This bridge is one of two similar bridges in this county that are otherwise extremely rare and unique to the county. They are among the shortest pony truss spans ever encountered. The other one is the Stone Sign Post Road Bridge.
This bridge is the more altered of the two. Alterations appear to have been done in the name of historic preservation meaning that the original design and appearance of the bridge was respected for the most part. However many rivets were not replaced in-kind and bolts are present instead. Additionally, it is a safe bet that the original floorbeam was not a galvanized piece of H-pile as is the current modern floor beam. The original floorbeam was likely either a built-up or rolled American Standard Beam type i-beam.
Aside from the extremely short length, the other unusual details include the decorative ball finials at the center of the span on the top chord. The rehabilitation plaque on the bridge is shaped simiarly to how the original (missing) plaque would have been shaped. Finally, the other unsusual detail is the lattice railing with ornamental buttons on them. The railings also have ball finials at the ends. The vertical member in the center of the bridge, with an eye connected to a pin at the bottom chord and threaded into the finial at the top chord, is a structurally unusual detail.
The historic bridge inventory comments are confusing because they make it sound like the loop-forged vertical eyebar member and its finial connector at the top are not original. Certainly these elements are original. Loop-forged eyebars were not being made after 1974! And nobody would have bothered with a decorative finial after 1974 either!
Information and Findings From New Jersey's Historic Bridge Inventory
The 2-panel pony truss bridge is a hybrid modified Warren design with predominantly riveted connections. The reinforced floorbeam is suspended from a pin at the lower panel points. A non-functioning vertical rod extends from the pin and is secured to the top chord by a ball finial. The original lattice railings remain. It's similar to nearby 100D390. Despite 1970s minor alterations, the original design is preserved. It is historically significant as the work of a local fabricator and its design.
The bridge carries one lane of a quiet country road over a minor stream in a wooded setting with sparse housing. It is at the crossroads of three lightly traveled country roads. The setting is unspoiled.
The two-panel, pin-connected slightly skewed Warren pony truss bridge has several unusual features. The top chord is a riveted box member consisting of angles and plate and a continuous cover plate, bent at the inclined end posts. Gusset plates secure the diagonals at the lower panel points. The bottom chord and diagonals are toe-in angles. The vertical member, a modification to the original design made after 1974, consists of two angles with a center separating batten and a central rod which threads through the top chord into a fastening finial. The bottom of the rod is a forged loop that passes around the pin that U hanger for the single flame-cut floor beam. The bridge is supported on random fieldstone abutments with wingwalls. The original medallion and lattice railing remains, but collision damage has buckled the east end post and railing. Concrete scour protection has been added, and a concrete toe wall has been added to the east abutment. Other minor repairs include welded reinforcing plates at the bottom of one inclined end post.
Historical and Technological Significance
The diminutive pony truss bridge is technologically distinguished because it is a hybrid design variation on a Warren truss that reflects the experimental nature of metal truss bridge design in the 19th century. One of two nearly identical spans built over Plum Brook between 1900 and 1903, the designer is not documented, but it is probable that it was the builder of both spans, J. W. Scott, a fabricator from Flemington. According to Hubert Schmidt, Scott operated a foundry which specialized in the manufacture of iron bridges "during the latter part of the nineteenth century." (Schmidt, 220.) Scott also built two thru-truss bridges at Woodfern in Somerset County (18B0511, 18B0512). Like its companion (100D390), the bridge has minor alterations and repairs, but its design integrity and setting have not been compromised. The two bridges are the only documented examples of their design in the state, and while not representing the state of engineering or understanding of sound engineering principles of their day, do represent the variety and idiosyncrasy of bridge designs that characterize the heyday of the metal truss bridge era. Because both bridges are relatively well preserved, both have been evaluated as significant.
Boundary Description and Justification
The bridge is evaluated as individually significant. The boundary is thus limited to the bridge itself and includes the superstructure and substructure.
Hunterdon County Engineer's Office, Bridge card D388. Schmidt, Hubert G. Rural Hunterdon: An Agricultural History. New Brunswick: Rutgers University Press, 1945.
Bridge Considered Historic By Survey: Yes
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