CPKC Rock River Bridge (Rockton)

Located in Rockton, this pony truss span carries the former Chicago, Milwaukee & St. Paul Railway over the Rock River. The first bridges at this location were timber Howe through truss spans, set onto stone piers and approached by timber pile trestle. The trusses of this bridge were last renewed in 1889, and the approaches in 1896. By the 20th Century, wooden truss bridges had become obsolete for railroad use. In 1903, the trusses would be replaced with pony truss spans, and in 1906, the approaches would be replaced by deck plate girder spans. New concrete substructures were constructed with each of these projects. Currently, the bridge consists of a four standard 120-foot, 6-panel, pin-connected Pratt pony truss spans, approached by four 40-foot type "A" deck plate girders on the north end and one on the south end. The entire bridge is set onto concrete substructures, although it is unknown if the main piers of the bridge reused stone piers from the previous bridge. The truss spans were fabricated by the American Bridge Company, while the deck girders were fabricated by an unknown firm. Concrete work for the bridge was completed by Milwaukee Road company forces.

Typical of Milwaukee Road pony truss spans, the bridge consists of built-up lower and upper chords, solid beam compression members, bars for the tension members and an extensive use of gusset plates. In addition, the counter members utilize a turnbuckle, which allowed the members to be tightened. These types of spans were standard for the Milwaukee Road, and were designed under the direction of C.F. Loweth, Chief Engineer of the Milwaukee Road. Numerous examples of this design between 95 feet and 130 feet long were constructed throughout the Milwaukee Road system. These spans were popular, as they were strong, durable and easy to construct. Since the initial construction, it appears the bridge has been altered little, if any. Overall, the bridge appears to be in fair to good condition, with no significant deterioration noted. The author has ranked the bridge as being moderately significant, due to the truss design.