CPKC Des Moines River Bridge (Ottumwa)

Located in Ottumwa, this through truss bridge carries a former Chicago, Milwaukee, St. Paul & Pacific Railroad (Milwaukee Road) mainline across the Des Moines River. The first bridge at this location was likely a temporary timber pile trestle, intended for constructing this bridge and the mainline towards Kansas City. In 1887, the bridge was replaced by four 142-foot, 8-panel, pin-connected Pratt through trusses, set onto stone piers. This bridge was fabricated by an unknown firm, and used several features typical of mid-1880s truss spans, including light built-up members, a standard floor and crested lattice portal bracing. By 1909, the original bridge had become too light for traffic. In response, the Milwaukee Road designed a new bridge to replace the 1887-era bridge, reusing the original piers. The design of the new bridge was finalized in November 1909, and construction occurred through the 1910 construction season. After the new bridge was constructed, the four truss spans were reused on two separate bridges in 1911. Two spans were reused at Bridge #M-188 across the Chippewa River in Eau Claire, Wisconsin as part of a larger bridge constructed from secondhand spans. The other two spans were reused at Bridge #H-716; which crossed the Maquoketa River south of DeWitt, Iowa. Bridge #M-188 now serves a popular trail, while Bridge #H-716 was removed in the early 1930s and subsequently scrapped.

Currently, the bridge consists of four 142-foot, 6-panel, riveted Warren through truss spans, set onto concrete encased stone piers. In addition, a short concrete slab span approaches the bridge on the north, although this span forms a portion of the north abutment. On the south end, the bridge was originally approached by timber pile trestle spans, which were replaced by concrete modular girder spans set onto concrete capped steel pile substructures in 2023. The truss spans follow a typical late-1900s era Milwaukee Road truss design, with a combination of built-up and solid members, a standard floor and a utilitarian portal design. Both the top chord and endposts consist of heavily built-up beams, composed of two U-shaped panels connected by a solid plate on the top and heavy X-lacing on the bottom. The bottom chord uses a similar design, consisting of two U-shaped beams with V-laced beams on either side. The vertical members consist of both solid beams and light V-laced beams, used in an alternating pattern with the solid beams at the ends and centers and the V-laced beams at the 2nd and 4th panels. The diagonal members are similarly composed, with solid beams at the outer two panels and V-laced box beams at the center two panels. The floor system is composed of a standard design, with two plate girder stringers and plate girder floorbeams at the panel points. The portal bracing uses a standard A-frame design, which is constructed from L-shaped bars. Similarly, a lattice design is used for the sway bracing, which is also composed of L-shaped bars. The upper lateral bracing is composed of V-laced beams, while the lower lateral bracing is composed of L-shaped beams. The piers were originally constructed using a diamond shape, which was encased in concrete when the present bridge was constructed. The north abutment uses a standard Milwaukee Road design, with sloped wing walls and an extended slab behind the abutment.