UP Watertown Plank Road Bridge

View an article discussing construction of the Milwaukee, Sparta & North Western Railway (digitalized by Google)

Located in Wauwautosa, this large through truss and deck girder bridge carries the former Chicago & North Western Railway mainline over the Canadian Pacific Kansas City Watertown Subdivision (former Chicago, Milwaukee, St. Paul & Pacific Railroad), Watertown Plank Road and Underwood Creek. In 1910, subsidiary Milwaukee, Sparta & North Western Railway constructed a new belt line around Milwaukee, with the intention of improving operations for the C&NW. As part of the work, several large bridges were required to cross a number of different railroad lines, roadways and waterways. The largest structure required would cross the Chicago, Milwaukee & St. Paul Railway (Milwaukee Road) Prairie du Chien Division, Watertown Plank Road and Underwood Creek. Work on the new double track bridge began in 1910, and was substantially completed by the end of that year. Currently, the bridge consists of a large 182-foot, 7-panel, riveted Parker through truss span, approached by a 60-foot deck plate girder span on the north end and alternating 60-foot and 30-foot deck plate girder spans on the south end. The bridge is set onto concrete substructures, with the south approach supported by steel towers. In addition, the bridge is set at a slight curve and uses an open deck design.

Typical of truss bridges constructed during this era, the main span is heavily constructed, with large built-up members and heavy riveted connections. Both the top chord and endposts of the truss span are constructed of built-up beams, with V-lacing on the bottom and solid plates on the outside. The bottom chord is similarly composed, with V-lacing on both the top and bottom. All vertical and diagonal members of the truss span are constructed of heavily built-up beams, with V-lacing on both sides. The floor system is composed of plate girder floorbeams and stringers, typical for truss bridges. The truss span uses a standard portal bracing design for the era, with a heavy M-frame design constructed out of V-laced beams. The sway bracing is uses a modified W-shape, and is also constructed out of V-laced beams. Unlike the portal bracing, the sway bracing uses two struts, with the top strut composed of a built-up square with V-lacing on all four sides and the bottom strut using a standard V-laced beam. The upper lateral bracing is also composed of V-laced beams, while the lower lateral bracing uses solid steel bars. Typical of deck plate girder spans from this era, the approach spans are constructed of two heavy plate girders, connected by extensive interior bracing. The abutments use a U-shape design, typical for bridges constructed by the MS&NW, while the piers use a standard square shape. The towers supporting the south approach are composed of two bents. These bents are constructed of two V-laced beams, connected by a transverse plate girder at the top and an X-shaped bracing built of V-laced beams. The two bents are connected by a lateral bracing constructed of V-laced beams.

Pennsylvania Steel Company fabricated all superstructure components, while the Cleary-White Construction Company constructed the concrete substructures. The C&NW often used quadrangular lattice through truss spans, and it is unusual that such a design was not used at this location. Other truss spans constructed as part of this project used a lattice design, such as the nearby Zoo Interchange Truss Bridge. It is possible that the slight curvature of the bridge required a more traditional design. Parker trusses became popular in the 1890s as an alternative to pin-connected Pratt trusses. This design kept the simplicity and strength of the Pratt design, but used a polygonal top chord to allow for longer span lengths. As truss spans with riveted connections became standard around the turn of the 20th Century, Parker spans were most often built with riveted connections. The C&NW seldomly used pin-connected spans, and had mainly relied on riveted lattice trusses for their truss spans since the late 1870s. The use of a Parker through truss at this location is notable, as it is one of very few fixed (non-movable) truss spans constructed for the C&NW between 1880 and 1920 not to use a lattice design. Deck plate girder spans were popular for railroad use, as they were durable and easy to construct. This type of span could be used in conjunction with steel towers to reduce masonry costs. Since the initial construction, the bridge has seen few alterations and both tracks remain in regular use use. Overall, the bridge appears to be in fair to good condition, with minor deterioration noted throughout the bridge. The author has ranked this bridge as being moderately significant, due to the truss design.