RI E. Branch West Nishnabotna River Bridge

Located south of Avoca, this through truss bridge carries a former Chicago, Rock Island & Pacific Railway (Rock Island) branch over the East Branch West Nishnabotna River. Little is known about the history of this bridge. The first bridge at this location was likely a timber pile trestle, constructed when the line was first built. It is unclear if the bridge was later rebuilt with a timber truss bridge. In approximately 1910, the bridge was reconstructed with a secondhand iron through truss span, giving the bridge its present configuration. Currently, the bridge consists of a 110-foot, riveted quadrangular lattice through truss span, set onto timber pile piers. The south end is approached by four timber pile trestle spans, while the north end is approached by seven timber pile trestle spans. The truss span was originally fabricated in approximately 1885 for use at an unknown location, before being reused here. It is possible that the truss was reused from Perlee, Iowa; where a 110-foot truss span was erected in 1885 and replaced in the early 20th Century. In Rock Island annual reports, this was the only span of this size noted to have been constructed. An unknown contractor fabricated the truss span, while the timber components were constructed by railroad company forces. While unclear, it is possible that the truss was fabricated by Lassig Bridge & Iron Works, which fabricated many lattice trusses for Midwest railroads.

The truss span follows a standard design for mid-1880s lattice truss spans, with light members, a standard floor and a decorative portal bracing. The top chord and endposts are both constructed out of built-up beams, which use two channels connected by thin plates on the bottom and a solid plate on the top. The bottom chord is constructed using two T-shaped plates, which are connected by short plates throughout. The diagonal members consist of two different designs, with standard L-shaped bars for the tension members and built-up beams consisting of two L-shaped bars connected by V-lacing for the compression members. The floor system consists of plate girder floorbeams, which are set above the bottom chord and deck is carried by light I-beam stringers. The portal bracing uses a typical lattice pedimented design and solid triangular heel bracings with flower-shaped cutouts. Unlike later spans, the portal bracing is constructed using only plates and thin bars. Both the upper and lower lateral bracing are constructed using iron bars. The timber pile piers and approaches follow a standard design, with round piers and standard stringers.

This type of truss design is relatively uncommon throughout the United States. However, a few railroads preferred the design, such as the Chicago, Rock Island & Pacific Railway (Rock Island), the Chicago & North Western Railway (C&NW) and the Chicago, St. Paul, Minneapolis & Omaha Railway (Omaha Road). The Rock Island began using the design in the early 1880s as an alternative to iron pin-connected spans. Spans constructed in the 1880s and 1890s used lightly built-up members and a decorative pedimented portal bracing. At the turn of the 20th Century, the Rock Island constructed a handful of significantly heavier trusses of this design, before switching to more traditional designs. The main detraction of the design was its statically indeterminate nature, while the design performed well in case of a derailment. Railroads often reused steel and iron spans, as it provided a cost effective way to build bridges without requiring large amounts of new material. Since the initial construction, the bridge has seen no significant alterations. After abandonment, the bridge and adjacent right-of-way was reverted to a private owner. Additional planks were added above the ties to allow for farm equipment to pass over the bridge, and the bridge now connects two farm fields. Overall, the bridge appears to be in fair condition, with minor deterioration to the truss or timber components noted. The author has ranked the bridge as being regionally significant, due to the truss design and age.