Government (Arsenal) Bridge

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Located between Davenport and Arsenal Island, this iconic through truss swing bridge carries the former Chicago, Rock Island & Pacific Railway and Fort Armstrong Road across the Mississippi River. In the early 1850s, railroads were rapidly extending west from Chicago, and a transcontinental railroad was being planned. The largest barrier for railroads looking to extend west from Illinois was the Mississippi River, which was heavily used by river traffic. The Illinois Legislature approved plans for a bridge across the Mississippi River in 1853. The railroad planned to cross Sylvan Slough on a wooden bridge and run across Arsenal Island, before crossing the Mississippi River on a large bridge. Construction began on the bridge in 1854, and it was completed in early 1856.

The first bridge consisted of a wooden Howe through truss span, set onto timber pile substructures. The main span of the bridge consisted of a 286-foot swing span, which was balanced on a center pivot pier. The swing span was approached by two 250-foot spans on the east side, and three 250-foot spans on the west side. The fixed spans of the bridge were reinforced with timber arches, which were seated on notches constructed in the piers. Only two weeks after opening, the bridge was struck by the steamboat Effie Afton, which caused the collapse and burning of one bridge span. As river traffic had been unimpeded for years prior to the construction of this bridge, the bridge became controversial. Steamboat interests alleged that the swing bridge was an impediment to navigation, while the railroad desired to maintain the bridge. Abraham Lincoln, a young lawyer from Illinois, was retained by the railroad to defend the structure. After a series of court cases ended in a hung jury, the bridge was allowed to remain. These court cases would be fundamental in the development of additional railroad bridges across the Mississippi River.

Between 1856 and 1859, the wooden piers of the bridge were replaced by new stone piers. By the late 1850s, the original bridge had become deteriorated and too light for traffic. Tension cables were added in the late 1850s or early 1860s to strengthen the wooden trusses. In 1866, the first bridge would be replaced by a new wooden McCallum through truss bridge, reusing the piers. Despite the new bridge, steamboat companies continued to fight for the removal of this bridge, citing a large amount of wrecks caused by the bridge. The stone piers of the bridge were not positioned well, and were not placed parallel with the flow of the river. During the mid-1860s, the United States Army, which operated an arsenal on Rock Island (now Arsenal Island) considered the railroad to be a nuisance. A new bridge approximately 1/2 mile downstream was authorized in 1866, and work on the new structure began in 1868. In 1868, the bridge was severely damaged when an ice flow knocked a stone pier out of alignment, and later when a tornado destroyed a span of the bridge. Temporary repairs were made to the structure as the new bridge was constructed.

Unlike previous bridges, the new structure would be constructed of wrought iron and steel. In addition, the bridge would be constructed with two decks, permitting the passage of railroad traffic on the upper deck and wagons and pedestrians on the lower deck. The new bridge would be located downstream, and the railroad realigned to avoid cutting across the middle of the island. As the new bridge also provided a crucial connection to Arsenal Island, the United States Government jointly funded and led the project. Initially, the bridge project was led by the Ordinance Department, but was placed under the direction of Major G.K. Warren in 1869 and Col. Macomb in 1870. C. Shaler Smith was named the Chief Engineer for the project. A contract was awarded to the Baltimore Bridge Company for the superstructure, and an additional contract was awarded to an unknown contractor for the construction of new bridge piers. However, the substructure contractor was ineffective, and the United States Government finished the project using hired labor. After the completion of the third bridge in 1872, the old bridge was removed, and only the east abutment remained. The new bridge would run across the river at a north to south bearing.

