Deering Bridge

View an article discussing the construction of this bridge

View an article discussing the construction of this bridge (digitalized by Google)

Located upstream of Ashland Avenue, this iconic bascule bridge carries the Union Pacific North line over the North Branch Chicago River. The first bridge at this location was a timber swing bridge. In 1887, the bridge would be replaced by a double track 176-foot through truss swing span, set onto stone substructures. This swing span utilized a Pratt design with pinned connections and light members. During the late 1890s, the C&NW elevated the Milwaukee Division between Sangamon Street and Balmoral Avenue, constructing a third track. The old bridge was raised in 1900 to accommodate the track elevation, but remained a bottleneck for the railroad. By the early 1910s, the 1887 bridge had become too light for traffic, and the railroad decided to replace the bridge. Strauss Bascule Bridge Company was retained to design a new three track bascule lift span to replace the swing span. The design and contracting was overseen by W.H. Finley, Chief Engineer of the C&NW. American Bridge Company was contracted to fabricate the steel superstructure; Great Lakes Dredge & Dock Company was contracted to construct the concrete substructures and remove the old bridge, and the Kelly-Atkinson Construction Company was contracted to erect the new bridge.

Due to the volume of commuter traffic serviced by this line, extended closures of the bridge were not permitted. Temporary trestles were constructed as to not interfere with railroad operations. The cylinders for the piers were constructed using ordinary pneumatic methods, although compressed air was not necessary. The superstructure of the bridge was erected in the upright position, which did not interfere with railroad traffic. Because of the elevation differences of the old and new bridges, the north approach girder could not be constructed until the old bridge was removed. To solve this problem, it was decided to swing the old bridge to open position, remove the middle of the swing span, and lower the new bridge. Work on changing the spans was begun at 12:30 am on Sunday, July 31st 1916; when the old bridge was closed to traffic and the obstructing portion of the bridge cut out of the way. While the old span was being removed, the railroad company erected the north approach of the bridge. The bridge was lowered for the first time at 9:45 the same morning, and opened to traffic at 6:00 PM that evening. The remainder of the old bridge was then removed for scrap.

The bridge consists of a 180-foot Strauss heel trunnion bascule bridge, which utilizes an 8-panel, riveted Warren through truss design. A large concrete and steel counterweight extends from the south side of the span, utilizing large concrete slabs set parallel to the tracks. A 54-foot deck plate girder span is located underneath the counterweight, and a 35-foot deck plate girder approaches the north end of the bridge. The truss span utilizes a typical design for the era, with heavy members, riveted connections and a deep floor. Due to the angle of the river, the north end of the bridge is set at a 16 degree skew. The east face of the truss span is 174 feet long, and the west face of the truss span is 186 feet long. The counterweight truss is supported on a tower constructed of two triangular frames, and the counterweight is set 55 feet behind the main trunnions. A total of 1,263 tons of structural steel were required for the bridge. The substructure of the bridge consists of concrete abutments, and the north pier consists of two concrete cylinders joined by a concrete beam. The trunnion on the south side of the bridge rests on four cylinders, which are joined by lattice beams.

A number of bascule bridges were constructed for railroad use in Chicago, owing to the nature of the rivers within the city. This design provided a clear channel for the river below. In addition, the design was compact, and provided a structure which could be integrated into urban settings. Joseph B. Strauss developed a revolutionary design, known as the trunnion bascule bridge. A trunnion is a short shaft, on the "leaf", or movable section of the bridge rotates. A heel trunnion type bridge utilizes the trunnion at the connection between the inclined endpost and the lower chord. This particular design was first constructed in 1910, and was used at several locations throughout the United States. Throughout the early 20th Century, Strauss would sell municipalities and railroads on the benefits bascule design as opposed to swing or lift bridges. Later in his career, Strauss would become renowned for his work on the Golden Gate Bridge. Numerous bridges throughout Chicago were designed by his firm.

Since the initial construction, the bridge has seen a number of changes. The third track was removed in the 1980s, leaving two tracks in use. A major rehabilitation was done on the bridge in 2018, when the deck plate girder north approach was replaced, and numerous other repairs made to the truss. It also appears that the bascule span is no longer capable of being operated. Despite these alterations, the bridge retains a high level of historic integrity. Overall, the bridge appears to be in fair to good condition, with no significant deterioration noted. It is unknown if a third track will be installed on the bridge in the future. The author has ranked the bridge as being highly significant, due to the design.