Rock Rapids Railroad Bridge

Located on the south side of Rock Rapids, this attractive through truss bridge carries the former Illinois Central Railroad Sioux Falls Branch over the Rock River. When the railroad was first constructed at this location, the bridge consisted of a single through truss span, set onto timber pile piers and approached by timber pile trestle spans on either end. Many railroads commonly used this technique when first constructing new lines, as it allowed for approach embankments to settle without damaging expensive components of bridges. In 1897, the bridge was rebuilt with a new concrete pier and north abutment, and the north approach filled. The most recent upgrades to the bridge came in 1916, when the south approach trestle was rebuilt. Currently, the bridge consists of a 150-foot, 8-panel, pin-connected wrought iron Pratt through truss span, set onto a concrete pier and north abutment. The south approach consists of several timber pile trestle spans, covered by a ballast deck. Union Bridge Company fabricated the truss span at their Buffalo, New York plant; while G.H. Scribner constructed the concrete substructures. Timber components of the bridge were constructed by railroad company forces.

In the mid to late 1880s, the IC ordered a large quantity of truss spans from the Union Bridge Company for use on new branch lines and to replace existing light iron trusses. This bridge utilizes built-up vertical members, a traditionally constructed floor and a decorative portal bracing. The top chord and endposts are composed of built-up beams, with a solid plate on the exterior and X-lacing on the interior. The bottom chord is composed of eyebars, with two sets of two at the center panels and two sets of one at the outer panels. Vertical members consist of built-up beams, composed of tight X-lacing. The diagonal members consist of eyebars and use a rectangular shape. Similar to other truss spans from this era, the outermost lower connections use a double connection design, with a pinned connection located above and below the floorbeam. The floor is composed of two plate girder stringers, which are affixed to plate girder floorbeams. Additional bracing is present between the two stringers. The lower lateral bracing is composed of metal rods, which are looped at the end and pinned into the floorbeams. The upper lateral bracing consists of metal rods, and is affixed to the top chord. The portal bracing consists of a crested lattice beam with rounded lattice heel bracing. The sway bracing is composed of solid beams, which is connected to the vertical members by a rounded lattice heel bracing. The pier uses a standard rectangular shape, while the north abutment uses an elongated U-shaped design.

The Pratt truss design was the most popular railroad truss bridge design in the late 19th Century, as it was economical, durable and simple. However, the main limitation of this design was the length. In the mid-1880s, railroad spans of this design were generally limited to 200 feet or less, with most spans 150 feet or less. This bridge represents a typical sized span, and several similar examples were constructed for the IC. Since the original construction, it appears that no major alterations have been made to the bridge. After abandonment, the bridge was left intact and reused as an access driveway for the Rock Rapids wastewater treatment plant. As part of the conversion to a road, a new wooden deck has been added to the truss span. Overall, the bridge appears to be in fair to good condition, with the truss retaining a silver coat of paint and the concrete substructures having minimal scouring. The author has ranked this bridge as being regionally significant, due to the age and truss design.