Brook Road Bridge

Information and Findings From New Jersey's Historic Bridge Inventory

 Summary

The pin-connected Pratt pony truss bridge supported on concrete abutments has a laminated timber deck. Alterations are limited to the addition of welded outriggers and steel railings were welded to the truss. The span is distinguished because it is a very well-preserved example of an important early metal truss bridge type. Located within undeveloped parkland, the integrity of the original setting has not been compromised. Date of construction and builder are undocumented.

Setting/Context

The bridge carries a 1-lane, 2-way street over a shallow stream in a wooded undeveloped area located within the Flat Brook-Roy Wildlife Management Area.

Physical Description

The single-span pin-connected half-hip Pratt pony truss bridge supported on concrete abutments, spans 46' and carries an 11'6" wide road. The four-panel truss is composed of standard-design members. Upper chords are back-to-back channels with cover plate on the top and lattice on the bottom of the built-up box member. Bottom chords are pairs of rectangular section eye bar at center bays and circular section bars at end bays. Verticals are back-to-back angles joined by lattice. Diagonal members are pairs of square section bars, and counters are single circular section rods. Outriggers were welded to the truss at each panel point at unknown dates, and a steel channel guide rail has been was welded to each inside truss face. The span has a laminated timber deck.

Historical and Technological Significance

The ca. 1890 Pratt pony truss bridge is a very well-preserved example of an increasingly uncommon bridge type (Criterion C). The span, although undocumented to date of construction and builder, is a virtually unaltered example of the most common late-19th century bridge type. It is one of four eligible pony truss spans in Sussex County (1900D07, Smith Mill Road, Frankford Twp.; 1900E10, Scott Road, Franklin Borough; 1900W06, Main Street, Walpack Township). The bridge is located within the undeveloped Flat Brook-Roy Wildlife Management Area, and the integrity of setting has not been compromised. Through the third quarter of the 19th century, a variety of truss designs were developed and patented, but the one that proved to be the most economical, efficient, and easy to fabricate and erect in the field was the Pratt truss, which has the verticals in compression and the diagonals in tension. The truss was patented by Thomas and Caleb Pratt in 1844, and the earliest examples were a combination of wood (for the compression members) and iron (for tensile members). The Pratt truss went on through the century to become the most common design, and it was not until technological advances made it possible to execute reliable field riveted connections after about 1890 that the Warren truss superseded the pin-connected Pratts on the nations highways and byways.

Boundary Description and Justification

The bridge is rated individually eligible. The boundary is limited to the superstructure and substructure of the bridge itself.

Sources

Sussex County Engineer's Office. Bridge Files.

Bridge Considered Historic By Survey: Yes