a late example of its type/design with no distinguishing features or details. The not eligible recommendation of the prior inventory remains appropriate.
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design of the last quarter of the 19th century and continued to be built into the 20th century, although eventually superseded in popularity by Warren trusses.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.
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.
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