Glacial River Trail - Rock River Bridge

Located in Fort Atkinson, this large deck plate girder bridge carries the former Chicago & North Western Railway mainline across the Rock River. The first bridge at this location was likely a timber pile trestle, constructed when the line was first built. In approximately 1870, the bridge would be replaced by a wooden pony truss bridge, approached by a 15-foot stone arch span on the south end. The bridge was again rebuilt in 1883, using five 70-foot wooden Howe pony truss spans set onto timber pile piers. In 1900, the bridge was renewed with a similar structure. By the early 20th Century, wooden truss spans were no longer suitable for railroad use, and it was decided to replace the bridge with a steel and concrete structure. In 1911, the present deck plate girder bridge would be constructed, and the original south approach filled. The bridge remained in this configuration until approximately 2000, when it was converted to trail use. As part of the work, the original approach span was excavated, and a new 20-foot modern concrete arch span constructed to connect the deck plate girder and stone arch sections, giving the bridge its present configuration.

Currently, the bridge consists of five 60-foot deck plate girder spans, set onto concrete substructures. The south end of the bridge is approached by a 20-foot modern concrete arch span and a 15-foot stone arch span. The deck plate girders use two slightly different designs, with the southern three spans (spans #1, #2 and #3) using larger center panels and closely spaced stiffeners at the ends, while the northern three spans (spans #4 and #5) use more evenly sized stiffeners. All five spans use a standard design, with two heavy plate girders and an open deck. The stone arch span uses a standard design, with a semi-circular arch and no wing walls. Unique to this span, the top longitudinal courses of stone are stepped, making the deck wider than the arch. Stone for this span was quarried at an unknown location, and consists of a white colored limestone. The modern concrete arch span uses a decorative design, with a shallow arch and ribs on the exterior. The concrete substructures use a standard design, with diamond shaped piers and standard abutments consisting of sloped wing walls. The southern three spans were fabricated by the Wisconsin Bridge & Iron Company in 1911, while the northern two spans were originally fabricated in 1899 by the Lassig Bridge & Iron Works for use at an unknown location before being moved here in 1911. An unknown contractor constructed the stone arch span, while an additional unknown contractor constructed the concrete substructures. The concrete arch and conversion to a trail was also completed by an unknown contractor. Deck plate girder spans were commonly used by railroads, as they were durable and easy to construct. A number of early bridges along this line used stone arch spans for approaches, as it helped stabilize the approach embankments. Since the initial construction, the only significant alteration to the bridge includes constructing the concrete arch span and the addition of a concrete deck and railings. The bridge now carries the Glacial River Trail, and is part of an attractive park in the area. Overall, the bridge appears to be in fair to good condition, with no significant deterioration noted. The author has ranked this bridge as being moderately significant, due to the stone arch span and relocation history of two spans.