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River Road Bridge

Opie Road Bridge

   


River Road Bridge

Primary Photographer(s): Nathan Holth and Rick McOmber

Bridge Documented: July 11, 2008
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Key Facts

Facility Carried / Feature Intersected
River Road (Opie Road) Over South Branch Raritan River
Location
Rural: Somerset County, New Jersey
Construction Date and Builder / Engineer
1921 By Builder/Contractor: Dover Boiler Works of Dover, New Jersey

Technical Facts

Rehabilitation Date
2006
Main Span Length
89 Feet (27.1 Meters)
Structure Length
180 Feet (54.9 Meters)
Roadway Width
28 Feet (8.5 Meters)
Spans
2 Main Span(s)
NBI Number
18C0607

Historic Significance Rating (HSR)

Bridge Documentation

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

Because of the design of metal truss bridges, it is generally not possible to widen the truss bridge without rendering the trusses themselves decorative. Usually projects to widen historic truss bridges involve building a new stringer bridge and placing the trusses on top of the stringer bridge for decoration. This bridge was widened in 2005-2006. It brought the width of the bridge from 18.2 Feet (5.5 Meters) prior to widening to 28 Feet (8.5 Meters). This project was unique in that the bridge is still functioning as a truss bridge. As one might imagine, much of the original bridge material has been lost, although the truss web contains a significant amount of original bridge material. On this bridge, the floorbeams are new, and extremely large amounts of strengthening were bolted into the original truss metal, and many rivets replaced with bolts to allow the truss webs to support a much larger deck than the bridge was designed for originally.

This solution is unique because while the truss webs were perhaps more altered than when trusses are placed decoratively on a wider stringer bridge, this form of truss widening retains original bridge truss function, at the sacrifice of historic integrity of the truss web.

Whether the trusses function or not, the downside to this is that is critically alters the historic integrity of the bridge, and the incorrect width dimensions tend to make the bridge look fake to anyone familiar with historic truss bridges.

Information and Findings From New Jersey's Historic Bridge Inventory

Discussion of Bridge (Prior To Alteration)

Summary: The two-span, six-panel, riveted Pratt pony truss bridge has concrete abutments and cutwater pier. The bridge is one of the least altered of over 15 pony trusses built between ca. 1900 and 1927, and it is the only rivet-connected Pratt pony truss in the county. It is a well preserved example of a historically and technologically significant type that is becoming increasingly rare in the state. The riveted Pratt is not a common 20th-century pony truss type, which adds to the value of the span.

Physical Description: The 180'-long bridge consists of two six-panel half-hip Pratt pony trusses of equal length. The trusses are rivet connected rolled steel sections. The upper chords and inclined end posts are built-up box beams with cover plates. The lower chords, verticals, and diagonals are angles with lacing. In addition, the bridge has angle outriggers. The floor beams and stringers are I-beams. The abutments and cutwater pier are concrete. The bridge is well-preserved, and has not been significantly altered. The lower panel points and floor beam hangers have been repaired with bolts. A modern beam guide rail has been added.

Historical and Technological Significance: The Opie Road Bridge is one of the least altered of over 15 pony trusses remaining in the county from between ca.1900 and 1940. While this is the example that is a riveted Pratt pony truss bridge, it is a late example of riveted pony truss bridge technology, and it exhibits no unusual or noteworthy construction details. The Pratt truss bridge type was patented in 1844 by Thomas and Caleb Pratt of Boston, but did not gain popularity until the last half of the 19th century when it became one of the most common American truss types. Many engineers favored the Pratt truss type because of its easily determined structural action, simplicity and economy of metal. Others, like the opinionated J. A. L. Waddell, recommended its use for thru trusses, but did not recommend its use for pony trusses because of the lack of upper lateral support of the top chord. The perfection of riveted field connections brought the ascendancy of the Warren truss for pony truss spans after the turn of the century, and they are much more common than 20th century riveted Pratt trusses. This span is technologically significant because of it is an uncommon example of a rivet connect Pratt pony truss span. It is also well preserved (criterion C). No local records have been located to determine the builder or engineer for the Opie Road Bridge.

Boundary Description and Justification: The bridge is evaluated as individually significant. The boundary is limited to the span itself, including the substructure.

Discussion of Surrounding Area

The narrow two-lane bridge spans a wide section of the river in the western part of the county. The area is rural with fields, pastures, and a farmhouse (c. 1820) to the west. A housing development (c. 1990) is being built to the east, but out of sight of the bridge.

Bridge Considered Historic By Survey: Yes

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Photos and Videos: River Road Bridge

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