IAIS Raccoon River Bridge

Located along County Road F90 west of Booneville, this large through truss bridge once carried a former Chicago, Rock Island & Pacific Railroad mainline over the Raccoon River. The first bridge at this location was likely a wooden truss bridge, constructed in 1869 when the line was first built. It is unclear if the first bridge was upgraded later in the 19th Century, although one article suggests the bridge remained a wooden structure in 1900. Starting in 1900, the Rock Island began a major improvement program, replacing the timber bridges along this line with concrete and steel structures. That summer, the original bridge was replaced with four through truss spans, set onto new concrete substructures. Significant repairs were made to the bridge in 1942, when the center and west piers were reconstructed with new concrete piers. In the late 1980s or early 1990s, the west end of the bridge was reconstructed due to a failing abutment. As part of the work, a new steel pile skeleton was constructed around the original west abutment, and two timber pile trestle spans were added to the west end. In 2014, the west approach was reconstructed with two steel stringer spans, set onto a new steel pile pier and abutment, giving the bridge its final configuration.

At the time of replacement, the bridge consisted of four 147-foot, riveted quadrangular lattice through truss spans, approached by a 10-foot and a 20-foot steel stringer span on the west end. The east abutment and eastern three piers were constructed of concrete, while the west abutment, west approach pier and west pier were constructed of steel piles. The truss spans followed a standard design for lattice trusses constructed by the Rock Island at the turn of the 20th Century, with heavily built-up members, riveted connections and a lattice portal bracing. Both the top chord and endposts were constructed using built-up beams, composed of two U-shaped channels with a solid plate on the top/exterior and V-lacing on the bottom/interior. The bottom chord was constructed of two parallel U-shaped channels, connected by thin plates throughout the chord. At the hips, a vertical member consisting of four L-shaped bars connected by thin plates connected the top chord, endpost and bottom chord. The diagonal members consisted of three different designs, with solid beams at the end three compression members, V-laced beams at the center compression and tension members and light beams composed of two L-shaped bars at the outer tension members. Midway up the truss web, the vertical member and outer compression member were connected by a large trapezoidal plate, and connected to the endposts by two L-shaped bars. Crash bars were also present between the bottom chord and endpost, and consisted of two sets of two L-shaped bars, connected by a wide V-lacing and thin plates. The portal bracing used a double intersection lattice design, with four sets of "X"s. Heel bracing was constructed with a triangular shaped plate, with a triangular cutout. The sway bracing consisted of lightly constructed V-laced beams. The floor followed a standard design, with plate girder floorbeams at the panel points and two plate girder stringers. Both the upper lateral bracing and lower lateral bracing were constructed of square bars.

The substructures used multiple different designs, due to the different construction dates. The east abutment was composed of a simple rectangular abutments, without wing walls. The east pier (pier #1) was similar, consisting of a rectangular shape. Pier #2 was composed of an oval shape, with scrap rails set into the noses to form an icebreaker. Pier #3 appears to have been heavily modified at different dates, and consisted of a rectangular structure reinforced with concrete, steel H-piling and sheet piling. The west pier (pier #4) was composed of steel pile bents, placed on either end of the original west abutment. These bents were connected by two sets of two steel girders, and the bearing blocks of the west truss span were placed on these girders. Based on cut marks, it appears that the steel girders were salvaged from another location and reused here. The west approach substructures consisted of a standard modern concrete capped steel pile bent and abutment. Lassig Bridge & Iron Works fabricated the truss spans, while railroad company forces constructed the east abutment and east pier (pier #1). In April 1900, an article stated that the Rock Island would likely award contracts to multiple firms for fabricating steel bridges required for 1900. A May 1900 article indicates that the entire years work was awarded to Lassig Bridge & Iron Works, with all masonry work being constructed by railroad company forces. Lassig Bridge & Iron Works became part of American Bridge Company later that year, although it is believed that Lassig finished this bridge prior to being consolidated into American Bridge Company. It is unclear if piers #2 and #3 were constructed by railroad company forces or by an unknown contractor, and builders of the west pier (pier #4) and west approach are also unknown.

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, with a functional portal bracing and more solid members. It is believed the last spans of this design were fabricated for the Rock Island in approximately 1901 or 1902, when the railroad switched to using a more traditional riveted Warren design. The main detraction of the design was its statically indeterminate nature, while the design performed well in case of a derailment. In 2019, a project was begun to replace the bridge with a modern steel stringer bridge, constructed immediately south of the structure. The new bridge was opened to traffic in mid-2020, and the old bridge demolished soon after. At the time of replacement, the bridge was in fair to poor condition, with several areas of deterioration and temporary repairs made. The author has ranked this bridge as being regionally significant, as it was a large scale example of a late generation lattice truss constructed for the Rock Island.