Kaukauna Swing Bridge

Located in Kaukauna, this unique pony truss swing span carries a former Chicago & North Western Railway industrial lead over the Fox River Navigation Canal between Kaukauna Locks #2 and #3. When first constructed, the Milwaukee, Lake Shore & Western Railroad (MLS&W) and C&NW were located on opposite sides of the Fox River with no connection. In 1881, the MLS&W built a short spur across the Fox River, and in 1888 the C&NW constructed an additional section to connect the two systems. After the MLS&W was acquired by the C&NW, this connection became an important industrial lead in Kaukauna, serving a variety of industries along the Fox River. 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. The first bridge at this location was a wooden through truss swing bridge, constructed when the line was first built. By the early 20th Century, the canal needed to be widened and wooden truss bridges were no longer suitable for most railroad traffic. Work on the present bridge began in 1900, and was completed in 1901. Currently, the bridge consists of a 160-foot, 13-panel, riveted polygonal Warren pony truss swing span, set onto stone substructures. King Bridge Company fabricated the superstructure, while an unknown contractor completed the substructures. Stone for the substructures consists of a white limestone, likely quarried at Duck Creek, Wisconsin.

Because the Fox River was a smaller navigable waterway, large swing spans were not required. In response, the C&NW designed a unique pony truss swing span to cross the navigation channels of the Fox River. Three spans were constructed, including one at this location, one at Princeton and one at Green Bay. This design consists of heavily constructed members and a traditionally composed floor. The endposts and top chord both use a built-up design consisting of two channels with X-lacing on both sides. The bottom chord uses a similar design with V-lacing on both sides and heavier channels. With the exception of the center panel, the entire top chord is sloped. In addition, the endposts used a laced design, a somewhat uncommon feature of this bridge. Most of the diagonal members are constructed of built-up solid 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 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 can be engaged to prevent the span from rotating. 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. The center drum consists of a square shape, and is integral to the span. The span remains operational, and is driven by an electric motor. The abutments use a standard design with stepped wing walls, while the center pier consists of a square shape.

In the early 20th Century, the Fox Waterway lost importance for commercial traffic. In the 1980s, the Army Corps of Engineers recommended that the lock system be dismantled, due to the lack of commercial traffic. In 2004, the ownership of the system was transferred to the State of Wisconsin. In 2017, the canal at this location was restored after years of disuse and is now open to recreational craft during the summer months. As part of the restoration of the canal, the bridge was retrofitted with a new motor and other improvements were made to the operating machinery. 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 built-up solid beams were common at the turn of the 20th Century, the size and number of solid members is unusual. Today, the bridge serves as a spur for the Canadian National Railway, connecting to a paper mill south of the bridge. 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.