Wells Street Bridge

View an article describing the construction of this bridge
View an article describing the construction of this bridge
View an article describing the construction of this bridge
View the Historic American Engineering Record documentation for this bridge

Located near the confluence of the North Branch and South Branch of the Chicago River, this iconic double deck bascule bridge carries Wells Street and the CTA Brown and Purple Lines over the Chicago River. The present bascule bridge is the eighth bridge at this location. The first bridge at this location opened in 1841, and consisted of a wooden swing bridge, which used a pontoon design to swing instead of a center pivot pier. The bridge was built by John Van Osdel, and operated by hand. The bridge was replaced by the second structure in 1847, which used a similar design. A third bridge was constructed in 1849, again using a pontoon style swing span. In 1856, the bridge would be again rebuilt with a wooden swing bridge. This structure used a stone center pivot pier, and was constructed by Derastus Harper. A fifth bridge was completed in 1862 by Fox & Howard, using a similar design. The fifth bridge was destroyed during the Chicago fire in 1871, and was rebuilt in 1872. The 1872 structure consisted of an iron truss swing bridge, set onto a stone pier. This bridge used a light design with a curved top chord, and was also constructed by Fox & Howard.

By 1888, a stronger bridge was desired to carry Wells Street. Keystone Bridge Company was contracted to fabricate a new 220-foot long iron swing bridge, which would sit on a new center pier. The seventh bridge utilized a pin-connected Pratt through truss design, with a curved top chord. The swing mechanism of the seventh bridge was powered by steam. Streetcar tracks were also added to the seventh bridge, and carried a predecessor of the Chicago Surface lines. In 1896, the seventh bridge was heavily reconstructed, including adding a third truss line and an upper deck. This work was completed in conjunction with the construction of the Northwestern Elevated Railroad, which would use the upper deck of the bridge. Due to the large volume of railroad traffic, this arrangement did not work well for the railroad, as the bridge was required to open and close several times through the course of a day. In addition, the bridge impeded river traffic, due to the location of the center pier. In the late 1890s, the Army Corp of Engineers studied the bridges throughout Chicago to facilitate improvements for river traffic. Swing bridges were identified as being unacceptable to cross the river, due to the navigation constraints.

The seventh bridge was originally designed for light vehicular traffic. By 1916, the bridge had proved completely unacceptable for the traffic it was carrying. Plans for a new bridge were prepared that year, and the replacement was authorized later in 1916. As part of the agreement, the elevated railroad, the streetcar company and the City of Chicago were each required to pay for one third of the cost of a new bridge. The chosen design was a double-deck fixed trunnion bascule bridge, similar to other another bridge at Lake Street, which had been completed in 1916. The plans for the bridge were prepared by Hugh E. Young, Engineer of Bridge Design for the City of Chicago. In addition to using a city-designed structure, a license was obtained from the Strauss Bascule Bridge Company. This license allowed the city to add patented members to the bridge, which resulted in a modified design from other city-designed structures. As part of the construction, it was paramount to avoid disrupting traffic along the elevated railroad line. Thomas G. Pihlfeldt, who had managed the construction of the nearby Lake Street Bridge, decided to use the same methods as the construction of the Lake Street Bridge. Pihfeldt aimed to further minimize outages and delays, with the goal of improving the sequence and timing of construction.

Construction on the new bridge began in May 1917. Construction began with the foundations and tailpits. The main spans of the bridge would be supported by a transverse shaft known as a trunnion, which the leaf rotates about; and the trunnion would be supported on massive columns and girders in a tailpit. The tailpits would resemble massive hollow piers, and were to have dimensions of 48 feet by 48 feet, with a depth of 30 feet inside. The base of the walls for the tailpit were designed to be 10 feet thick, and the top of the walls were designed to be 5 feet thick. The primary function of the tailpit would be to house the operating machinery and counterweights of the two leaves. Cofferdams were constructed under the street-level plate girder approaches of the old bridge to facilitate the construction of the tailpits, piers and abutments. The tailpits would be set onto six large cylindrical piers, which were filled with concrete. The piers were arranged in three sets of two; with one set supporting the river side of the tailpit, one set supporting the trunnions, and a third set supporting the columns. Due to the swampy nature of the area surrounding the Chicago River, the piers were originally planned to be sunk a staggering depth of 178 feet to reach solid bedrock. However, the plan was revised to install the piers to a depth of 75 feet below the water surface. The river piers would be 11 feet in diameter, reaching 19 feet in diameter at the bottom. The trunnion piers would be 10 feet in diameter, and enlarged to 18 feet in diameter at the bottom; and the anchor piers would range from 7 feet to 12 feet in diameter. The tailpit and substructures were constructed using heavily reinforced concrete, which used extensive longitudinal and transverse steel bars. Work on the piers and north tailpit were completed in April 1919; followed by the north abutment in May of that year. Work then began on the south substructures, which were completed in October 1920.

