UP South Skunk River Bridge (Ames)

Located on the east side of Ames, this large deck plate girder bridge carries a former Chicago & North Western Railway mainline over the South Skunk River. The first bridge at this location was a timber pile trestle bridge, constructed when the line was first built. As traffic over this line grew in the 1870s and 1880s, the C&NW made several improvements to timber bridges, replacing them with iron and stone structures. In 1877, the bridge was reportedly rebuilt with three iron 64-foot double intersection Warren pony truss spans. Between 1898 and 1902, the C&NW undertook a large double tracking project between Cedar Rapids, Iowa and Council Bluffs, Iowa. In 1900, a new three span deck plate girder bridge was constructed at this location. It is likely that the pony truss spans were reused elsewhere, either as railroad bridges or as wagon overpasses. In 1949, the bridge was significantly altered, when the east two spans were replaced with a larger deck plate girder span, two steel stringer spans and concrete pile substructures. It is believed that the bridge was reconfigured due to a failing east pier or to widen the clear span. It is unknown if the original east and center spans were salvaged for reuse elsewhere. Currently, the bridge consists of a 110-foot deck plate girder main span and a 75-foot deck plate girder west span, with a 20-foot east steel stringer jump span and an 18-foot west steel stringer jump span. The abutments and west pier consist of stone masonry, while the east and center piers consist of concrete pile piers.

The main and west span superstructures follow a standard design, with two heavy plate girders and an open deck. The jump spans both consist of six shallow beams per track, arranged into two sets of three. Both jump spans are set onto steel blocking. It is unclear if these spans are original to this location, or if they were salvaged from another bridge. The west pier follows a standard diamond shaped design, while the center and east piers use standard octagonal concrete piles with a concrete cap. The abutments also use a standard design, with stepped wing walls extending diagonally from the bridge. Stone for the abutments and west piers consists of a yellow limestone, likely quarried at Mankato, Minnesota. American Bridge Company fabricated the main span, while Wisconsin Bridge & Iron Company fabricated the west span. An unknown contractor fabricated the jump spans, and it is unclear if the concrete pile piers were constructed by railroad company forces or by an unknown contractor. The Widell Company is believed to have constructed the west pier and abutments as part of a larger contract for double track structures along this line. Between the late 1890s and approximately 1903, this company is reported to have constructed much of the stone bridges and culverts along the Iowa Division. Deck plate girder spans were popular for railroad use, as they were durable and easy to construct. The only major alteration to the bridge appears to be the partial encasement of the west abutment, completed in 1951. Overall, the bridge appears to be in fair to good condition, with no significant deterioration noted. The author has ranked this bridge as being locally significant, due to the common design.