CN Boyer River Bridge #7

Located alongside US Route 30 and the former Chicago & North Western Railway bridge, this through plate girder bridge is the seventh bridge carrying a former Illinois Central Railroad mainline over the Boyer River. When the railroad originally was constructed, the first bridge at this location consisted of a 91-foot and two 45-foot through plate girder spans, set onto concrete substructures. The Boyer River had long experienced severe floods, and by the early 20th Century it was decided to channelize the river. Originally, the river was channelized in the 1920s and 1930s. Railroad records indicate the southern 45-foot span was installed in 1919, using a span fabricated in 1899 at an unknown location. By the 1940s, it was decided that several bridges across the river needed to be lengthened or shifted to allow for a wider channel. In 1946, the bridge was significantly reconstructed, replacing the northern 45-foot span with a 75-foot span, constructing concrete piers and installing timber pile trestle spans at each end of the bridge. This 75-foot span was also fabricated in 1899, and reused from an additional unknown location. It is believed that both the 45-foot and 75-foot spans were reused from somewhere along the Fort Dodge to Omaha mainline, which saw significant improvements during the 1910s and again in the 1940s.

Currently, the bridge consists of a 75-foot through plate girder span on the north end, a 91-foot span in the center and an 87-foot span on the south end. Only the center span is original to this bridge, while the approach spans were reused from other locations. The main spans are set onto concrete substructures, while the approaches are set onto timber pile substructures. The three main spans all use a similar design, with two girders, square girder ends and a standard floor system. Due to the different span lengths, the girders are all different heights. The piers use a standard IC design for the era, consisting of two concrete columns, connected by an arched concrete beam at the top. It is believed this style of pier was used to reduce material and improve channel flow. The approaches also use a standard IC design, consisting of ballast deck spans set onto bents. American Bridge Works fabricated the center span, while the outer spans were fabricated by an unknown contractor. Since American Bridge Works had the contract for all steel bridges on this line, it is likely that these spans were constructed by that firm. It is unclear if the concrete substructures were constructed by an unknown contractor or railroad company forces. The timber components of the bridge were constructed by railroad company forces. Through plate girder spans were popular for railroad use, as they were durable and easy to construct. Since the 1946 reconstruction, the bridge has seen no significant alterations, and remains in regular use. Overall, the bridge appears to be in fair to good condition, with no significant deterioration noted. The author has ranked the bridge as being locally significant, due to the common design.