Princeton Railroad Bridge

Located in Princeton, this unique pony truss swing span carries the former Chicago & North Western Railway over the Fox River near River Road (County Road D). In the 19th Century, the Fox River was an important navigable waterway in central Wisconsin, connecting Lake Michigan with the Mississippi River via the Wisconsin River. When the Princeton & North Western Railway extended their line north of Princeton, a new swing bridge was required to cross the Fox River on the north side of Princeton. Initially, the bridge consisted of a steel swing span, approached by timber pile trestle spans on the south end. Often, bridges on new lines used timber approaches, as this allowed approach embankments to settle without damaging permanent stone, concrete or steel construction. In 1908-1909, the original south approach was filled, and a new steel stringer span installed on a concrete south pier and abutment, giving the bridge its current configuration. Currently, the bridge consists of a 160-foot, 13-panel, riveted polygonal Warren pony truss swing span, approached by a 25-foot steel stringer span on the south end. The north abutment and north (swing) pier are constructed of stone, while the south pier and south abutment are constructed of concrete. An unknown contractor fabricated the swing span, while the American Bridge Company fabricated the approach span. An unknown contractor constructed the stone substructures, and an additional unknown contractor constructed the concrete substructures. Stone for the northern substructures appears to have been quarried at Duck Creek, Wisconsin; and is the typical white limestone quarried at this location.

Because the Fox River was a smaller navigable waterway, large through truss swing spans were not required. In response, the C&NW designed a unique pony truss swing span to bridge the river at this location, Kaukauna and Green Bay. The swing span uses a rim-bearing design, where the superstructure is set onto a square metal drum, which rotates around a nest of rollers. A locking wheel is located near the center of the span, which has been engaged to prevent the span from turning. At the ends of the span, a transverse cylinder turns a square pin, which unlocks the bridge, raises it and allows it to turn. This primitive design uses an additional bearing block with a slot to lock the bridge in place at the ends. The outer bearing blocks consist of standard rollers, which allow the bridge to turn. This design consists of heavily constructed members and a traditionally composed floor. The endposts, top chord and bottom chord all use heavily built-up members, consisting of channels connected by extensive X-lacing. With the exception of the center panel, the entire top chord is angled. In addition, the endposts used a laced design, a somewhat uncommon feature of this bridge. Most of the diagonal members are constructed of rolled beams, and all vertical members use a solid rolled beam design. The center of the span uses heavily V-laced beams, with a horizontal top chord. The floorbeams and stringer use a plate girder design, and the bridge uses two stringers for the entire length. The south approach span uses a standard design for the era, with six beams arranged into two sets of three. While the abutments and south pier use a standard design, the center pier uses an octagonal shape, typical for swing spans over this waterway. It is believed that the bridge was turned by a T-shaped key, inserted over a square nut which turned the span.

In the early 20th Century, the Fox Waterway lost importance, and navigation ceased at this location. Since then, the bridge has been locked in place. Despite this, much of the original machinery remains in place on the bridge. Polygonal truss spans first became popular in the late 19th Century, as they allowed longer spans while minimizing the amount of material required. Warren trusses also became popular in the early 20th Century, as the riveted connections and heavy members maximized strength while focusing on economy. This particular design was a heavily designed version of an early Warren truss, and only a few examples were ever constructed. The heavily constructed members are unusual for a truss span of this age and length. While built-up beams and rolled beams were common at the turn of the 20th Century, the size and number of rolled members is unusual. The Kaukauna bridge, constructed the same year, was constructed by King Bridge Company. It is possible that this company also constructed this bridge, as they fabricated other bridges along the Princeton & North Western line. After the bridge was abandoned, it was spared demolition when the City of Princeton purchased the structure. A wooden deck and handrails were added to the bridge, and it currently carries a multi-use trail. Overall, the bridge appears to be in fair to good condition, with no significant deterioration noted. The author has ranked this span as being regionally significant, due to the unusual design.