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St. Clair Street Bridge

St. Clair Street Bridge

Primary Photographer(s): Nathan Holth

Bridge Documented: May 7, 2006

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Facility Carried / Feature Intersected
St. Clair Street Over 7 Mile Creek
Eaton: Preble County, Ohio: United States
Construction Date and Builder / Engineer
1887 By Builder/Contractor: Columbia Bridge Works of Dayton, Ohio
Rehabilitation Date
Main Span Length
100.0 Feet (30.5 Meters)
Structure Length
108.0 Feet (32.9 Meters)
Roadway Width
15.7 Feet (4.79 Meters)
1 Main Span(s)
Inventory Number

Historic Significance Rating (HSR)
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Bridge Documentation

View Archived National Bridge Inventory Report - Has Additional Details and Evaluation

This bridge is one of the most spectacular historic bridges in southwestern Ohio. It is an eight panel pin connected Pratt through truss. It was built in 1887 by the Columbia Bridge Works, of Dayton Ohio. The bridge is noted for its outstanding historic integrity, in particular its retention of all ornamental elements including builder and commissioner plaques, as well as decorative finials. The bridge even sits on handsome stone abutments, which have a stone on top that has a date and engineer engraved into it. The bridge is also a noteworthy example of a bridge built by the Columbia Bridge Works. It stands out among bridges built by this company because the bridge is traditionally composed, with built-up beams containing v-lacing and battens, as well as traditional eyebars for diagonals and the bottom chord. Bridges built by Columbia Bridge Works usually are not traditionally composed and instead display unusual connection details, as well as an unusually heavy use of rolled beams instead of the built-up beams that were more common during that period. It is unknown why this bridge does not display the typical Columbia Bridge Works details. The ornamental features of this bridge are, in contrast, very much in line with typical Columbia Bridge Works design, from the finials that include the construction date at the base to the fancy arch-shaped builder plaque.

The only truss alteration noted on the bridge was minor, the replacement of a turnbuckle. The bridge's current deck is somewhat unusual, but attractive looking, a timber deck with red brick wearing surface.

The St. Clair Street Bridge has stood in the same place for well over a century and to this day continues to perform its original function. The good condition of the trusses demonstrates how long-lived the pin connected truss bridge could be if properly maintained, and suggests how much longer it can remain the crowning Eaton landmark for another century if Preble County chooses to continue to maintain it.

It is hoped that Preble County will indeed choose to preserve this historic bridge. Preble County, like much of the United States has shown an almost feverish obsession with preserving and promoting its wooden covered bridges. Historic metal truss bridges on the other hand have been neglected, demolished, and replaced. Only in a couple instances has Preble County shown a commitment to preserving its metal truss bridges. The time to increase the county's portfolio of preserved metal truss bridges is now (before it is too late), and this bridge should be among those preserved. Especially given that a short distance from this bridge crossing the same creek is a preserved covered bridge, to do anything other than preserve this bridge would only be a blatant continuation of the nationwide discrimination that metal truss bridges receive when compared to preservation of covered bridges. Further, this bridge is a great opportunity to try to draw attention to historic metal truss bridges. Even the many people who believe the only type of historic bridge is a covered bridge might take notice of this strikingly beautiful, well-ornamented historic metal truss bridge. Some people seem to think metal truss bridges are industrial looking or are utilitarian in appearance. Nothing could be further from the truth, when considering this particular bridge. This bridge is a great bridge to introduce people to the beauty of historic truss bridges.

The St. Clair Street Bridge is the only Preble County bridge that is listed on the National Register of Historic Places. In contrast, every one of the wooden covered bridges extant in the county is on the National Register. Many of the county's metal truss bridges should be listed as well. Instead, many of Preble County's metal truss bridges instead are on the demolition list or have already been demolished, since HistoricBridges.org's 2006 documentation of the county.

Information and Findings From Ohio's Historic Bridge Inventory


The bridge carries a 2 lane street over a stream in a residential setting in Eaton. There is a park beyond one end of the bridge.

Physical Description

The 1-span, 108'-long, pin-connected Pratt thru truss bridge is traditionally composed of built-up compression members and eyebar tension members. It has decorative portal bracing with brackets, finials, and builders plaque. There are lattice railings. The bridge is supported on stone abutments.

Summary of Significance

The pin-connected Pratt thru truss bridge was fabricated by the Columbia Bridge Works, a prominent Ohio fabricator, in 1887. It is a classic example of its type/design. It is NR listed (1978).

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


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Maps and Links: St. Clair Street Bridge

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Bridgehunter.com: View listed bridges within 0.5 miles (0.8 kilometers) of this bridge.

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HistoricBridges.org Bridge Browser: View listed bridges within 10 miles (16 kilometers) of this bridge.

2021 National Bridge Inventory: View listed bridges within 0.5 miles (0.8 kilometers) of this bridge.

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