Mount Vernon Bridge Company: Probable Builder
HistoricBridges.org strongly suspects this bridge to date to the late 1880s, and to be a product of the Mount Vernon Bridge Company of Mount Vernon, Ohio. This is NOT a proven or documented association, but appears to be very likely. Compare this bridge to the Martin Road Bridge and the Bennett Road Bridge, documented products of the Mount Vernon Bridge Company. All three of these bridges feature built-up floorbeams that are NOT a fishbelly design, but are simple rectangles, and also include riveted angles as little ribs on the sides of the beams. The Martin Road Bridge (the oldest known surviving work of the company) doesn't have any other similarities. The Bennett Road Bridge in contrast has several additional similarities. They both share the same very small, lightweight portal bracing design with a single row of lattice. Although the Bennett Road Bridge has the unusual detail of having no sway bracing or struts, Bennett and Warren Road Bridges share the same uncommon use of angle for the latteral bracing. Both bridges attach this lateral bracing to unusual gussett plates that stick out from the top chord. Lastly, both Bennett and Warren Road Bridge use a riveted pin plate to hang the floorbeam from the trusses, as opposed to a u-bolt. The use of riveted pin plates (instead of u-bolts) is somewhat uncommon in earlier Pratt trusses from the 1880s and early 1890s, and is more common in later examples. Yet the Warren Road Bridge, with its built-up floorbeams and lightweight truss members (and evident use of wrought iron instead of steel) looks more like an 1880s truss bridge. Further, the Bennett Road Bridge which which it shares details is also from the 1880s. Few companies in the 1880s used riveted pin plate hangers for their trusses. Therefore this detail lends strength to an argument that the Warren Road Bridge is a product of the Mount Vernon Bridge Company.
One final argument in favor of Mount Vernon Bridge Company being the builder of this bridge. This bridge is in the same county as the city of Mount Vernon... the bridge is not physically far from Mount Vernon.
None of the above observations on their own are very strong arguments in favor of proving that the Warren Road Bridge was built by Mount Vernon Bridge Company. There are no "dead-ringer" details on any products of the Mount Vernon Bridge Company that are proof positive as unique details associated with the company. Yet at the same time, combining all of the above observations together makes for a decent argument in favor of Mount Vernon. Adding to the argument is that no other prolific builders come to mind as using this combination of design details on their bridges.
Problems With Historic Bridge Inventory's Assessment
The assessment of this bridge by the Ohio Historic Bridge Inventory is extremely poor. It was oblivious to all the above arguments. Moreover , it describes a "lostt of original fabric from corrosion." Firstly, it is highly irregular to reduce a metal truss bridge's significance due to "corrosion" as this is a structural integrity concern not a historical integrity concern. "Corrosion" such as pack rust and section loss can be sensitively repaired to maintain historic integrity. Further, take a look at HistoricBridges.org's photos for this bridge. What corrosion is there?! There is none! The bridge is wrought iron and the rust is largely surface rust. The amount of pack rust and section loss on this bridge is at the very least best described as less than average for a bridge of this type.
Perhaps most remarkable is the ca. 1900 date that the inventory suggests. This bridge's extremely lightweight truss members, apparant use of wrought iron (due to lack of section loss on the unpainted metal), and use of built-up floor beams all are suggestive of a bridge that at least dates to the 1890s, but could very well date to the 1880s.
Because of these shortcomings, this bridge should be re-evaluated for historic significance. Even on the off-chance that it is a product of Mount Vernon Bridge Company, it should be considered historic. The Bennett Road Bridge discussed above is being demolished and replaced, so few examples of the company remain in Ohio.
Information and Findings From Ohio's Historic Bridge Inventory
The bridge carries a 1 lane road over a stream in a sparsely developed, rural setting.
The 1 span, 94'-long pin-connected Pratt thru truss bridge appears to be traditionally composed and lightly constructed of built-up compression members and eye bar or rod tension members. It has ashlar abutments.
Loss of original fabric from corrosion. Impacted rust at lower panel points.
Summary of Significance
The ca. 1900 pin-connected Pratt thru truss bridge has no distinctive details or features. The builder and year built are not documented by available county records. It has loss of original fabric. 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
Bridge Considered Historic By Survey: No
This bridge is closed with the deck and deck stringers removed.
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