Keithsburg Railroad Bridge

View a news report about the 1981 collapse and demolition of the lift span

Located at the small town of Keithsburg, this large through truss bridge once carried the Minneapolis & St. Louis Railway over the Mississippi River. As the railroad network in southeast Iowa and west central Illinois was developed, it became clear that an additional crossing of the Mississippi River would be necessary. Existing crossings existed at Davenport and Burlington, leaving an 80 mile gap without a railroad bridge across the Mississippi River. A new railroad bridge at Keithsburg would be authorized in April 1882. Construction on the bridge began in 1885, and was completed by 1886. At Keithsburg, the Mississippi River is divided by Blackhawk Island, which creates a main channel on the east and a side channel (Blackhawk Chute) on the west. The first bridge consist of a 360-foot, pin-connected Whipple through truss swing span, a 255-foot, 13-panel, pin-connected Whipple through truss span and seven 205-foot, 11-panel spans of the same design. The east end of the bridge was approached by an 800-foot wooden pile trestle, and the west end of the bridge was approached by a 900-foot wooden pile trestle. Members of the bridge were composed of patented Phoenix Columns, The first bridge was designed by Sooysmith & Company, which also constructed the stone substructures. Phoenix Bridge Company completed the fabrication of the superstructure, which was constructed of wrought iron. Construction of the bridge was not without difficulty, with a number of different accidents delaying the project.

The first bridge was constructed at a time when railroad bridge designs were rapidly changing. The Whipple through truss design was popular in the 1870s and early 1880s for longer spans, particularly for lengths over 200 feet. A number of bridges using this design had been constructed across the Mississippi River, which required the use of larger spans. The main disadvantage of the Whipple design was the uncertainty of the stresses and strains in individual members, due to the double intersection design. However, this design fell out of favor by the early 1890s, as it provided significant uncertainty in the stress and strain of individual members. Between St. Paul and St. Louis, most early railroad bridges across the Mississippi River used swing spans, which rotated to allow river traffic to pass. However, by the early 20th Century, lift bridges were being developed, and would become the preferred movable bridge design of railroads. By 1907, the bridge had become too light for traffic, and the railroad began working on plans for a new bridge.

In 1908, the M&StL retained consulting engineers Waddell & Harrington to design a new lift bridge to replace the existing swing bridge. A novel lift span was designed, which affixed the towers to the outside of a fixed truss span, making it a vertical lift span. These towers were designed so that they could be moved to another fixed span if the navigation channel ever changed. Mcclintic-Marshall Construction Company was awarded a contract for the fabrication of the superstructure, and construction of the substructure was awarded to the Union Bridge & Construction Company, which also erected the new superstructure. The centerline of the new bridge would be placed approximately 60 feet upstream of the old bridge, and the fixed spans were designed to be positioned directly upstream of the existing fixed spans. Construction on the bridge was completed during 1909, and the old bridge was removed after the new bridge was complete. Due to the lightweight nature of the old bridge, it is believed that the old spans were scrapped upon removal.

As originally constructed, the bridge consisted of a 233-foot, 8-panel, riveted Pratt through truss lift span. This span was approached by a 115-foot, 4-panel span of the same design on the east end, on which the eastern lift tower was . In addition, nine 205-foot, 7-panel spans of the same design approached the lift span on the west side, and a 100-foot deck plate girder span served as the west approach. The entire bridge would be placed on concrete substructures, which are believed to have been constructed on caissons. The truss spans all used heavily built up members for the upper and lower chords and all truss web members, a traditionally composed floor and an A-frame portal bracing. As this bridge served the M&StL mainline, the superstructure spans would be heavily constructed. The lift span was operated by lift towers, affixed to the adjacent spans. These towers used a cable system and large concrete counterweights to raise and lower the bridge. A machinery house was located on the top of the east side of the lift span. As this bridge was an iconic structure for the small railroad, it was depicted in numerous promotional materials.

After the railroad was abandoned in 1971, the lift span was locked into open position to allow unobstructed river navigation. Proposals were made to use portions of the bridge as a barge loading facility, however these proposals never came to fruition. On June 30, 1981; four individuals ignited fireworks in the machinery house of the bridge, causing a fire. Grease from the east lift tower caught on fire, causing the cables to snap and the lift span to collapse. The east counterweight landed on the eastern span, severely damaging the outermost panel. The collapsed span blocked navigation, backing up dozens of tows and barges. On July 5, the lift span would be dropped to the river using explosives. During the demolition, the western counterweight and tower landed on the adjacent 205-foot span, collapsing that span as well. Wreckage of the bridge was quickly removed, and the river reopened to traffic by July 8. The pier between the lift span and adjacent west span was removed shortly after. Since then, the remaining spans of the bridge have sat abandoned, with the counterweight still crushing the east span.

Lift spans became popular for railroad use in the early 20th Century, as they were more cost effective, could be operated faster and allowed for a larger navigation channel. Vertical lift spans soon became the standard lift span design, as they were adaptable in numerous situations. Pratt trusses were the most common railroad truss bridge design in the late 19th Century, as they were durable, strong and simple. However, this design was largely superseded by riveted Warren trusses in the early 20th Century. A relatively small number of riveted Pratt trusses were constructed in the first decade. However, this bridge utilizes a heavily constructed version of the Pratt truss, likely due to the familiarity of the design to the fabricator, engineer and the railroad. As this bridge has been abandoned and partially demolished for over 40 years, it is unknown what the future is for this structure. Left to deteriorate, the bridge will undoubtedly need to be removed at some point. However, this would be an expensive task for a structure that is not currently posing a hazard to river traffic. Overall, the remainder of the bridge appears to be in fair condition. However, lack of access prevented the closer inspection of the condition of the remaining superstructure to assess the condition. The author has ranked this bridge as being regionally significant, due to the truss design. However, this ranking is diminished by the loss of the original lift span.