Sangamon Valley Trail - Spring Creek Bridge

View historic articles discussing the construction of this line (digitalized by Internet Archive)

Located on the west side of Springfield, this historic deck truss bridge carries the Sangamon Valley Trail (former Chicago & North Western Railway) over Spring Creek. The first bridge at this location consisted of a 60-foot deck plate girder span, supported by timber pile piers and approached by timber pile trestle spans on either end. 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 1920, the first of two projects was authorized to reconstruct the bridge. As part of this project, a lattice deck truss span would be installed, a concrete skeleton abutment constructed on the south end, and the 60-foot span shifted to the north side of the truss, supported by a steel bent. This second iteration of the bridge retained a lengthy pile trestle approach on the north end. Work on this project was completed in early 1921. A second project was authorized in 1921, and involved the replacement of the remaining pile trestle with two additional deck plate girder spans and shifting the 60-foot span to the far north end of the bridge. New concrete piers and a north abutment were constructed at this time, giving the bridge its current configuration. Work on the second project was completed in August 1922. Upon completion of the second project, the steel tower from the 1919 structure was installed at Bridge #403 near Wrightstown, Wisconsin; where it continues to serve traffic.

The bridge consists of a 119-foot, 10-panel, riveted quadruple intersection lattice deck truss span, approached by two 85-foot and one 60-foot deck plate girder span on the north end, and a concrete skeleton abutment consisting of three 11-foot bays on the south end. The entire bridge is set onto concrete substructures, which were likely constructed by two separate unknown contractors. The lattice deck truss span was originally fabricated in 1883 by the Alden and Lassig Bridge & Iron Works, and was originally part of a bridge at Geneva, Illinois. The two 85-foot spans were fabricated in 1921 by American Bridge Company, and the 60-foot span was fabricated in 1912 by the King Bridge Company. The south approach uses a variation of a skeleton abutment design, which uses longitudinal concrete arches to support a large concrete slab. Skeleton abutments were occasionally used by railroads to help stabilize troublesome embankments. Often, these large concrete structures were required to be constructed monolithically. The south approach on this bridge appears to have been constructed monlithically, and consists of a superstructure, abutment, three bents and a large concrete pier at the truss span.

The Geneva bridge originally consisted of two 125-foot (spans B and C) and two 119-foot (spans A and D) double track iron lattice deck truss spans, each containing two outer "light" truss and one "heavy" center truss. Upon replacement of that bridge, the trusses were shipped to the bridge yard in Chicago. Here, all portions of the original structure were scrapped except for the trusses and outer cross frames. The two heavy 119-foot trusses were reconstructed into a single span, and installed at this location. During the reconstruction, the lateral bracing, interior cross bracing and floors were reconstructed with new material. The remaining trusses from the Geneva bridge were reused at the nearby Lick Creek Bridge, and were rebuilt in a different manner. The span on this bridge is unique, as it only uses two truss lines, although these truss lines were originally part of different spans.

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. The rebuilt truss span used for this bridge represents an innovative way of maximizing the value of secondhand bridge spans. 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. This span uses a quadruple intersection design, indicative of an earlier span. Later spans moved to triple and eventually double intersection variations. ln 2011, 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 steel 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 history and design of the structure.