UP Des Moines River Bridge (Des Moines)

Located near Hartford Avenue on the southeast side of Des Moines, this through truss bridge carries a former Chicago, Rock Island & Pacific Railroad (Rock Island) mainline over the Des Moines River. Originally, the "Winterset Branch" reached Des Moines by following present-day Hartford Avenue and Columbus Avenue to 7th Street, where it crossed the Raccoon River on a truss bridge shared by roadway and railroad traffic. By the early 1880s, this arrangement was no longer acceptable to either party, and the Winterset Branch would be realigned. In 1882-1883, a new bridge was constructed at the present location. This bridge consisted of four 153-foot combination Howe through truss spans, set onto stone piers and abutments. It is likely that the bridge was renewed with four iron truss spans in the late 1880s or early 1890s. By the end of the 1910s, the bridge had become too light for traffic, and it was decided to replace it with heavier steel trusses. In late 1919, construction began on replacing the southern three spans with new truss spans, and replacing the northern truss span with timber pile trestle. In the early 1970s, the north approach was filled with embankment and a new overflow bridge was constructed further north, giving the bridge its present configuration.

Currently, the bridge consists of three 153-foot, 6-panel, riveted subdivided Warren through truss spans, set onto stone abutments and piers. The north abutment was rebuilt with a concrete backwall when the north approach was filled. The truss spans follow a standard Rock Island design for the era, with heavy built-up members, a standard floor and heavily constructed portal bracing. Both the top chord and endposts use a heavily built-up design, and are composed of two U-shaped channels joined by a solid plate on the exterior and X-lacing on the interior. The bottom chord is similarly composed, but uses X-lacing on both sides. All vertical members are composed of solid beams, while all diagonal members are composed of heavy X-laced beams. The floor is composed of plate girder floorbeams and plate girder stringers, and the lower lateral bracing is composed of standard steel bars. The portal bracing uses a standard Rock Island design, with two bays of subdivided "X" shapes and diagonal beams forming the heel bracing. All portions of the portal bracing are formed from heavy X-laced beams. The sway bracing uses a standard double intersection lattice design, which is formed from L-shaped bars. The upper lateral bracing is formed from V-laced beams. Both piers and the main portion of the north abutment use a standard diamond shaped design, while the south abutment uses a standard U-shaped design. The north abutment has been retrofitted with a sloped concrete backwall, and the remaining piers and south abutment were repaired with concrete when the bridge was constructed. Stone for the substructures consists of a tan limestone, possibly quarried near Earlham, Iowa.

American Bridge Company fabricated the superstructure, while the substructure was constructed by an unknown contractor. It is unclear if the concrete alterations to the substructure were completed by railroad company forces or by an unknown contractor. Subdivided Warren trusses became popular with some railroads in the 1910s and early 1920s. These spans allowed for greater strength than traditional Warren spans, while still maintaining a relatively simple design. The design is similar to a Baltimore truss span, although it maintains a Warren base configuration. Many similar bridges were constructed for the Rock Island system, and several spans remain intact today. Since the initial construction, the bridge has seen a number of alterations. Both piers and the north abutment have been reinforced with sheet piling and concrete at the base. In addition, the trusses have been strengthened with high strength bolts at some connections. Today, the bridge remains in regular use as part of a Union Pacific Railroad mainline. Overall, the bridge appears to be in fair to good condition, and appears to be well maintained. The author has ranked this bridge as being moderately significant, due to the truss design.