In 1917, construction of the bridge was complicated due to the entry of the United States into World War I. Labor strikes, material shortages and cost increases proved to be detrimental to the project, and the city soon began to exhaust funding for the bridge. In addition, the Northwestern Elevated stated that the company would only pay their share upon completion of the new structure. Work was stopped in April 1921, forcing the city to sell bonds to cover the cost of the bridge. By this point, the substructures and tailpits of the bridge had been completed. Once funds were again available, work resumed on the bridge. Laborers worked rapidly to assemble the new superstructure in a raised position at each end of the bridge. The roadway deck of the old bridge closed to traffic in September 1921, and the new approaches were installed. A change-out of structures was planned for the weekend of December 2nd, 1921; which would minimize closures to a single weekend. At 7 PM on Friday night, work crews closed the old bridge, and removed the elevated rails. Laborers worked around the clock to carefully cut away the center portion of the old swing bridge, and lowered the new bridge into place. By the end of December 1921, the new bridge was carrying traffic; and the work was completed in its entirety by early 1922.

The bridge consists of a double deck Warren through truss bridge, which carries Wells Street on the lower level, and the two elevated railroad tracks on the upper level. Typical of bridges in Chicago, the bridge consists of a double leaf fixed trunnion bascule span, where the two halves of the bridge rotate upon their endpoints. The trusses are spaced at 42 feet apart, and the deck of the bridge is 72 feet wide. The bascule span measures 268 feet from center to center of the trunnions. Each leaf of the bridge consists of a 172-foot, 11-panel riveted Warren through truss, which are cantilevered from the ends. While much of the truss is traditional in composition, the ends of the lower chords are curved, which help carry the counterweight of the leafs. The ends of the spans consist of a 48-foot carrying truss, and a machinery girder. The machinery girders were constructed by using a patented design, created by the Strauss Bascule Bridge Company. The ends of the spans are located over a large concrete pit, known as a tailpit. This pit allows the bridge to rotate, and holds the machinery. The carrying trusses carry the entire dead load of the bridge. In addition, the bridge utilizes decorative concrete substructures, and machinery houses are located on the northwest and southeast corners of the bridge. Similar to other lift bridges in Chicago, these machinery houses are constructed of concrete and glass, and add to the aesthetic of the bridge. Members of the trusses are constructed of built up members, which utilize heavy lacing. The roadway floor of the bridge is constructed of an open grate deck, which was often used on city owned lift bridges. When completed, this bridge was the first double deck bascule bridge completed.

Throughout Chicago, this design of bridge was popular for city owned crossings of the Chicago River. The design provided a design that was both functional and aesthetic. Since the initial construction, the bridge has seen a number of modifications. The original deck was replaced after the streetcar line was removed. Other repairs have been made to the bridge over the years, including the reconstruction of the south end elevated railroad approach viaduct, which was reconstructed with a pony truss span in the 1980s or 1990s. A significant rehabilitation project in 2013 replaced the inner five panels of each leaf with new steel, which was fabricated using the same design as the original members. The remainder of the bridge was rehabilitated, and replicas of the original decorative handrails were installed on the bridge. Overall, the bridge appears to be in good condition, and should continue to reliably serve traffic for years to come. The author has ranked this bridge as being regionally significant, due to the unique design of the bridge. Despite the large quantity of similar spans in Chicago, relatively few exist on a national scale. In addition, double deck versions of this type of bascule bridge are only found in Chicago. In addition to this bridge, similar double decked bridges are used at Lake Street, Michigan Avenue and Lake Shore Drive.