Kinzie Street Railroad Bridge

View an article from The Journal of the Western Society of Engineers discussing the construction and design of the 1898 bridge (digitalized by Google)
View the Historic American Engineering Record documentation for this bridge
View an article from Engineering News describing the construction of this bridge
View an article from Railroad Age Gazette discussing the construction of this bridge

Located immediately south of Kinzie Street, this unique bascule bridge carries the original Chicago & North Western Railway (C&NW) mainline over the North Branch of the Chicago River. The location of the bridge is the location of a number of firsts in the City of Chicago. In 1832, a pedestrian bridge was constructed over the North Branch Chicago River south of Kinzie Street, and was the first permanent bridge across the North branch. In the late 1840s and early 1850s, the Galena & Chicago Union Railroad (G&CU) operated on the west bank of the North Branch Chicago River. By 1852, the railroad extended eastwards, constructing a swing bridge immediately downstream of Kinzie Street. The new bridge cost approximately $20,000, and a new station would be constructed along Wells Street, served by the bridge. This bridge would be the first railroad bridge in Chicago. The structure was constructed of wooden members, typical of early drawbridges in Chicago. Birds eye maps indicate that the bridge was likely a pony truss design. Throughout the mid-19th Century, traffic over the bridge continued to increase. It is unknown if the wood swing bridge was ever rebuilt between 1852 and 1879.

In 1879, the first bridge would be replaced by a new single track steel bridge. The new bridge would consist of a 175-foot, pin-connected bowstring pony truss swing span, set onto a stone pier. This span was fabricated by the American Bridge Company of Chicago, and was the first bridge to use steel. Another bridge along the Chicago & Alton Railroad at Glasgow, Missouri also claims to have been the first steel railroad bridge constructed, although the two structures were constructed concurrently. Due to byproducts in early steel, the 1879 bridge would be brittle, and would soon become too light for traffic. By 1897, the War Department conducted an analysis of the Chicago River and deemed the bridge a hazard to navigation. Throughout the 18-year life of the bridge, it had been struck, damaged and repaired numerous times.

In 1898, the C&NW began construction on a new steel bridge, constructed for two tracks. The new bridge would consist of a 195-foot, riveted quadrangular lattice through truss swing span, set onto stone a stone pier. The stone pier from the previous bridge was widened to accommodate the new span. The truss used features typical for the era, including laced members and a lattice, pedimented portal bracing. Construction on the bridge began in 1897, and the structure was completed in 1898. The truss span was fabricated by the Lassig Bridge & Iron Works, and the lattice design was reportedly chosen due to the redundancy of the members. It is believed that this was among the first lattice style swing spans constructed in the United States. The C&NW preferred this design, due to the durability and redundancy of the design. During the design of the 1898 bridge, it was important to construct the new bridge so that it would not interfere with the swinging motion of the Kinzie Street bridge upstream. This was accomplished by using an innovative roller, which placed the center of rotation under the south leaf of the swing span. The new swing span would be fabricated to the side, and the bridge would be installed in a 24-hour change out during March 1898.

By the turn of the 20th Century, the Wells Street Station had limited capacity, causing C&NW President Marvin Hughitt to consider reconfiguration the Chicago Terminal of the railroad. Up to 300 trains used the bridge every day, and the bridge opened on average 1,000 times per month for river traffic. The Wells Street Station was too small for the C&NW operations, and the bridge across the river severely restricted the ability of railroad traffic to reach the station. Constructing a new terminal within the "Loop" was not feasible, but a plot of land along the west bank of the South Branch Chicago River provided a suitable building ground for a new terminal. In 1905, consulting engineer John F. Wallace proposed a new station at the corner of Madison and Canal Streets. This new station would be approached by elevated viaducts, which would connect to the C&NW mainlines west of Ashland Avenue and north of Chicago Avenue. The new station would also eliminate the need for trains to cross the Chicago River, which would further increase service reliability. However, due to the costs, length of planning and amount of work needed to complete the project, the new station would not open until 1911.

During the early part of the 20th Century, the War Department began to request the removal of swing bridges from the Chicago River. Swing bridges greatly reduced the horizontal clearance for river traffic, and the center piers were often struck bt ships. In 1906, the War Department requested the replacement the C&NW bridge, as well as the adjacent bridge at Kinzie Street. C&NW engineers began to devise a replacement structure, and different proposals were initially made. One proposal involved replacing the bridge with a four track structure, consisting of two parallel bascule lift bridges. While this would not provide the same capacity as a new terminal on the west bank, the railroad felt that obtaining the necessary permissions to construct such a structure was critical in case plans for the Madison Street Terminal fell through. Preliminary replacement plans were made, and the plan approved by the War Department in October 1906. In December 1906, the Madison Street Terminal was authorized by the City of Chicago, ending any need for a four track bridge at this location.

Throughout 1907, plans were refined and the new bridge designed. Assistant Chief Engineer William H. Finley, who had overseen the construction of the 1898 bridge, would be tasked with overseeing the design and construction of the new bridge. The bridge design was limited to a bascule type bridge, where the span is rotated on a horizontal access. Due to constraints with the site, neither a traditional swing bridge or a horizontally translating span would fit into the location. While a vertical lift span was first used at Halsted Street in 1893, this design was not considered sufficient for railroad use at the time. After careful consideration of three different patented designs, the Strauss Bascule Bridge Company was retained to design a bridge utilizing the patented "Strauss trunnion" style bascule bridge. The use of an outside firm to design a movable bridge had become preferred by railroads in the 20th Century, as such structures became too complicated for already overworked railroad engineering shops to design. The design of the substructures was completed by railroad engineers. Contracts were let in 1907 to the Great Lakes Dredge & Dock Company for the construction of the substructures; to the Toledo-Massillon Bridge Company for the fabrication of the steel superstructure; and to the Kelly-Atkinson Construction Company for the erection of the new bridge.

