WSOR Rock River Bridge (Horicon)

Located in Horicon, this unique deck plate girder bridge carries the former Chicago, Milwaukee, St. Paul & Pacific Railroad over the Rock River. The first bridge at this location likely consisted of a timber pile trestle, constructed when the line was first built. Because early timber bridges used untreated timber, these structures were susceptible to quick deterioration. In 1862, the original bridge was replaced by two wooden Howe deck truss spans, set onto new limestone abutments and a pier. It is likely that this bridge was updated at least once in the 19th Century, likely with a similar design. By the early 20th Century, the Milwaukee Road was working to replace timber bridges with steel and concrete structures. In 1911, the present structure would be constructed at this location, using iron girders reused from other locations. Currently, the bridge consists of a 66-foot and a 55-foot deck plate girder span, approached by two 15-foot concrete slab spans on the east end and two 18-foot concrete slab spans on the west end. The bridge is set onto concrete substructures, and reused the stone abutments from the 1862 bridge. The iron girders were all fabricated by unknown contractors, while the alterations and concrete substructures were completed by railroad company forces.

The eastern span consists of a 55-foot deck plate girder span, constructed with four girder lines. Two of the girders were reused from Bridge #B-10 across the Menomonee River near Milwaukee, Wisconsin, and were originally fabricated in 1888 by an unknown contractor. The other two girders were reused from Bridge #E-398, located across Johnson Creek near Thompson, Illinois; and were originally fabricated in 1895 by an unknown contractor. The western span consists of a 66-foot deck plate girder span, constructed with three girder lines. Two of the girders were also reused from Bridge #B-10; while the center girder was reused from Bridge #B-6; also across the Menomonee River in Milwaukee. The single girder from Bridge #B-6 was salvaged after one of the five spans was damaged during disassembly. This structure was originally fabricated in 1883 by an unknown contractor. The other four girders from Bridge #B-6 were ultimately reused at Bridge #Q-190, while additional girders from Bridge #B-10 were ultimately reused at Bridge #P-310. When the girders were relocated to this location, they were heavily modified, with new internal bracing installed. All girders are believed to be constructed of wrought iron, the typical material for bridges from this era.

Railroads often reused iron and steel spans, as it provided a cost effective way to replace bridges on branch lines without requiring large amounts of new material. In particular, the Milwaukee Road was particularly crafty, combining scrap pieces from different bridges to make a stronger span. One method the Milwaukee Road used to accomplish this was to rebuild spans with additional girder lines, allowing for greater loading capacity. These alterations typically involved disassembling the original material, drilling new holes and installing new bracing. In addition, the Milwaukee Road was well known for constructing their own concrete bridges. This allowed the Milwaukee Road to keep a skilled group of laborers on staff, which could construct entire bridges. Many of the Milwaukee Road bridges were designed in house, including the original iron construction, alterations and substructures. Since the initial construction, the bridge has seen few alterations, although the original concrete ballast deck has been replaced by a timber ballast deck. Currently, the bridge remains in regular use. 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 ages and histories of the girders used to construct the main spans.