The third bridge utilized a 366-foot centerbalanced swing span, which was located near the Illinois shore. Approaching the swing span on the north included a 258-foot span, three 216-foot spans and another 258-foot span. To carry the railroad over the roadway approaches, a 99-foot through truss was installed for the railroad deck east of the swing span, and a 197-foot span was installed on the west end. The main spans of the bridge utilized a variation of the Whipple through truss design, and utilized pinned connections and Phoenix Columns. The approach spans each used a pin-connected Pratt through truss span. Stone for the piers would consist of limestone, quarried near Joliet, Illinois. After nearly 20 years of use, the bridge had become too light for traffic. In 1891, the original wooden floor system was replaced by iron. Throughout the early 1890s, proposals were made to replace the outdated third bridge. The Rock Island had completed a second track between Chicago and Rock Island in the late 1880s, greatly increasing traffic over the bridge. A new superstructure was authorized by Congress in 1894, and $490,000 was awarded to fund the construction of the new bridge.

In 1894, Ralph Modjeski was retained to design a replacement bridge, which would carry two tracks on an upper deck and two roadway lanes on the lower deck. In addition, streetcar tracks were planned for the lower deck. To construct the new bridge, the use of falsework was permitted to construct the new superstructures. However, erection of the swing span was required to be completed between November and March to avoid interruption to river navigation. As part of the project, the railroad would need to be raised approximately 2 feet without interrupting railroad traffic. It was determined that the most economical solution was to modify the existing piers with new stone, and construct a new superstructure with spans of the same dimensions. Contracts were awarded to Phoenix Bridge Company for the fabrication and erection of the new superstructure, and to Sooysmith & Company for the modifications to the piers.

Preliminary work was completed on the bridge in the fall of 1895. As soon as navigation closed in November of that year, falsework was erected across the navigation channel. However, delays in the fabrication of the span required the old swing span to remain in place until the new span was ready to be erected. In late December 1895, work on removing the old swing span began, which was completed in January 1896. Throughout February, the new swing span would be erected. Typical of bridge projects in this era, the trusses would be erected by use of a traveler, which was supported by the falsework. A sudden cold snap caused a significant build up of ice on the river, and a quick warm-up led to a large ice flow endangering the work. At this time, the swing span was only partially complete, and the falsework and traveler were in immediate danger. On February 25, the construction site could take no more ice, and the partially completed swing span, traveler and falsework were crumpled by the ice. Five days later, the falsework was repaired and railroad traffic resumed using the old bridge. New members were ordered, and work on the swing span was halted.

As March rapidly approached and river navigation resumed, it became apparent that a temporary solution was needed to maintain river traffic. The solution devised included reusing a combination through truss span, provided by the Rock Island Railway, as a lift span. Simple towers and counterweights were constructed, and the temporary span was powered by electricity. The innovative solution required less than one minute to raise or lower, and was operated several times per day between March 26 and early May, when the new swing span was completed. As work resumed on the swing span, it was found that the drum and tower sustained minimal damage, and could be repaired for use. On May 25, the new swing span was swung into place. The temporary lift span was removed by demolishing the towers and lowering the span onto a barge, after which it was scrapped. After completion of the swing span, the remaining spans were erected with little difficulty, and the bridge was fully completed by the end of 1896. Iron from the old bridge was reportedly offered for sale, although it is unknown if it was used anywhere or simply recycled.

Since the 1896 reconstruction, there have been a number of alterations to this bridge. The railroad ties on the upper deck were replaced in 1908, and the roadway deck was replaced by a new creosote deck in 1909. At this time, the Tri-City Railway Company replaced the streetcar tracks on the lower deck with new tracks. In conjunction with the proposed construction of a lock and dam at the bridge, the original stone piers were mostly encased in concrete between 1923 and 1924. In 1929, the Rock Island contracted with Strobel Steel Construction Company to fabricate new floor beams, stringers and a metal deck for the railroad deck. Between 1931 and 1933, the center pier of the bridge was reconstructed as part of the Lock and Dam #15 project. The pier would be incorporated into the guide walls of the two locks, and was set between two parallel locks. Further alterations were made in 1957, when connecting pins were replaced in the superstructure, members were repaired, and a new concrete deck was installed on the lower deck. The western roadway approach was reconstructed in 1960, and a steel stringer span on a new concrete abutment added. Recent repairs include the strengthening of the bridge for modern traffic.

