DME Iowa River Bridge (Tyson Spur)

Located along Iowa Highway 70 north of Columbus Junction, this Parker through truss bridge once carried a Chicago, Rock Island & Pacific Railroad (Rock Island) mainline over the Iowa River. When the BCR&M was first constructing between Burlington and northern Iowa, three significant bridges were required. Two bridges across the Cedar River were required near Cedar Rapids, and a third large bridge was required across the Iowa River north of Columbus Junction. Contracts for the Iowa River bridge were awarded in February 1870, and work began soon after. The first bridge at this location consisted of two 154-foot and one 153-foot pin-connected combination through truss spans, set onto stone piers and approached by timber pile trestle spans. The substructure seems to have been part of the main contract for the First Division, which was likely a pool of smaller individual contractors. The superstructure was constructed by Boyington & Rust of Chicago, Illinois and shipped to the site on railroad cars. The bridge was reportedly completed in early June 1870, which allowed construction on the new railroad to progress north. This bridge was one of the final bridges constructed by this firm before it was reorganized into the American Bridge Company (of Chicago) in August 1870. Combination trusses included a wooden frame with iron tension members, and were viewed as superior to all-wood trusses. Photos of the combination trusses seem to show some unusual variation of a Pratt and Warren design, with an iron bottom chord, wooden endposts and top chords and V-laced iron compression members at the center of the structure. An additional wooden tension member, approximately the size of the endpost, appeared at the second and second to last panels. Without additional photos, it is impossible to tell what truss pattern this may have been.

Starting in the mid-1880s and continuing into the 20th Century, the BCR&N invested significant capital into this line, replacing aging bridges with stone, iron and steel structures. By the mid-1890s, the original bridge had become unfit for increasing traffic, and it was decided to replace the structure. In the spring and early summer of 1894, laborers from the Union Bridge Company delivered and erected the new steel bridge, and the original bridge was likely scrapped. Throughout the remainder of the 19th Century, the entire 20th Century and into the early 21st Century, the bridge remained largely unchanged, except for occasional upgrades to the timber pile trestle approaches and minor repairs to the remainder of the bridge. Prior to 2008, the bridge consisted of two 154-foot and one 153-foot, 6-panel, pin-connected Parker through trusses, set onto stone piers. Each end was approached by a lengthy series of timber pile trestle spans, set onto standard time pile bents. Like identical spans constructed for the BCR&N, Union Bridge Company fabricated the truss spans at their Athens, Pennsylvania plant. The stone piers are believed to have been constructed as part of the original contract for this line, which was awarded to the Iowa and Minnesota Contracting Company. A handful of different firms are known to have completed masonry for the initial construction of the BCR&M, and these firms likely joined to pool resources to form that contracting firm. Among the firms known to have constructed masonry for the BCR&M are the Dows, Ely & Company of Cedar Rapids, Iowa and O'Hanlon & O'Horn (also spelled O'Hara) of Cedar Rapids, Iowa. In particular, the later firm was recommended by the Chief Engineer of the BCR&M to communities in eastern Iowa due to the quality and timeliness of the masonry completed.

In the mid-1890s, the BCR&N ordered a handful of light Parker through trusses for use on their Burlington to Manly mainline, mainly to replace aging combination truss spans. These spans all used built-up members, a standard floor system and unique portal bracing. The top chord and endposts were both composed of built-up beams, constructed from two U-shaped channels connected by a solid plate on the top and V-lacing on the bottom. The bottom chord consisted of two different designs, with the outer two panels at each end using a built-up beam composed of two U-shaped channels connected by V-lacing on both sides. At the center two panels, the bottom chord consisted of three rows of rectangular eyebars. Unique to this bridge, the bottom chord was supplemented by an L-shaped bar, which was riveted to the built-up sections of the bottom chord and to the floorbeams. The vertical members were all composed of built-up beams, which used V-lacing on both sides. At the bottoms of the vertical members, the design changed to a solid I-beam, which was riveted to the floorbeams. All diagonal members were composed of eyebars, arranged into sets of two. The floor system was traditionally composed, consisting of heavy plate girder floorbeams at the panel points and two plate girder stringers. The floorbeams were notched at the ends, which slid over the bottom chord and connected to the vertical members. The lower lateral bracing consisted of L-shaped bars and square bars, some of which appeared to have been altered to strengthen the spans. The portal bracing consisted of a solid U-shaped plate, which had four sets of lattice in the middle. The sway bracing used a standard double intersection lattice design, with the center sway bracing thicker than the outer sway bracing. The upper lateral bracing consisted of V-laced beams, which were riveted to angled plates connected to the top chord. All of the piers used a standard rectangular shape with angled upstream noses. Stone for the piers consisted of a greyish limestone, possibly quarried near Anamosa, Iowa. The approach spans used a standard design, with stringers supported by standard bents. Several repairs were made to the bridge in the 20th Century, including replacing the tops of the piers with concrete, reinforcing the bases of the piers with sheet piling and placing iron bands around the northern two piers.

Additional identical spans were used at Cedar Rapids, Iowa (replaced in 1922) and north of Waterloo, Iowa (replaced in 2011). Parker trusses were first patented by Charles Parker in 1870 as an alternative to the Pratt truss pattern. At that time, iron was still an expensive building material, but was gradually becoming more economical. The main advantage of the design is a lighter top chord, due to the inclined shape. Parker trusses became popular for railroad use in the late 1880s, particularly for constructing longer spans while retaining a simple design. At the turn of the 20th Century, pin-connected trusses had largely fallen out of favor with railroads, and were superseded by riveted trusses. However, the Parker design remained popular for roadway use into the 20th Century, both with pinned and riveted connections. It is unclear why the BCR&N chose to use Parker truss spans in the mid-1890s, especially for short to medium through truss spans. By this era, traditional Pratt trusses would have been economical and strong enough for spans of this length.

In 1985, a majority of this line between Burlington and Cedar Rapids was abandoned. A short segment at Columbus Junction, including this span, were retained to access a Tyson plant north of the river. In June 2008, significant flooding struck along the Iowa River. On June 24th, 2008; a train was switching the Tyson Plant when the north approach trestle collapsed, sending the locomotive into the water. After the floodwater receded, a majority of the north approach was removed, leaving the remaining bridge abandoned. In 2014, the remainder of the bridge was completely removed. At the time of documentation, the truss spans and main piers appeared to be in fair condition, with some cracking noted to the stonework. However, the remaining timber approaches and timber deck were in poor condition. Significant portions of the former BCR&N route had been reused as part of the Hoover Nature Trail, and prior to its removal, this bridge would have made an excellent addition to the trail. Unfortunately, the removal of this bridge resulted in the loss of one of the more unique railroad truss bridges in Iowa, and one of the sole remaining truss bridges from the BCR&N era. The author has ranked this bridge as being regionally significant, due to the age, history and unique design.