This bridge is one of the most unusual bridges in Ohio, and it
has a very high level of historic significance due to its rare design. The
bridge is in overall design a traditional pin-connected Pratt through truss, and
with an 1883 construction date, is significant as an early example. However, it
is a three span continuous bridge, making it an extremely early and highly unusual example of a
continuous truss bridge. It is also rare as an example of a pin-connected Pratt
truss bridge that is continuous. The pin-connected Pratt truss bridges which
became a traditional standard and were built across the country during the last
two decades of the 1800s were nearly always built as simple spans. The Old Zoar
Bridge is a noteworthy deviation from this. It is unclear why the Wrought Iron
Bridge Company built this bridge as a continuous structure.
Fortunately, the future of this historic bridge appears
secure. The bridge has been preserved and is now in use as a non-motorized
The bridge has lattice sway bracing where each span meets, and
on these sections, if you look closely, you can see that some of the lattice is
made of angles, and where they were, they were bent and flattened at the ends to
fit in between back-to-back angles. This is an interesting detail to note.
Overall, the preservation of this bridge appears to have been
executed in an acceptable manner. However, there is one issue to note in the
hope that future bridge preservation projects will not repeat a serious error.
Original railings do not remain on the bridge. The most problematic issue with
the quality of the preservation of this bridge is the current railings which are
thick wooden boards. This type of railing has been a serious problem because so
many truss bridges use this in a preservation project. This should be considered
an unacceptable installation because there are numerous alternatives that
provide a reasonable amount of safety while also not obstructing the view of the
Information and Findings From Ohio's Historic Bridge
Access bridge from Eberhart Rd NW.
The 3 span, pin-connected Pratt thru truss bridge has built-up compression members and eyebar or rod tension members. It has the cast connecting pieces at the upper chord-end posts connections through which to
thread the diagonals, so typical of Wrought Iron Bridge Co. bridges of this period. There are lattice portal bracing with lattice brackets and builders plaques. The available photo appears to show the truss to be continuous over the
piers, a very unusual practice for 1883.
Summary of Significance
The 1883 pin-connected Pratt thru truss bridge on old CR 82 was bypassed prior to 1976. Although there was some threat of removing the bridge in the mid 1980s, it was eventually rehabilitated for use as part of
the Zoar Valley Trail in 2004. It is a very technologically significant example of its type/design with details associated with the Wrought Iron Bridge Co., a prominent Ohio fabricator. The 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.
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
This bridge is tagged with the following special condition(s): Reused and Unorganized Photos
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