RCP&E Cheyenne River Bridge (Oral)

Located north of the small town of Oral, this large through truss bridge carries a former Chicago & North Western Railway secondary line across the Cheyenne River. The first bridge at this location was a timber Howe through truss bridge, approached by timber pile trestle spans and set onto timber substructures. By the turn of the 20th Century, wooden truss bridges were no longer suitable for most railroad bridges. The main portion of the bridge was reconstructed with a pair of secondhand through truss spans in 1910, which were set onto concrete piers and approached by timber pile trestle spans. Additional alterations to the bridge were made in 1926, when the northern four deck plate girder spans were installed on new steel cylinder piers. Further alterations were made in approximately 1930, when the southern three deck plate girder spans were installed, and much of the north approach filled. The most recent alterations came in the early 21st Century, when the remaining timber components of the bridge were rebuilt with new stringers, giving the bridge its present configuration. Currently, the bridge consists of a 172-foot, 7-panel, pin-connected Pratt through truss north span (span #9) and a 196-foot, 8-panel span of the same design (span #8). The south approach is composed of a 44-foot deck plate girder span (span #7) and six 38-foot deck plate girder spans (spans #1 through #6). In addition, the north end is approached by four timber pile trestle spans, while the south end is approached by six timber pile trestle spans. The main piers (piers #8, #9 and #10) are constructed of concrete founded on timber piles, while piers #1 through #7 are constructed of steel cylinders filled with concrete.

The truss spans were originally fabricated in 1897-1898 for use at the Mississippi River crossing at Clinton, Iowa. The northern span was originally part of the main channel bridge, while the south span was originally part of the east channel bridge. The truss spans are tall and heavily constructed, with massive members and large pinned connections. Both the top chords and endposts are composed of built-up beams, consisting of two channels connected by a solid plate on the top and X-lacing on the bottom. The bottom chords are unique, and are composed of a built-up beam with X-lacing on both sides at the outermost two panels of each span and eyebars at the center panels. Unique to this bridge, the bottom chord is set on top of the floorbeams, which gives this bridge an unusual appearance. The vertical members and crash bars of both spans are composed of V-laced beams, while the diagonal members are composed of eyebars. The floor system uses a slightly modified version of a standard design, with four heavy plate girder stringers and heavy plate girder floorbeams. The bottom chord and truss members are connected to the floorbeams by use of a hanger system, consisting of two U-shaped brackets. Due to the depth of the truss floor, no lower lateral bracing is used in either span. The upper lateral bracing is composed of square steel bars, which are connected to the top chord and sway bracing by use of a U-shaped clamp, which is pinned through a plate in the top chord. Unique to this bridge, the portal bracing uses a pedimented design, with a deep lattice beam underneath. Rounded heel bracing is present underneath the lattice beam, which has decorative holes cut through it. A date cutout is present on the top beam of the portal bracing, but has been covered up by a steel plate. The sway bracing is composed of a V-laced strut on top and a solid strut below, which are connected by a similar lattice beam to the portal bracing.

The approach spans follow a typical design for shallow plate girders, and use four girder lines. All seven spans are nearly identical in construction, but the northern set of spans use a different color paint from the southern spans. The main piers of the bridge use a typical design for the era, and consist of diamond shaped structures. Risers have been added to the tops of the piers to account for the different heights of the spans and the different thicknesses of the floor systems. The approach piers use a standard steel cylinder design, consisting of oval-shaped structures which are filled with concrete. This style of pier was popular during the early 20th Century, due to its ability to be constructed with minimal interruption to traffic. Detroit Bridge & Iron Works fabricated the truss spans, while American Bridge Company fabricated the approach spans. Cleary-White Construction Company constructed the main piers (piers #8 through #10), while the approach piers (piers #1 through #7) were constructed by unknown contractors. Railroads often reused steel and iron spans, as it was a cost effective way to replace aging bridges on branch lines without requiring large amounts of new material. In particular, heavy truss spans used at major river crossings were popular candidates for reuse. When the Clinton bridge was replaced in 1909, the four 1897-98 spans were salvaged and reused at various locations. Two spans were installed here, while one span was installed at Whitewood, South Dakota; and the fourth was installed at Niagara, Wisconsin. All four spans continue to exist as of 2026.

The C&NW was unique for its choice of truss design, as this railroad preferred to use lattice spans wherever possible. Between the late 1870s and late 1920s, the C&NW nearly exclusively used various types of lattice trusses. This design was preferred by C&NW bridge engineers, as it provided greater strength and resiliency. The use of more traditional truss designs on the C&NW was uncommon during the late 19th and early 20th Century. Only a handful of non-lattice style trusses were known to have been constructed. In particular, the C&NW ordered several heavy Pratt truss spans in 1897-1898 for use at the Clinton bridge and another mainline bridge across the Cedar River. The use of this design likely was due to the Detroit Bridge & Iron Works designing the spans to meet the requirements of the crossing instead of the C&NW advocating for a lattice design. Pratt truss designs were arguably the most popular railroad truss design in the second half of the 19th Century, due to their strength, economy and simple design. By the turn of the 20th Century, this design had largely been superseded by heavier riveted Warren trusses, which provided greater strength and rigidity. Currently, this bridge remains in regular use, and the structure has seen no significant alterations. Overall, the bridge appears to be in fair to good condition, with no significant deterioration noted. The author has ranked this bridge as being regionally significant, due to the truss design and history of the spans.