UP IL Route 29 Bridge

View historic articles discussing the construction of this line (digitalized by Internet Archive)

Located south of Pekin, this large through truss bridge carries the former Chicago & North Western Railway over Illinois Route 29. Little is known about the history of this bridge. The first structure at this location consisted of a 72-foot and a 44-foot through plate girder span, set onto a steel bent center pier and timber pile end piers and approached by timber pile trestle spans. The girder spans were fabricated by the King Bridge Company, which had the contract for fabricating all steel bridges along this line. In 1918, the trestle approaches were filled, and new concrete abutments constructed by an unknown contractor. The bridge remained in this configuration until approximately 1940, when it was replaced by the current bridge. Currently, the bridge consists of a 170-foot, riveted quadrangular lattice through truss span, which reuses portions of the old concrete abutments. This span appears to have originally been fabricated in approximately 1905 at an unknown location, and may have been heavily modified upon relocation here. No plaques are present on the bridge, and the superstructure fabricator is currently unknown. The truss uses a typical design for C&NW bridges, including a combination of solid and built-up members, a heavily constructed floor built-up upper and lower chords. By the 1930s, the C&NW had transitioned away from using this type of bridge, clearly indicating the secondhand nature of the bridge.

Because of the nature of the structure and the age of any alterations, it is difficult to tell exactly what modifications have been made to the bridge. An additional panel has been added to each end of the bridge, giving what appears to have been a skewed truss span a square end. This additional panel uses an A-frame portal bracing, with one endpost set vertically. The additional material appears to have been constructed new, and consists of solid beams. It also appears some portions of the upper lateral bracing and sway bracing have been modified, particularly at the ends of the truss. While there is no evidence of alterations to the floor, the floor beams and stringers appear to be a different grade of steel than the remaining superstructure. A number of theories about the history of this structure are plausible. One theory is the truss was reused from a skew span, and the only major alterations made were the addition of the new end panels. It also is possible that this span was narrowed from a double track structure. Railroads often reused steel spans, as this provided a cost effective way to replace older bridges without requiring large amounts of new material. As this structure was likely constructed in the World War II-era, reusing steel would have been critical for rebuilding this bridge. The C&NW extensively reused spans between the late 19th Century and the late 20th Century.

Although the lattice truss design was popular in Europe, few American railroads utilized the design. While Union Pacific Railroad, the Chicago, Rock Island & Pacific Railway and a handful of eastern railroads utilized the design to various extents, no railroad constructed as many lattice truss bridges as the C&NW. Between 1878 and 1930, through trusses constructed by the C&NW nearly exclusively used this design. Although lattice trusses were not popular with American railroads after the 1880s, the C&NW relied heavily on this design, as it had proven to be resilient towards derailments and damage. The main drawback of the design was the unpredictable nature, as the structure was not statically determinant. This span uses a design which includes heavier members than 19th Century versions of this design. However, the design changed relatively little between approximately 1905 and the 1920s. Overall, the bridge appears to be in fair to poor condition, with significant section loss noted throughout the truss span. The author has ranked this bridge as being regionally significant, due to the unusual design.