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Raven Rock Bridge

   
                  


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Bridge Documented: July 11, 2008
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Key Facts
Bridge Name Facility Carried / Feature Intersected Location Structure Type Construction Date and Builder/Engineer
Raven Rock Bridge
Raven Rock Road Over Lockatong Creek Raven Rock: Hunterdon County, New Jersey Metal 9 Panel Pin-Connected Pratt Through Truss, Fixed 1878 By Builder/Contractor: Lambertville Iron Works of Lambertville, New Jersey
Technical Facts
Main Span Length Structure Length Roadway Width Main Spans NBI Number
127 Feet (38.7 Meters) 129 Feet (39.3 Meters) 15.7 Feet (4.8 Meters) 1 10XX300

Historic Significance Rating (HSR)

Primary Photographer(s): Nathan Holth and Rick McOmber

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

View a historical article discussing the Phoenix Iron and Bridge Works

This extremely rare and beautiful bridge ranks among the most important bridges in New Jersey. It was built by the Lambertville Iron Works of Lambertville, New Jersey which was a company run by William Cowin, who was a fabricator for the three cast iron pony trusses in Hunterdon County such as the one seen on School Street. The bridge is noteworthy as a significant structure built by a local bridge company.

This bridge is a significant example of a bridge using the historically noteworthy and nationally rare Phoenix columns. Phoenix columns are present on the vertical members, top chord, and endpost. It is an extremely early example of a pin-connected Pratt through truss, having been built in the 1870s when the bowstring truss was still a frequently selected form of metal bridge.

This is a very beautiful bridge and it includes a highly decorative builder plaque and decorative cast iron knee bracing at the portals, as well as attractive lattice railings. In addition, the bridge is unusually beautiful because it not only includes decorative finials on the top, at the four corners of the bridge... it actually has one of these decorative finials on top of each panel/connection point. This is unusual, and it adds greatly to the aesthetic qualities of the bridge.

Information and Findings From New Jersey's Historic Bridge Inventory

Discussion of Bridge

Summary: The 1878 iron pin-connected 9-panel Pratt thru truss bridge supported on ashlar abutments is constructed with patented Phoenix columns. It ranks as one of the most important thru truss bridges in the state based on its age, nearly complete state of preservation, and use of Phoenix columns for the compression members. Alterations are minimal and non-intrusive. The bottom lateral bracing joins to a center ring, like the 1870 Clinton bridge (10XXON1), also fabricated by the Lambertville Iron Works.

BIBLIOGRAPHY: Hunterdon County Engineer's Office, Bridge card D300.
Schmidt, Hubert G. Rural Hunterdon: An Agricultural History. New Brunswick: Rutgers University Press, 1945.
Waddell, J.A.L. Bridge Engineering. New York: John Wiley & Sons, Inc., 1925.
Snell, James P., Compiler. History of Hunterdon and Somerset Counties, New Jersey. 1881.
Hunterdon County Freeholders Minutes 1841-1886. Hunterdon County. County Clerk's Office.
Miscellaneous Papers; William Cowin.
U.S. Population Schedules. 1850-1870. Lambertville Beacon. Feb. 28, 1918, p. 1.

PHYSICAL DESCRIPTION: The single span, cast- and wrought-iron, pin-connected Pratt thru-truss bridge is supported on ashlar abutments with flared wingwalls. The trusses consist of inclined portals, top chords, and intermediate verticals, or posts, of patented Phoenix column sections which are joined at each panel point with cast iron pieces that are compression fittings. Inside each piece is a sleeve over which the column section fits. The connecting pins pass through these castings. The bottom chord and principle diagonals are eyebars which are unusual in having a nearly square cross-section as opposed to the more common rectangular cross-section. The counters are rods with loop forged eyes. They also have sleeve nuts for adjustment. The original vertical hangers are eyebars with loop forged eyes. The vertical hanger pin that carries the U-bolt to accept the floor beam also passes through a special casting which supports the bottom chord. The eyebars of the bottom chord continue through this panel point without connecting to the pin, and the two-pronged, bracket-like casting prevents the 2-panel long eyebars from sagging or moving out of position. The top chord lateral bracing system consists of transverse I-section members and X-pattern lateral bracing rods all of which terminate in an upward extension of the top chord node. The bracing connection is topped with an elaborate ball and spire finial. The portal bracing contains decorative cast-iron filigree at the corners. The expansion bearings are probably nested rollers but they are completely obscured by the bearing casting. Some of the steel stringers and corrugated metal deck are modern. Welded steel braces have been added from the portals diagonally to the bottom chord first panel point, as well as welded knee braces between the verticals and top lateral braces. Welded steel gussets are added to the top and bottom pins of the vertical hangers at the first panel points, with two welded bars added to strengthen the hangers. The remainder of the truss is in original condition. The rolled I-beam floor beams have been strengthened with welded top and bottom cover plates.

HISTORICAL AND TECHNOLOGICAL SIGNIFICANCE: The nearly unaltered pin-connected Pratt thru truss bridge is a well preserved example of its type and is technologically distinguished as one of the earliest and most complete bridges built with Phoenix columns in the state. It is also the work of one of the county's foremost second-half of the 19th-century foundries, that of William Cowin. Cowin was the fabricator of the most important 19th century bridges in the region. The Phoenix column, a wrought iron segmental channel riveted together to form a tube of great compressive strength, developed in 1864 by David Reeves of the Phoenix Iron Company at Phoenixville, Pennsylvania. The patented section was used by both the Phoenix Bridge Company and other fabricators in the erection of buildings as well as bridges. By joining the compressive members through compression fittings at cast iron nodes, the Phoenix column "was a great factor causing the substitution of wrought iron for cast iron in compression members of pin-connected bridges," according to noted engineer and author J.A.L. Waddell. The handsome bridge at Raven Rock Road records not only the use of the wrought iron Phoenix column, but also the numerous cast iron elements which serve both utilitarian and decorative purposes. It is an excellent representative of the skill of the 19th-century iron worker The bridge was fabricated by the Lambertville Iron Works, a local foundry which began operation in 1849 as Laver & Cowin, and it continued in operation through most of the second half of the nineteenth century (Schmidt, p. 219). The name was changed to Lambertville Iron Works by 1878, as attested to by the plaque on this bridge, and it was run by William Cowin who is associated with not only this bridge but the three cast and wrought iron spans designed by engineer Francis C. Lowthorp and built in Clinton, Glen Gardner, and Hampton between 1868 and 1870. Cowin's foundry was also making axles, safety boilers, and steam engines (Snell, p. 283). The bridge enjoys integrity of setting and is located in a rural area near two well-preserved early farmsteads on a road joining the nearby villages of Raven Rock and Rosemont. Raven Rock, an area of quarrying industry, was serviced by the New Jersey Railroad, the Delaware & Raritan Canal, and a covered bridge across the Delaware River. In 1880, it boasted a railroad station, a store, a post office and several dwellings. Rosemont was settled in 1754.

Discussion of Surrounding Area

The bridge carries one lane of a lightly traveled paved rural road over an unspoiled stream. Two 18th- or 19th-century farmsteads are nearby. The wooded rural setting includes a nature preserve. The bucolic setting contributes to the overall significance of the span.

Bridge Considered Historic By Survey: Yes

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