With metal truss bridges, sometimes good things come in small
packages, and such is the case with this little driveway bridge. This is a very
short four panel pin connected Pratt truss bridge with counter diagonals in each panel.
This bridge has the appearance of a very old bridge because of its unusual, non-standard details and its lightweight construction. The top chord connections at the hip vertical have a threaded rod with nut connection type with cast iron
fittings in this area as well. This is similar to a design the Wrought Iron Bridge Company used on many of its pony trusses. However, the exact design of the castings as well as the fact that the hip vertical in addition to the diagonal
member has the threaded rod with nut detail is unlike the usual Wrought Iron Bridge Company design. This, combined with other unusual detail unlike most Wrought Iron Bridge Company bridges leave it questionable at best that the Wrought Iron
Bridge Company built this bridge. The vertical
member in the center of the bridge is built up unusually, with a single lattice
element in the center, and battens on the rest of it.
This bridge is on a private drive, but is right next to the public road, and you
can easily view the bridge and shoot photos from the road. Hopefully whoever owns this bridge realizes what a treasure they have.
Information and Findings From Ohio's Historic Bridge
The bridge carries a private farm lane over a stream in a setting of
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.
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.
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
Photo Galleries and Videos: Little Yellow Creek Private Bridge
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Maps and Links: Little Yellow Creek Private Bridge
This bridge is on a private drive, but is right next to the public road.