Upper Burger Swing Bridge

Located in Manitowoc, this through truss swing bridge carries the former Chicago & North Western Railway mainline over the Manitowoc River. The first bridge at this location was likely a timber through truss swing bridge, constructed when the line was first built. It is believed this span was likely upgraded during the 1880s with another span of a similar design. In 1899, the bridge was reconstructed, reusing an iron span relocated from Milwaukee, Wisconsin set onto new stone substructures. This span consisted of a riveted quadrangular lattice through truss span, likely fabricated in the early 1880s. It is believed the span was reused from one of the Kinnickinnic River bridges on the south side of Milwaukee, which were both reconstructed in 1898. However, it is unclear which of the spans was reused here. Within 10 years, the lattice span was no longer suitable for mainline traffic this location, and in 1910, the bridge was replaced with the present swing span. It is unclear if the previous bridge was reused elsewhere or was ultimately scrapped. Currently, the bridge consists of a 179-foot, 8-panel, riveted Warren through truss rim-bearing swing span, which reused the stone pier and abutments from the 1899 bridge. Upon construction of the present bridge, the stone pier was repaired by replacing the top row of stone with new concrete. The swing span is comprised of two identical 4-panel halves, joined over the center swing pier by a triangular tower. A rim-bearing swing span works by placing the superstructure onto a metal drum, which rotates on a wheeled track and is turned by a gear system. This span reportedly is hand-turned by inserting a large T-shaped key onto an operating nut.

The superstructure is traditionally composed for the era, with laced endposts, modest sized members and a traditionally composed floor. The top chord, bottom chord and endposts of the superstructure are comprised of built-up beams, consisting of X-lacing on both sides. The diagonal members are mainly composed of X-laced built-up beams, and the vertical members are composed of lighter V-laced beams. Typical of swing spans from this era, the center tower uses a triangular shape, with two X-laced beams on either side of the track, connected by longitudinal beams partway up. In addition, the sides of the tower are connected by a large lattice panel and triangular plates, and the top is connected by a pin and an X-laced beam. The tower is connected to each half by an eyebar, which is pinned at either end. In addition, the tower is also connected by an X-shaped lateral bracing, which are constructed of V-laced beams. The floor system is traditionally composed, with plate girder floorbeams and two stringers. The floorbeams are connected to the bottom chord by large trapezoidal plates, typical of spans from this era. The portal bracing is constructed of an M-frame bracing, composed of V-laced beams. Unique to this bridge, the sway bracing is constructed of beams which are V-laced on all four sides. Similar to other trusses, the upper lateral bracing is comprised of V-laced beams. Also like other C&NW designed swing spans, the metal drum uses a rectangular shape instead of a more traditional circular shape. The substructures follow a standard design, with a circular center pier and standard rectangular abutments. Stone for the substructures appears to consist of a white limestone, and was likely quarried at Duck Creek, Wisconsin.

American Bridge Company fabricated the superstructure at their Lassig plant in Chicago, while the Adolph Green Construction Company constructed the stone substructures in 1899. It is unknown if the concrete additions to the substructures were completed by railroad company forces or by an unknown contractor. Warren trusses became popular in the early 20th Century as a stronger alternative to traditional pin-connected Pratt spans. This design provides strength, durability, economy and a simple design. This span is unusual, as the C&NW nearly exclusively used riveted lattice truss spans for truss bridges constructed between the mid-1870s and late 1920s. It is unclear why the C&NW may have used a more traditional design at this location. One theory is that a lattice truss could not reliably be designed for such a short swing span. Since the initial construction, the bridge has seen no significant alterations, and remains in regular use. While it is not believed that the bridge opens for river traffic anymore, it appears that all required machinery and gearing is still intact. In addition, the original roller end bearings also appear to remain intact. Overall, the bridge appears to be in fair to good condition, with no significant deterioration noted. The author has ranked this bridge as being moderately significant, due to the truss design.