Dubuque Railroad Bridge

Located between Dubuque, Iowa and East Dubuque, Illinois; this large through truss swing bridge carries the former Illinois Central Railroad across the Mississippi River. The present bridge is the second bridge constructed at this location. The first bridge at this location was authorized by Congress in 1866. The Dunleith & Dubuque Bridge Company was formed in 1867 to connect the Illinois Central Railroad at Dunleith, Illinois (now East Dubuque) with the Dubuque & Sioux City Railroad at Dubuque. The company quickly came under control of the Illinois Central Railroad, which funded the construction of the bridge. A bridge at Dubuque was critical to the Illinois Central, as it would link the developing railroad network west of the Mississippi River with Chicago. Due to the nature of the Mississippi River at this location, a high level bridge would not be feasible, and a drawbridge would be required. During the design process, it was decided to use iron in the truss spans.

A contract was signed on January 14, 1868 with the Keystone Bridge Company for the construction of iron truss spans. Saulpaugh & Company was contracted the same day to construct the substructures. Colonel Rosewell B. Mason created general specifications for the bridge, and the spans of the new bridge would be designed by Jacob H. Linville. Construction on the bridge was ongoing throughout 1868, and was completed in December of that year. Initially, the bridge consisted of a 356-foot swing span, approached by a 250-foot span on the east side, and one 250-foot and four 225-foot spans on the west side. The trusses of the bridge utilized a Linville Variant Whipple through truss design, with pinned connections and Keystone columns. The substructures of the bridge were constructed of stone, quarried at an unknown location. Due to a large bluff along the east bank of the Mississippi River, a large tunnel would be constructed by Saulpaugh & Company, which allowed for the railroad to curve south.

Originally, the bridge was approached by a long wooden trestle on the west end of the bridge. This trestle was gradually filled, and in 1872; the same contractors were retained to construct an additional eight through truss spans over a swamp near present day Harbor Park. A revision of the plan resulted in only seven spans being constructed, with the eighth sold to the Chicago, Dubuque & Minnesota Railroad (later Milwaukee Road) for use across the Volga River in Clayton County, Iowa. The remaining seven spans consisted of 98-foot, 8-panel, pin-connected Pratt through trusses, which also utilized Keystone columns. The trestle between the sets of iron spans was gradually filled during the 1870s, eventually leaving the two structures separated. In November 1887, the western two spans of the approach bridge were filled, and the spans were sold to E.A. Spaulding, a local bridge builder. It is unknown what the final disposition of those spans is. In October 1889, the eastern two trusses of the approach bridge were sold to E.E. Firth, another local contractor. It is believed that Firth sold the spans to Dubuque County, which reused them for roadway bridges in the county. One of the trusses was used to carry Hempstead Road over White Water Creek west of Bernard, and has since been reused at Bergfeld Pond on the west side of Dubuque. The other span was reused to carry Clay Hill Road over the Little Maquoketa River near Durango, and has since been placed along the Heritage Trail. In 1892, the remainder of the approach bridge would be filled, and the remaining three spans sold to the Illinois Central Railroad. Two of the spans were reused at Vicksburg, Mississippi; and the disposition of the third span is unknown.

In 1892, Keystone Bridge Company was contracted to replace the swing span of the bridge. Starting in 1899, the remainder of the bridge was replaced by new through truss spans, fabricated by American Bridge Works. As the sloughs on the west side of the bridge had been drained and redeveloped, the bridge would be shortened by one 225-foot span on the west end. During the reconstruction of the bridge, the substructures of the bridge were extensively rebuilt. Concrete encasement was added to the piers and east abutment, and a new west abutment was constructed by modifying the stonework of the original pier. It is unknown if the substructure work was completed by contract or by railroad forces. Work on the bridge was completed in 1900, and was reportedly completed using ordinary methods. It is believed that the old iron truss spans were scrapped upon replacement, as the large sizes and lightweight nature of the spans made them impractical to reuse.

Currently, the bridge consists of a 356-foot, 14-panel, pin-connected Pratt through truss span, flanked by a 250-foot, 10-panel pin-connected Parker through truss span on either side. Three additional 225-foot, 9-panel spans of the same design approach the bridge on the west side. The swing span would use a typical design for the era, including lightweight built up members, an inclined top chord and a lattice portal. The span functions as a rim-bearing swing span, where the drum which holds the truss span is set onto a round roller nest, which turns the bridge. The approach spans use a typical design for Illinois Central truss spans, modified to allow for longer spans. These spans utilize lightweight laced vertical members, a tall sway bracing and a typical portal bracing found on American Bridge Works spans, consisting of four bays of X-bracing. Decorative heel bracings are also used on the bridge, typical of American Bridge Works spans. These spans appear to use a Parker design, to accommodate the longer length required. The original floor of all spans used a standard design, consisting of stringers made of plate girders, and floorbeams located at the panels.

Since the 1900 reconstruction, the bridge has seen relatively little change. The bridge received a significant rehabilitation between 2012 and 2013. This rehabilitation included the strengthening of tension members of the bridge with new steel, rebuilding the existing connections with new plates and bolts, and adding additional steel repairs throughout the bridge. While these repairs greatly altered the appearance of the spans, all of the original material appears to have been retained. Overall, the bridge appears to be in fair condition, with no significant deterioration noted. The author has ranked this bridge as being highly significant, due to the unique combination of truss spans, as well as the history of this bridge. Recent repairs to the bridge likely indicate that this bridge will remain in service for years to come, and these repairs do not detract from the significance of the structure.