Currently, the bridge consists of a 366-foot, 16-panel, pin-connected Baltimore through truss swing span (span G). This swing span consists of two halves, which are connected by a tower over a center pivot pier (pier #7). On the north end, the bridge is approached by five double deck through truss spans, and a smaller through truss span carrying the railroad deck only. The northern span, span A, consists of a 197-foot, 9-panel, pin-connected Pratt through truss span. This span utilizes a lattice portal bracing, built up vertical members and eyebars for the lower chord and tension members. Spans B and F consist of 258-foot, 12-panel, pin-connected Baltimore through truss spans, and spans C, D and E use a 216-foot, 10-panel version of the same design. On the south end, the bridge is approached by a single 99-foot, 5-panel, pin-connected Pratt through truss span (span H), which carries the railroad deck. This span utilizes similar members to span A, but uses a solid bar for portal bracing. The Baltimore through truss spans all utilize heavily built-up vertical members, eyebars for the tension members and a large X-frame portal bracing.

The floor of the roadway and railroad decks is traditionally composed, consisting of girders for the stringers, which are connected to the floor beams. The roadway deck utilizes an open metal grate, which is not original to the structure. In addition, the cantilevered sidewalks use decorative handrails, adding to the attractiveness of this bridge. The railroad deck utilizes a sheet metal ballast deck, which forms a trough. The northern roadway span utilizes a flared steel stringer, which follows a standard design for bridges in Iowa. All substructures of the bridge consist of stone, except for the roadway north abutment. These substructures are constructed of Joliet limestone, and were extended by sandstone quarried at Sandstone, Minnesota and limestone from Anamosa, Iowa. Electrical towers were installed on the top of the bridge, which serve the swing span.

Through truss bridges were popular for large bridges, as they provided a durable structure while minimizing the number of mid-river piers. Pratt through trusses were the standard for much of the late 19th Century, as the design was simple, durable and easy to construct. The approach spans both utilize a later variation of this design, with heavier members, larger pins and heavier portal and sway bracing. The Baltimore through truss design became popular in the 1890s, as an alternative to Whipple trusses. While Whipple through trusses were the standard for iron Mississippi River crossings, Whipple trusses were mathematically complex and did not produce a statically determinant result. As a result, the design grew out of favor for railroad use around 1890 and alternatives were introduced. The Baltimore through truss was a modification of the Pratt through truss design, which adds sub panels and middle connections. This type of span is particularly well suited for a double deck design, as the taller trusses required allowed for plenty of room for a second level.

The swing span utilizes a rim bearing design, where the truss span sits on a metal drum, which turns on a set of wheels known as the roller nest. A machinery house is located on the swing span, which is a basic finished office with the required machinery. The swing span is operated by an electric motor, and can turn a full 360-degrees, unusual for a swing span. Swing spans typically have two required movements to rotate, including the locking/unlocking of the ends, and the actual turning about the center pier. On this bridge, the locking mechanisms are first disengaged, and the bridge lowered to allow for clearance to rotate. Power is then added to the bridge, which allows the span to rotate. Reportedly, the bridge is most often operated by wind power, which is controlled by using the brake. On any given day, the swing span opens and closes several times, which allows river traffic to use the dual locks located under the bridge.

Despite a large number of alterations, this bridge retains a high level of historic significance. In addition to this crossing contributing to the growth of railroad travel in the United States and providing the first bridge across the Mississippi River, this bridge represents an early use of the Baltimore through truss design. In addition, relatively few double deck bridges such as this remain in use in the United States, particularly with a roadway lower deck and a railroad upper deck. Overall, the bridge appears to be in fair condition, and is well maintained. The State of Iowa reportedly desires to replace this bridge at some point, leaving its future uncertain. However, other sources report that the bridge has only used a small percentage of its service life. The author has ranked this bridge as being nationally significant, due to the design, age and history of this crossing.