During construction, railroad traffic still needed to use the bridge to access the Wells Street Station. Initial plans showed the large pier and counterweight located on the west bank, where it could be constructed without interfering with the existing swing span. Later in the design process, the design was changed to place the large pier on the east bank, where caissons could be sunk in a more reliable manner. However, the locations for the caissons was obstructed by the swing bridge whenever the bridge opened for river traffic, which could be as many 40 times per day. In response, the old bridge was partially disassembled, and a counterweight installed on the remaining portion of the shortened arm. This effectively formed a counterbalanced, or "bobtail" swing span. Work on modifying the existing bridge was completed through August 1907. Construction of the substructures began in December 1907. A large timber caisson was fabricated at the Goose Island yard of the Great Lakes Dredge & Dock Company. The large rectangular caisson measured 41 feet by 51 feet, and was illuminated by electric lighting. Workers removed soil from the caisson, until it descended 51 feet below the rivers surface to reach bedrock. A concrete mat was poured at the base of the caisson to seal it, and cylindrical concrete shafts were constructed within the caisson. Construction of the substructures was completed on May 17, 1908. Erection of the superstructure began shortly after completion of the substructure. One advantage of the Strauss bascule design is the superstructure could be erected in an upright position. Work on the new bridge was completed in September 1908; and the bridge opened to traffic on September 19, 1908. The old bridge was the demolished, and rebuilt to carry the Madison Division across the Kinnickinnick River in Milwaukee, Wisconsin.

The Kinzie Street Railroad Bridge consists of two spans. The main span consists of a 170-foot, 7-panel, riveted Warren through truss span, which is part of the Strauss trunnion bascule span. The east span consists of a 27-foot deck plate girder, which is located under the counterweight tower. The bascule leaf of the bridge runs at a 15-degree skew, and weighs approximately 800 tons. To accommodate the skew of the structure, the two truss lines are different lengths. The members of the truss are traditionally composed for the era, utilizing heavily laced members. The portal bracing of the truss consists of a solid beam, while the sway bracing utilizes a lattice design. The trunnion leaf (tower) of the bridge is connected to the bascule leaf by a large pinned connection, and also utilizes heavy built up members. The substructures of the bridge are all constructed of concrete. A large concrete block supports the east end of the bridge, while traditional concrete piers set onto timber piles hold the west end of the bridge.

During the 20th Century, Joseph B. Strauss became a principal designer of bascule bridges for railroads and roads throughout the United States. Strauss received his Civil Engineering degree in 1892, and began work at New Jersey Bridge & Iron Company. After a brief stint here, he came to Chicago in 1895, where he took a job with the Lassig Bridge & Iron Works. His work on movable bridges here, followed by work at the Chicago Sanitary District, allowed Strauss to take a position with Ralph Modjeski's engineering firm in 1899. By 1902, Strauss began his own firm, the Strauss Bascule & Concrete Bridge Company. In approximately 1910, the name was changed to the Strauss Bascule Bridge Company, to represent his focus on bascule bridges. During the early portion of his career, Strauss developed a number of different bascule bridge designs. The designs created by Strauss were patented, with much discussion in the engineering community about the ethics of patenting specific designs.

The Kinzie Street Railroad Bridge is an early example of a Strauss bascule span. Nearly all bascule bridges designed by Strauss had a fixed trunnion, where the weight of the structure was always delivered to the foundations at the same point. This design is in contrast to rolling bascule bridges, which rolls to lift and transfers the load to different parts of the foundation. The placement of the counterweights on the bridge also was innovative. To operate effectively, counterweights must balance the forces of the span through the entire path of motion. The Kinzie Street Railroad Bridge utilized a counterweight on top of the structure, and the trunnion on the upper chord. The counterweight tower on the bridge is constructed of a triangular shape, different from the rectangular shape used on earlier Strauss bascule bridges. At the time of completion, the bridge was the worlds longest and heaviest bascule bridge. This accomplishment would later be superseded by a number of other Strauss basule spans. The Kinzie Street Railroad Bridge can be considered a second step in bascule bridge design, and ideas used on this bridge eventually became standard design for later spans.

By 1911, the new Madison Street Terminal would open, and the bridge would no longer serve the volume of traffic it had previously served. The "low line" would become an industrial lead, mainly serving industries on the north bank of the Chicago River, and reaching Navy Pier. Throughout the 20th Century, railroad and river traffic at this location continued to fall. The second track was removed from the bridge prior to 1959. Today, the bridge is largely out of service, and has been placed in the raised position. Union Pacific Railroad operates a hi-rail truck over the bridge once per year, to prevent the bridge from being considered abandoned. It is currently unknown what will happen to the bridge, should it become abandoned. The bridge is considered a City of Chicago Landmark, and it is hoped that this status will preserve the bridge in the future. Overall, the bridge appears to be in fair condition, with some deterioration noted. The author has ranked this bridge as being highly significant, due to the design and history of this crossing.