CPKC E. Fork Des Moines River Bridge

Located on the west side of Algona, this pony truss bridge carries a former Chicago, Milwaukee, St. Paul & Pacific Railroad (Milwaukee Road) line over the East Fork Des Moines River. The previous bridge at this location was likely either a timber pile trestle or a wooden truss bridge, which had been periodically renewed since it was first constructed. In the late 1890s and early 1900s, the Milwaukee Road invested significant capital into this line, replacing timber bridges with steel and concrete structures. The present structure was constructed in 1898-99. The most recent alterations to the bridge came in 2013, when the original timber pile trestle approaches were replaced with precast concrete modular girder spans. Currently, the bridge consists of a 128-foot, 6-panel, pin-connected Pratt pony truss span, approached concrete modular girder spans on either end. The truss span is set onto concrete piers, while the approaches are set onto steel pile bents with concrete caps. Lassig Bridge & Iron Works fabricated the truss span, while the concrete piers were constructed by labor employed by the Milwaukee Road Bridge & Building Department, as was typical for concrete bridges constructed by this railroad.

The truss span was constructed using a standard Milwaukee Road design, although the length appears to be a slight deviation from more common sizes. Typical of spans of this design, the endposts and top chord consist of built-up beams, which use a plate on the top side and X-lacing on the back side. The bottom chord is composed of built-up beams with X-lacing on both sides. The vertical members of the truss are composed of solid beams, which are connected to the floorbeams by large triangular plates. The diagonal members consist of eyebars, and the counters are composed of round rods with turnbuckles. The floor is composed of two steel stringers and plate girder floorbeams, and the stringers appear to have been replaced in the 2010s. The substructures also follow a standard design, with rectangular piers founded on timber piles.

The Pratt truss design was arguably the most common truss type used for railroad bridges during the second half of the 19th Century. The design provided an economical, simple and durable design. The Milwaukee Road standardized the Pratt design for pony trusses in the mid-1890s, with the standard design largely developed by Alan Riechmann and Onward Bates. The design was refined over a short period, eventually using a heavy built-up bottom chord by the 20th Century. Many examples of this design are still present on former Milwaukee Road lines. By 1905, the Milwaukee Road had largely switched to using riveted Warren pony truss spans. Through plate girder spans were also popular for railroad use, as they were durable and easy to construct. Since the initial construction, the original stringers and approaches have been replaced. Overall, the bridge appears to be in fair to good condition, with no significant deterioration noted. The author has ranked this bridge as being moderately significant, due to the common design.