Built in 1902, this is a classic six panel pin connected Pratt
through truss. Two rows of channel form the original or old guardrails that
remain on the bridge. There is v-lacing under the built-up top chord and on the built-up vertical
members. Some idiot must have driven across the bridge with too tall a load and
they knocked out the bottom section of the a-frame portal bracing.
Unsurprisingly, the county posted a clearance sign above the bridge. It is unknown if the sign was posted before, or if the county only did it only after the damage had
been done. The only other significant alteration noted with this bridge is
the addition of an extra rolled i-beam under the floor beams. The deck of the bridge is
wooden with an asphalt wearing surface. The bridge sits on stone abutments.
As of 2012, there have been rumors going around that Preble County may rehabilitate this bridge. HistoricBridges.org sincerely hopes that these rumors are true, since far too many of the county's historic truss bridges have been
demolished since HistoricBridges.org documented the county in 2006.
Information and Findings From Ohio's Historic Bridge
The bridge carries a 2 lane road over a stream in a rural area of active farms.
The 1 span, 93'-long, pin-connected Pratt thru truss bridge is conventionally composed of built-up compression members and eyebar tension members.
Summary of Significance
The 1902 pin-connected Pratt thru truss bridge is later example of a common type/design and has no distinctive details or features. The builder is not documented by available county records. The not eligible
recommendation of the prior inventory remains appropriate.
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eventually superseded in popularity by Warren trusses.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.
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