UP Wapsipinicon River Bridge

Located east of Wheatland, this quadrangular lattice through truss bridge carries a former Chicago & North Western Railway mainline over the Wapsipinicon River. The first bridge at this location was likely a wooden through truss bridge, constructed when the line was first built. It is believed that this bridge was likely replaced by an iron through truss bridge of an unknown design in the 1870s. In 1888, the bridge was reconstructed with a pair of single track 157-foot quadrangular lattice through truss spans, set onto stone substructures. These spans were fabricated by the Lassig Bridge & Iron Works, and featured a flat decorative portal bracing, typical of spans from the mid to late 1880s. In 1891, the bridge was widened for a second track by extending the stone substructures and adding two similar single track spans. These spans were also fabricated by the Lassig Bridge & Iron Works, and featured a standard Lassig-style pedimented portal bracing. As trains became heavier in the early 20th Century, it was decided to upgrade this bridge. In late 1911, crews began working to reconstruct the substructures with concrete. By early 1912, new steel truss spans were installed, and the old bridge was dismantled. It is believed that the four single track spans from the previous bridge were reused at other locations on the C&NW system, although it is not clear where. Currently, the bridge consists of a pair of double track 157-foot quadrangular lattice through truss spans, set onto concrete substructures.

The truss spans use a standard design for double track lattice spans from this era, with heavy members, a standard floor and M-frame portal bracing. The top chord and endposts both consist of built-up beams, composed of two heavy U-shaped channels connected by V-lacing on the interior and a solid plate on the exterior. The bottom chord uses a similar design, with V-lacing and short plates on both sides. The vertical members and outer two compression members consist of solid beams. The remaining compression members consist of two different styles of V-laced beams. All of the tension members consist of L-shaped bars. The floor system uses two plate girder stringers per track, and plate girder floorbeams at the panel points. The lower lateral bracing is composed of L-shaped bars. Typical of spans from this era, the portal bracing uses an M-frame design, composed exclusively of V-laced beams. Both the sway bracing and upper lateral bracing consist of V-laced beams of a similar design. The abutments use a standard rectangular design, with short sloped wing walls. The center pier has been heavily modified with sheet piling and concrete encasement. American Bridge Company fabricated the superstructure, and it is unclear if the substructure was constructed by railroad company forces or by an unknown contractor.

This type of truss design is relatively uncommon throughout the United States. However, a few railroads preferred the design, such as the Chicago, Rock Island & Pacific Railway (Rock Island), the Chicago & North Western Railway (C&NW) and the Chicago, St. Paul, Minneapolis & Omaha Railway (Omaha Road). Spans constructed in the late 1870s and early 1880s for the C&NW featured an arched and pedimented lattice portal bracing, light sway bracing and laced members. The second generation was nearly exclusively constructed by Lassig Bridge & Iron Works between 1884 and 1900, and featured heavier members and a pedimented portal bracing. While the design fell out of favor for the Rock Island and Omaha Road around the turn of the 20th Century, the design remained popular with the C&NW into the 1920s. 19th Century versions of this design were primarily constructed out of iron, while 20th Century versions of this design used much heavier members and were constructed of steel. The C&NW preferred this design, as it was both strong and demonstrated great resilience in case of a derailment. A handful of spans using this design were constructed along this route, primarily to cross large rivers. Since the initial construction, the bridge has seen a handful of few alterations. The center pier was rebuilt with sheet piling and concrete encasement in approximately 1970. In addition, certain rivets throughout the truss were replaced by high strength bolts in the early 21st Century. Today, the bridge remains in regular and heavy use as part of a Union Pacific Railroad mainline. 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.