Name | Sylvan Island Railroad Bridge Chicago, Burlington and Quincy Railroad Bridge #251.05C |
Built By | Chicago, Burlington & Quincy Railroad |
Currently Owned By | MidAmerican Energy |
Superstructure Contractor | Detroit Bridge & Iron Works of Detroit, Michigan |
Design Engineer | Thomas C. Clarke |
Length | 195 Feet Total |
Width | 1 Track |
Height Above Ground | 15 Feet (Estimated) |
Superstructure Design | Whipple Through Truss |
Substructure Design | Stone Masonry and Concrete |
Date Built | 1893 Using a Span Fabricated 1867 |
Original Location | Bridge #204.66; Mississippi River Bridge; Burlington, Iowa |
Traffic Count | 0 Trains/Day (Bridge is Closed to Traffic) |
Current Status | Closed to Traffic |
Chicago, Burlington & Quincy Railroad Bridge Number | 251.05C |
Significance | National Significance |
Documentation Date | 1/27/2018; 9/2/2023; 4/13/2024 |
In the early 1890s, the Sylvan Steel Works developed a large iron works complex on Sylvan Island, located between Arsenal Island and Moline. In 1893, the Chicago, Burlington & Quincy Railroad (CB&Q) and Chicago, Rock Island & Pacific Railway jointly constructed a short spur to serve the island. A new bridge would be required across Sylvan Slough, the southern border of the Island, and the present bridge was constructed that year. The CB&Q provided a secondhand iron truss bridge, reused from the recently replaced Mississippi River Bridge at Burlington. The truss span was shipped to Sylvan Island, and installed on new stone abutments. The abutments were partially encased in concrete in 1900, giving the structure its current appearance.
Currently, the bridge consists of a 195-foot, 15-panel, pin-connected Whipple through truss span, set onto stone and concrete abutments. Originally constructed in 1867, the truss span was designed by Thomas C. Clarke and fabricated by the Detroit Bridge & Iron Works. The Burlington Bridge originally utilized a through truss swing span, 175-foot and a 200-foot Whipple through truss spans on the west side and six 250-foot, 19-panel spans on the east side. It is believed that the span over Sylvan Slough was reused from one of the 250-foot spans. Upon installation here, the span was shortened from a 250-foot span by removing four panels from the center of the span. At that time, additional repairs were made to the structure, including replacing the original stringers with timber and strengthening the connections. The superstructure is composed of a cast iron top chord, and the vertical members and endposts of the bridge are comprised of patented wrought iron Phoenix Columns. The lower chords and tension of the bridge are comprised of slender bars, which are looped around the connections. The portal and sway bracing of the bridge utilizes angled bars, typical for early CB&Q bridges.
As iron bridges became the standard in the 1860s, numerous designs were used. Several unique designs are displayed on this structure. The upper chord consists of a tubular cast iron shape, set in an octagonal cross sectional shape. This upper chord contains an angle at each end, which the endpost is slid into. The tension members of the truss utilize a bolted connection, which is slid through forged openings in the upper chord. The lower portion of the tension member uses a forged loop at the connection, known as a link. The lower chords consist of wrought iron links, an early design for members at pinned connections. Later designs used eyebars, which were forged with the member. The vertical members are comprised of Phoenix Columns, with a large shoe-like coupling on the bottom. This coupling covers the pin at the connection, which runs through a hole in the coupling. The tops of the vertical members use a flat plate, which is connected to the upper chord by bolts. These rods are set on the coupling, but are not connected. The floorbeams are held to the truss by iron rods, which form straps around the bottom of the beam. A lower lateral bracing consists of two parallel rods, which are inserted through forged openings in the coupling and bolted at the end. Floorbeams of the bridge consist of I-beams, which may not be original 1867 material. The stringers are set onto the floorbeams, and a wooden shim is used between the floorbeam and stringer.
The use of cast couplings is a very rare feature of this bridge. Very few examples of this design were used in the United States. The main disadvantage of this design was the use of a single cast member exposed to large forces. Defects in the iron of the coupling could cause cracking, and cause the entire span to fail. Cast iron was used in early bridges, but was quickly replaced by wrought iron. Cast iron is more brittle and more susceptible to defects. Phoenix Columns were patented by Samuel Reeves in 1862, and are comprised of segments riveted together to form a hollow tube. These types of members were an innovation not just for bridge building, but also for the construction of taller buildings. These members demonstrated a high level of strength while reducing the dead load of the structure.
The Mississippi River posed a formidable barrier for railroads looking to expand west. The earliest bridges across the Mississippi River, completed in the 1850s and early 1860s, were largely constructed of wooden trusses. By the mid-1860s, iron bridges had been developed to provide long spans and carry heavy loads. The bridge at Burlington was among the earliest iron bridges constructed across the Mississippi River, and represented a significant achievement for the railroad. Early iron bridges quickly became too light for mainline railroad traffic, and most iron spans were replaced by heavier steel spans in the 1880s and 1890s. While these spans were too light for mainline traffic, they could feasibly be reconstructed, strengthened and reused to serve branch lines, spurs and roadway overpasses. Railroads often sought to save costs on bridge reconstruction, reusing spans where possible. Four additional spans from the original Burlington Bridge were reused as part of an overpass at Laramie Avenue in Chicago, which has since been replaced. The remaining 175-foot, 200-foot and 250-foot spans were also likely reused, although the locations are unknown. An identical bridge at Quincy, Illinois used the same design, and the components of that bridge were also likely reused.
A number of alterations appear to have been made to the span since the installation here. Additional high strength members have been added to reinforce the lower chord. The hip vertical members been encased with a built up beams, likely completed after the bridge was moved here. Despite the numerous alterations, the bridge retains a great level of historic integrity. Very few iron truss bridges from the 1860s and 1870s continue to survive today. Even fewer of these spans use cast iron or other unique design features seen on this bridge. In the mid-20th Century, Republic Steel, which acquired the Sylvan Steel Works closed the foundry at Sylvan Island, and the bridge would be abandoned. After the bridge was abandoned, a wooden deck was added for automobiles to cross the bridge. The bridge has since been acquired by Mid-American Energy, which has fenced the bridge off. Overall, the bridge appears to be in good condition, with no major deterioration noted. The author has ranked this bridge as being nationally significant, due to the design, materials, age and high level of historic integrity retained in this structure.
Citations
Build dates and relocation history | Chicago, Burlington & Quincy Railroad Valuation Summary at the Newberry Library |
Builder | Journal of the Western Society of Engineers; Volume 8 |
Railroad History Citation | ICC Valuation Information, Compiled by Richard S. Steele |