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Indian Mill Bridge

Indian Mill Bridge

Primary Photographer(s): Rick McOmber

Bridge Documented: May 19, 2006 and June 25, 2011

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Key Facts

Facility Carried / Feature Intersected
CR-47 Over Sandusky River
Location
Rural: Wyandot County, Ohio: United States
Construction Date and Builder / Engineer
1913 By Builder/Contractor: Modern Construction Company of Fremont, Ohio

Technical Facts

Rehabilitation Date
Not Available or Not Applicable
Main Span Length
172 Feet (52.43 Meters)
Structure Length
178.2 Feet (54.32 Meters)
Roadway Width
17 Feet (5.18 Meters)
Spans
1 Main Span(s)
NBI Number
8835764

Historic Significance Rating (HSR)

Bridge Documentation

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

Ohio has a number of similar truss bridges that are quite unusual. They are unusual because they were built in the 1910s, yet feature the ornate details and builder plaques that would be expected of bridges found in the late 1800s. The only indication that these bridges are from a later period are the different contractors shown on the plaques, while the design of the bridge, apparently a standard plan, remains the same. Cambria mill marks are present on the bridge. V-lacing is present on the verticals and sway bracing, as well as under the top chord and end post. Original lattice railings remain. Ornate sunburst designs are present on top of the a-frame portal bracing. There are also decorative finials on top of the end posts. The bridge is in decent condition. Historic integrity is slightly decreased due to extensive and sloppy steel patching and welding on various parts of the bridge. This is quite noticeable on the bottom chord. Still, the bridge remains as a beautiful bridge and is more than worthy of preservation. It is significant for its location as well, next to a mill. The scene of a mill with a truss bridge crossing the river nearby is a historic scene that would have been very common in the turn of the 20th century but is today very rare to see both the mill and bridge remaining.

The historic bridge inventory states that the builder is not documented by available county records. How could they miss the giant plaque on the bridge stating who built the bridge?!

Information and Findings From Ohio's Historic Bridge Inventory

Setting/Context

The bridge is adjacent to the National Register-listed Indian Mill State Memorial. It carries a one lane road over the river in a wooded setting that includes an early 20th century house and a park. The mill has a period of significance from 1850-1874, so the bridge was built outside the period of significance.

Physical Description

The pin connected Pratt thru truss bridge is traditionally composed, although pin plates are used at the lower panel point. It is an extremely late example of its type, but its cresting and other ornamentation survives. Flooring system was rehabilitated. Posted.

Integrity

Has integrity.

Summary of Significance

The 1913 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. It was built after the period of significance of the mill, and it is a very late example of its design.

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.

Bridge Considered Historic By Survey: No

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