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Rockafellows Mill 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
Rockafellows Mill Bridge
Rockafellow Mill Road Over South Branch Raritan River (Red Rock Lake) Rockafellows Mill: Hunterdon County, New Jersey Metal 6 Panel Pin-Connected Pratt Through Truss, Fixed 1900 By Builder/Contractor: Wrought Iron Bridge Company of Canton, Ohio
Technical Facts
Rehabilitation Date Main Span Length Structure Length Roadway Width Main Spans NBI Number
2010 138 Feet (42.1 Meters) 140 Feet (42.7 Meters) 15.4 Feet (4.7 Meters) 1 10RQ164

Historic Significance Rating (HSR)

Primary Photographer(s): Nathan Holth and Rick McOmber

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

This bridge was built in 1900 by the Wrought Iron Bridge Company. Since the company was absorbed into the American Bridge Company in that same year, this bridge would have been among the last bridges built by the Wrought Iron Bridge Company. The bridge contains six panels. The portal bracing is an a-frame design. This bridge is an attractive, traditional example of its type and is a contributing resource for a historic district.

When documented by HistoricBridges.org in 2008, this bridge retained original lattice railing, but no plaque was present. There were welded alterations at several connections on the bridge. The bridge also displayed no finials and portal cresting. In 2010, the bridge was rehabilitated in a historically sensitive manner. Also, a standard design Wrought Iron Bridge Company plaque reappeared on the portal bracing. Additionally, portal cresting and finials were present atop the portal bracing. It is unclear whether these elements are original materials from this bridge that had been in storage, or if they are replicas of original materials that are either in storage or documented in photos and/or drawings, or whether they are original creations developed based on details found on other similar bridges. One thing is certain, which is the date marker on two of the finials is a modern creation since it lists 2010, the rehabilitation date. In any case, these elements greatly enhance the beauty of this historic bridge.

As mentioned, this was a historically sensitive rehabilitation, however, a couple alterations need to be noted. The floor beams were replaced. A far greater concern, the original lattice railing panels were also removed. A crash-resistant guardrail system was installed with a modern lattice railing meant to simulate a historic lattice railing integrated into this guardrail system. This modern lattice does not match the lattice pattern of the original railing. It is unclear why the original lattice railing panels could not have simply been used rather than fabricating the modern lattice panels. The lattice is not the crash-resistant part of the guardrail system, which is the two-tube system present in front of the lattice. With historic pony and through truss bridges, HistoricBridges.org strongly supports and advocates for the installation of a crash-resistant guardrail system that protects the trusses from impact damage by cars. However, this support also comes with a strong urging that the original railing be left in place on the bridge for the beauty of the bridge and the historic integrity of the bridge as well. It should however be noted that both the modern lattice and the crash-resistant guardrail are painted brown, while the truss is painted green. This helps visitors interpret and understand the historic bridge, since when crossing the bridge, everything visible that is painted brown is not original to the bridge.

The rehabilitation work of the bridge itself deserves brief discussion. The bridge had a posted three ton weight limit prior to rehabilitation and following rehabilitation the bridge's condition was improved allowing for a higher posted weight limit of 15 tons. The bridge was dismantled with its parts being cleaned, restored, and repainted in a shop setting. This method of rehabilitation for pin-connected truss bridges is the best method because it fully eliminates all pack rust and allows the fabricator to address all areas of section loss and pack rust in the bridge members. What is unusual is the method in which the bridge was dismantled and reassembled. A temporary Bailey truss was installed inside the truss to hold the bridge together while it was being dismantled and also during reassembly. This method varies from the typical method of simply moving the entire bridge off and on its abutments by picking the truss with a crane, with dismantling and reassembling taking place on nearby land. The Bailey truss method employed here is continuing evidence that numerous methods are available to restore historic metal truss bridges, even bridges where traditional methods are not feasible. The Bailey truss method is useful for situations where nearby land for disassembly and reassembly on land is not available, or in situations where space limitations make the use of a large crane to lift the entire truss difficult.

Information and Findings From New Jersey's Historic Bridge Inventory

Discussion of Bridge

The bridge is a six panel riveted pin-connected Pratt thru truss bridge. It is supported on rebuilt concrete abutments and stone wing walls. Modifications include welded repairs to bottom chord and verticals and welded gusset panels. Some pins are bent, and the eyebar bottom chord is twisted. Double pins are used for the lower chord at end panel points only. It has original lattice railing. The well-preserved bridge is rated as contributing element in the National Register district nomination.

Discussion of Surrounding Area

The one-lane bridge carries an unpaved, 2-lane rural road over the South Branch of the Raritan River. It is located in a wooded rural setting but the urban environment is encroaching. The mill for which the dirt road is named does not appear to have survived, but remains of the dam are visible.

Bridge Considered Historic By Survey: Yes

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Photos and Videos: Rockafellows Mill Bridge

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