BNSF Des Moines River Bridge (Keokuk)

Located along US Route 61 south of Keokuk, this large through truss bridge carries the former Chicago, Burlington & Quincy Railroad over the Des Moines River. The first bridge at this location was likely a timber truss bridge, set onto timber pile piers. In 1883, the bridge was replaced by a new pin-connected Pratt through truss bridge, constructed for both roadway and railroad use. This bridge used lightweight built up members, light chords and a decorative portal. This bridge was set onto stone abutments and stone and steel cylinder piers. By the early 20th Century, the bridge had become too light for traffic. In 1904 and 1910, the bridge was replaced by the current bridge. Upon construction of the current bridge, the old bridge spans are believed to have been reused throughout the CB&Q system. The only significant alteration to the bridge since is the addition of concrete slab approaches on either end.

Currently, the bridge consists of from south to north, one 147-foot, 8-panel, pin-connected Pratt through truss span, one 174-foot, 9-panel span, two 147-foot spans, one 188-foot, 9-panel span and an additional 147-foot span of the same design. A 14-foot concrete slab span approaches the bridge on either end, and all substructures of the bridge are constructed of concrete. It is currently unknown which spans were fabricated in 1904, and which were fabricated in 1910. American Bridge Company fabricated the spans, and the substructures were constructed by railroad company forces. The truss spans run at a 26.5-degree skew, which is necessary to match the current of the river. All trusses contain built-up members, a combination of riveted and pin-connected members and an M-frame portal. The 188-foot span (span #5) contains an A-frame portal and slightly heavier members. The skew of the bridge is accomplished by the use of an additional 9-foot panel on each end of the span, an unusual feature of this bridge. In addition to the skew, the northern end of the bridge is set onto a slight curve. It is believed the present bridge originally carried roadway and railroad traffic, although the roadway deck has long since been removed.

This design of truss is very similar to other CB&Q trusses constructed in the early 20th Century. These spans used heavy members and a combination of riveted and pinned connections. Pratt trusses were commonly used for railroad truss spans in the late 19th Century, as the design was economical and strong. However, this design was mostly superseded by riveted Warren spans in the early 20th Century. The CB&Q continued to use the Pratt design into the 1910s. Overall, the bridge appears to be in fair to good condition, with no significant deterioration noted. A number of locations of the bridge have been strengthened, and it appears some of the spans were painted at different times. The author has ranked this bridge as being regionally significant, due to the size of the bridge.