DREI Lake Decatur Bridge

Located on the east side of Decatur, this deck plate girder bridge carries the former Baltimore & Ohio Railroad over Lake Decatur along US Route 36. Little is known about the history of this bridge. It is believed that the first bridges at this location were likely constructed of timber, and possibly were timber truss bridges. In the late 1880s, a number of upgrades were made to this line, and it is believed that this bridge was replaced by an iron truss bridge. This bridge lasted until approximately 1915, when it would be replaced by three deck plate girder spans, set onto concrete piers and approached by timber pile trestle spans. In 1922, the timber approaches would be replaced by an additional deck plate girder span on either end. As part of the 1922 reconstruction, a secondhand span was reused from an unknown location for the east span. This reconstruction was likely completed in response to the impounding of the Sangamon River to form Lake Decatur, which was completed that year.

Currently, the bridge consists of three 73-foot deck plate girder spans, a 40-foot west approach span and a 50-foot east approach span. The four piers of the bridge are constructed of concrete, while the abutments are both constructed of timber piles. All of the deck plate girder spans use a traditional design, with heavy girders connected by interior bracing. The three main spans are heavier than the outer spans, likely due to the longer length. It is unusual for steel spans to use timber abutments. However, this design may have been chosen due to the close proximity of the The three main spans were fabricated by an unknown contractor, and the concrete substructures were constructed by another unknown contractor. The west span was fabricated by the McClintic-Marshall Corporation, and appears to have been installed new at this location. The east span was fabricated in September 1889 by the Smith Bridge Company, and was reused from an unknown location. None of the spans appear to have had any significant modifications since they were installed here.

Railroads often reused steel spans, as it provided a cost effective way to upgrade bridges on branch lines without requiring significant amounts of new material. Typically, these steel spans were repaired prior to being installed. It is likely that the east span was reused from a location in Indiana or Ohio, and was probably constructed during the large bridge upgrade programs in the late 1880s. Because the span was installed in 1922, it is likely that the span was originally fabricated for the C&IW. It is unknown if this span came from a single structure, or was part of a multiple span structure. The Smith Bridge Company was not known to have constructed a large amount of railroad spans, and instead seems to have primarily focused on roadway spans. Since the 1922 reconstruction, the bridge appears to have remained largely unchanged. 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, mainly due to the age and builder of the eastern span.