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7 Mile Road Bridge

7 Mile Road Bridge

Primary Photographer(s): Nathan Holth

Bridge Documented: May 7, 2006

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Key Facts

Facility Carried / Feature Intersected
7 Mile Road Over 7 Mile Creek
Location
Rural: Preble County, Ohio: United States
Construction Date and Builder / Engineer
1906 By Builder/Contractor: Indiana Bridge Company of Muncie, Indiana

Technical Facts

Rehabilitation Date
1985
Main Span Length
146 Feet (44.5 Meters)
Structure Length
155 Feet (47.24 Meters)
Roadway Width
15.7 Feet (4.79 Meters)
Spans
1 Main Span(s)
NBI Number
6831826

Historic Significance Rating (HSR)

Bridge Documentation

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

This bridge is one of only a couple surviving examples nationwide of a bridge design built by the Indiana Bridge Company of Muncie, Indiana and marketed as a High Triangular truss. The other is in Indiana. The truss design is unique, not copied by any other known company. It is essentially a pin-connected Polygonal Warren truss. Polygonal Warren truss bridges are otherwise limited to riveted connections among known surviving simple span truss bridges. The design of this bridge is similar, but not exactly the same as the patented Pegram truss bridge type. Indiana did additional research on the truss and found that in terms of engineering it functions differently than a true Pegram truss. In any case, as a rare surviving example of a highly unusual truss type, this bridge should receive the highest preservation priority.

A drawing from a "High Triangular" truss is shown to the right.

Cambria brands were found on the metal of this bridge. The bridge features pinned connections and is composed of six panels. The deck is wooden with an asphalt wearing surface. Original lattice railings remain on the bridge. The bridge's built-up beams include v-lacing, including some diagonal members that are are unusual box members with v-lacing on all four sides, an unusual detail that gives the members and open, lightweight appearance.

Information and Findings From Ohio's Historic Bridge Inventory

Setting/Context

The bridge carries a 2 lane road over a stream in a rural setting of active agriculture. There are fields to the bridge's east. To the west is a rail line carried over Seven Mile Road by an overpass with a 9'6" vertical clearance. The bridge's western approach roadway is a sharp S-curve.

Physical Description

The 1-span, 155'-long, pin-connected Pegram thru truss bridge is composed of built-up compression members and eyebar tension members. The upper chords are toe-out channels with cover plate and lacing. The compression members in the web are toe-out channels with lacing. The tension members in the web and the lower chords are eyebars. The upper laterals are angles with lacing. The bridge has A-frame portals with builders plaques. The plaques read, "1906, Indianapolis Bridge Co., Muncie, Ind., S. C. Richie, Isaac Ulrich, J. E. Flora, Commissioners." There are original lattice railings. The floorbeam hangers are pin plates from the web members; the hangers do not connect to the lower chords, a characteristic of the Pegram design. There are rolled floorbeams, rolled stringers (with channel fasciae beams), and a wood deck. The bridge is supported on concrete abutments.

Integrity

Deck replaced, 1985. Welded stiffeners have been added at the floorbeam hangers.

Summary of Significance

The 1906 Pegram truss is a rare type/design in Ohio that is technologically significant (Criterion C). There has been no change in the bridge's status since the prior inventory. The eligible recommendation remains appropriate.

This is Ohio's only identified example of a design that was patented by George H. Pegram (1855-1937) in 1885. The truss, which is characterized by the equal-length sloping upper chords, no verticals, and steeply sloped diagonals (60-75 degrees) was designed to economize on the amount of steel being used and allow for ease of disassembly and re-use. Pegram worked for the Missouri Pacific and Union Pacific RRs, and the design gained popularity in the Midwest and Rocky Mt. regions where most surviving examples can be found today (e.g. Idaho had seven at latest report). The primary objection to the bridge type was the difficulty of making riveted connections, and it had largely fallen out of use by the 1910s.

Justification

The design is rare with this being the only example. It has exceptional significance.

Bridge Considered Historic By Survey: Yes

View PDF Historic Bridge Management Plan

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