UP Boyer River Bridge #1

View an article describing the construction of this bridge

Located along US Highway 30 between Denison and Arion, this large through truss bridge is the eastern of three similar bridges and the first of four bridges carrying a former Chicago & North Western Railway mainline over the Boyer River. Since the railroad first arrived in the area, the Boyer River had been troublesome, often flooding, washing out the tracks and requiring larger bridges to be constructed. The first bridge at this location likely consisted of a timber truss bridge, constructed when the line was first built. In 1874, the bridge was rebuilt with a 119-foot combination Howe through truss span, set onto timber pile substructures and approached by timber pile trestle spans. The bridge was replaced in 1883-84 with a pair of single track 127-foot iron quadrangular lattice through truss spans, set onto stone substructures. Between 1898 and 1902, the C&NW undertook a major reconstruction of this route, double tracking the line between Cedar Rapids, Iowa and Council Bluffs, Iowa. As part of the project, the truss spans were replaced by two double track 86-foot through plate girder spans, set onto stone substructures. It is believed these spans were fabricated by American Bridge Company, and the stone substructures were constructed by the Widell Company of Mankato, Minnesota. After severe flooding in the summer of 1945, it was decided to channelize the Boyer River between Denison and Logan, which also required raising the C&NW line and rebuilding three crossings of the Boyer River. Contracts for the project were awarded in early 1947, with construction beginning that summer and finishing in June 1948. As part of the work, a large through truss span was erected around the 1902-era plate girder spans to minimize impacts to railroad traffic. Currently, the bridge consists of a double track 175-foot, 8-panel, riveted Warren through truss span, approached by a 48-foot steel stringer span on either end. The entire bridge is set onto concrete pile substructures, which are capped with concrete bridge seats.

The truss span follows a standard design for the era, with heavy members, a standard floor and utilitarian portal bracings. The top chord and endposts consist of heavily constructed built-up beams, which are composed of two channels connected by solid plates on the top and X-lacing on the bottom. The bottom chord is constructed using two channels, which are connected by thin transverse plates on both sides. Near the middle of the span, the diagonal members are constructed with a similar design to the bottom chord. Vertical members and the remaining diagonal members are composed using solid beams, typical for spans from this era. The floor system is composed of two plate girder stringers per track and plate girder floorbeams. The portal bracing uses a Warren design, which is formed out of X-laced beams and heavy riveted connections. The sway bracing follows a similar design, and is formed out of L-shaped bars. The upper lateral bracing is constructed using V-laced beams, while the lower lateral bracing is constructed using L-shaped bars. The approach spans each consist of four shallow I-beams, arranged into two sets of two. The substructures are all formed using octagonal piles, which are covered by concrete caps. American Bridge Company fabricated and erected the steel spans, while railroad company forces cast and drove the piles. The Condon-Cunningham Company was contracted to complete the concrete substructures above the concrete piles.

Riveted Warren truss spans became popular for railroad use around the turn of the 20th Century. This design was heavier and more rigid than traditional pin-connected designs, while maintaining simplicity and economy. Between the 1870s and late 1920s, the C&NW had strongly preferred lattice truss designs, using the design nearly exclusively. After the design fell out of favor around 1930, the C&NW switched to using Warren spans, although relatively few Warren spans were ever constructed for the C&NW. Since the initial construction, the bridge has seen no significant alterations. Today, the bridge remains heavily used as part of a Union Pacific Railroad mainline. In addition, portions of the stone abutments from the previous bridge are visible below the truss span. Overall, the bridge appears to be in good condition, with no significant deterioration noted. The author has ranked this bridge as being moderately significant, due to the truss design.