Clinton Railroad Bridge (Main Channel)

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Located immediately south of the Gateway Bridge, this large through truss carries the former Chicago & North Western Railway over the main (west) channel of the Mississippi River at Clinton. In the 1850s, the Galena & Chicago Union Railroad constructed a line heading west from Chicago, reaching the Mississippi River at Fulton in 1855. In 1859, the Cedar Rapids and Missouri River Railroad was charted to construct a new railroad line across Iowa, connecting the Mississippi River at Clinton to the Missouri River at Council Bluffs. At Clinton, the Mississippi River is divided by Little Rock Island, dividing the river into two channels. While the Iowa side of the river is set onto solid ground, the Illinois side of the river consists of a large slough. In 1859, a short extension would be made to a point across the Mississippi River from Clinton, and a wooden bridge would be constructed across the slough and eastern channel. A car ferry was established to connect to Clinton, with the intention of constructing a permanent bridge within a few years. Work on the permanent bridge would begin in 1864, and the bridge would be completed in 1865. The main (west) channel bridge would utilize a swing span to allow river traffic to pass. In the late 19th Century, traffic on the line grew, and the crossing would be upgraded at various times.

The first bridge across the main channel was completed in 1865, and consisted of a 300-foot Bollman through truss span, approached by a 200-foot and a 175-foot wooden Howe through truss on the east side and a 175-foot span on the west side. The swing span consisted of two equal 150-foot Bollman trusses, joined at a tower and connected by chains. The substructures of this bridge were constructed of stone, except for the swing pier, which was constructed of timber cribbing filled with rock. The bridge was first reconstructed in 1874, when the Howe trusses were replaced by pin-connected Whipple through trusses of the same design, which were fabricated by the American Bridge Company of Chicago. In 1887, the swing span was replaced by a pin-connected Pratt through truss span, which was balanced on a new stone pier. This span used heavier built up members, a lattice portal and seven panels per half. In 1898, the Whipple through trusses were replaced by new pin-connected Pratt through truss spans, fabricated by the Detroit Bridge & Iron Works.

By 1900, the entire line between Chicago and Council Bluffs had been double tracked, with the exception of this bridge. Recognizing the importance of this crossing, C&NW leadership began to explore ways to improve the crossing and operations in Clinton. Surveys were made for the new structure in 1901, and by 1907, plans had been approved by the War Department and by railroad leadership to replace the bridge. Due to the topographical constraints of the location, the new crossing would be required to be constructed on roughly the same elevation, and would require a swing span over the main channel. The new crossing would be constructed immediately downstream of the old bridge. As part of the work, a large amount of timber trestle on the Illinois side would be filled, and the crossing would be constructed of three separate bridges. In addition, a new cutoff bypassing Fulton was constructed to improve grades approaching the crossing on the Illinois side.

A contract for the substructures of all three structures was awarded to the Foundation Company on May 18, 1907. This was followed by a contract for the superstructure of the slough and east channel bridges to the Wisconsin Bridge & Iron Company on May 21, 1907. A final contract was awarded to the Pennsylvania Steel Company for the superstructure of the main channel bridge on February 3, 1908. This company elected to subcontract the erection work to the Missouri Valley Bridge & Iron Company. The new structures were designed under the direction of Edward C. Carter, Chief Engineer; William H. Finley, Assistant Chief Engineer; and I.F. Stern, Engineer of Bridges. Work on the substructures was began in January 1908, and was completed by November of that year. Erection of the superstructure was started in December 1908, and was completed by early 1909. Traffic was switched to this bridge in the spring of 1909, and the old bridge was removed soon after. Portions of the old bridge were reused on branch lines throughout the system, including at Oral, South Dakota; Whitewood, South Dakota; and Niagara, Wisconsin.

Currently, the bridge consists of a 462-foot swing span, which is approached by a 150-foot riveted quadrangular lattice through truss and a 186-foot, 7-panel, riveted Parker through truss on the east and a 55-foot deck plate girder span on the west. The swing span is comprised of two 231-foot halves, which are joined over a center pier by a tower. These halves both contain 8 panels, contain both pinned and riveted connections, and use variants of two different truss designs. The entire bridge is set onto stone substructures, which were constructed of Ablesmans Sandstone, quarried at Rock Springs, Wisconsin. Stone for the abutments was quarried at the "red rock" quarry, and stone for the remaining piers was quarried at the "white rock quarry" The piers for the bridge were constructed using caissons, which were sunk to solid limestone bedrock. Both stones were among the highest quality stone that could be sourced in the Midwest.

Typical of swing spans constructed during this era, the span uses a rim bearing design, and does not follow any specific truss pattern. A large tower connects the two halves of the swing span, and consists of a pair of heavily constructed A-frames, connected by bars and built up members. This span is extremely heavy for a swing span, and is believed to have been the largest swing span constructed when it was completed. Similar span sizes were used as the previous bridge to avoid disturbing the old piers during construction. This configuration required a slightly larger truss span immediately east of the swing span. A Parker through truss was likely chosen, as the span was longer than typically constructed for lattice trusses. All truss spans use a standard floor, consisting of stringers constructed of girders. Portal bracing on all truss spans consists of an M-frame design, and these spans all use heavily constructed members.

Rim-bearing swing spans became the standard swing span design by the 20th Century. These types of swing spans function by turning on a roller nest, which contains wheels on a track. Set on the roller nest is a steel drum, to which the main truss span attached. The swing mechanism is turned by electric motors, and was the first such bridge across the Mississippi River to use an electric motor. It appears that much of the original turning mechanism remains intact. The outer ends of the trusses consist of riveted a Warren pattern, while panels closer to the center tower consist of a variant of the pin-connected Pennsylvania design. The use of hybrid truss designs was required due to the complex geometry of the span. Members of the truss use a combination of built up beams and eyebars, typical for pin connected spans from this era. A bronze Chicago & North Western Railway logo, which was originally installed above the portal of the swing span, was removed some time ago.

Although the lattice truss design was popular in Europe, few American railroads utilized the design. While Union Pacific Railroad, the Chicago, Rock Island & Pacific Railway and a handful of eastern railroads utilized the design to various extents, no railroad constructed as many lattice truss bridges as the C&NW. Between 1878 and 1930, through trusses constructed by the C&NW nearly exclusively used this design. Although lattice trusses were not popular with American railroads after the 1880s, the C&NW relied heavily on this design, as it had proven to be resilient towards derailments and damage. The main drawback of the design was the unpredictable nature, as the structure was not statically determinant. These types of spans were typically used for lengths less than 175 feet. The lattice span of this bridge uses a combination of built up and solid members, typical for bridges of this design. The Parker span utilizes mainly built up members, giving the span a heavy appearance.

Since the initial construction of the bridge, the structure has seen a few changes. Strengthening and various repairs have been made to all spans, to increase loading capacity and fix damage. As of 2025, plans are underway to replace this bridge with a new high level crossing immediately south of the structure. This new crossing will improve river navigation, and minimize delays to railroad traffic. No definite timeline for construction has been released. It is expected that this bridge will be demolished after the new bridge is complete. Overall, the bridge appears to be in fair condition, with some deterioration noted throughout the bridge. The author has ranked this bridge as being highly significant, due to the design and history of this crossing.