Sangamon Valley Trail - Sangamon River Bridge

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Located northwest of Springfield, this massive deck truss bridge carries the Sangamon Valley Trail (former Chicago & North Western Railway) over the Sangamon River. Initially, the bridge was constructed in 1912 using five deck truss spans, set onto concrete piers. While the line was originally constructed for a single track, the piers were constructed for a second track, although this was never constructed. The initial structure was approached by lengthy timber pile trestle approaches on either side. Timber approaches were used extensively on this line, particularly at bridges located on large embankments. These temporary approaches allowed the embankment to settle without damaging or destroying concrete substructures. By the early 1920s, most of the temporary approaches on this line had been replaced with permanent construction. In 1921, the entirety of the timber approaches were replaced with steel deck plate girder spans, set onto additional concrete substructures. In approximately 1975, the north end of the bridge was damaged by a derailment, and the northern span was replaced by a steel stringer span, giving the structure its current configuration.

Currently, the bridge consists of five 150-foot, 7-panel, riveted double intersection Warren deck truss spans (spans #2-#6), which were part of the original bridge. The bridge is approached by a single 60-foot deck plate girder span (span #1) on the south end. In addition, the bridge is approached by three 85-foot deck plate girder spans (spans #7-#9) and a 40-foot steel stringer span (span #10) on the north side. With the exception of the northernmost pier (pier #9), all substructures of the bridge are constructed of concrete. The piers for the approaches were only constructed for a single track, and the northern pier uses stacked beams to support the northern span. Piers supporting the truss spans were constructed by the Cleary-White Construction Company, which had the contract for concrete work on the new line. The remaining piers and both abutments were constructed by an unknown contractor. Because the bridge was built at a number of different times, the bridge has a number of different builders, designs and unusual features.

The truss spans were all fabricated by the King Bridge Company, and use a variation of the standard C&NW deck truss design from the era. These spans are comprised of deep trusses, heavily constructed members and a traditionally composed floor. Newer stringers appear to indicate that these spans were rebuilt at some point in the second half of the 20th Century. The lower and upper chord are both constructed of built-up members, and an additional rolled vertical member connects the intersections to the upper chord. The 60-foot deck girder span (span #1) and south 85-foot deck girder span (span #7) were fabricated in 1921 by the Wisconsin Bridge & Iron Works, and were part of the first reconstruction project. Both these spans use a standard design, with heavily constructed bracing and deep plate girders. Spans #8 and #9 and were installed as part of a second reconstruction project, which was authorized soon after the first project. Span #8 was fabricated in 1921 by the American Bridge Company, and is similar to span #7. Span #9 appears to have been reused here from an unknown location. This span appears to have been fabricated in approximately 1910, and has a missing plaque that cannot be identified, as well as faded stenciling which reads "Mfg. Co.". Span #9 appears to have been heavily modified upon relocation here, with new plates, lateral bracing and webbing. In addition, a number of plates have been welded over the outside of the girders and empty rivet holes are present inside the structure. The ends of this span use a rounded end, which has been rebuilt with additional steel to make a squared end. This possibly indicates that this span was originally a through girder, which was reconstructed into a deck girder. The steel stringer span (span #10) was likely reused here from an unknown location, and appears to have originally been fabricated in approximately 1930. This span uses a standard design, including four beam lines connected by a typical bracing. It is also unknown if the steel blocking on the north pier is original to the 1921 reconstruction, or if it was installed after the north span was installed.

Railroads often reused bridge spans, as it provided a cost effective way to replace and maintain bridges without requiring large amounts of new steel. These spans were often rebuilt and modified to meet the requirements of the new location. The C&NW used this practice extensively, preferring to reuse spans where feasible. Lattice truss spans were rarely used by railroads in the United States, as traditional Pratt or Warren spans were more economical, easier to construct and had more predictable stresses within the structure. While most railroads avoided the use of lattice spans, the C&NW used the design nearly exclusively between the late 1870s and early 20th Century. The C&NW believed that the design provided greater redundancy in the event of a collision or derailment. Dozens of examples of different lattice style truss designs remain in use today along former C&NW lines. In 2017, the bridge was rehabilitated and opened as part of the Sangamon Valley Trail. As part of the rehabilitation, the original railroad deck was removed from the structure and a new wooden deck installed. Overall, the bridge appears to be in fair to good condition, with no significant deterioration noted. The author has ranked this bridge as being highly significant, due to the size, variety of designs and extensive history of the spans.