Bismarck Railroad Bridge

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Located across the Missouri River between Bismarck and Mandan, this large railroad bridge is an iconic piece of North Dakota history. As the Northern Pacific sought to expand westwards towards the West Coast, George S. Morison was retained to design and construct a bridge across the Missouri River. Morison had recently completed a large bridge across the Missouri River at Plattsmouth, Nebraska. Two options were proposed for the bridge at Bismarck: one option would involve two 500-foot spans, while a second option involved three 400-foot spans. Construction on the first bridge at this location began in late 1880, but would be halted due to flooding in 1881. Excavation for the bridge piers was begun in May 1881, and construction on the piers themselves began in October 1881. Stone for lower portions of piers #1, #2 and #4 was quarried at Watab Quarry near Sauk Rapids, Minnesota; and the remainder of the stonework was quarried at Rock Island Qaurry; also near Sauk Rapids. Work on the piers was completed in June 1882, and work on the trusses was completed in October 1882. The trusses consisted of three 400-foot pin connected Whipple through truss spans, approached by a 115-foot deck truss span on the west end and a 140-foot span on the east end. The iron for the bridge was fabricated by the Detroit Bridge & Iron Works.

By 1905, the original bridge had become too light for traffic. In response, Northern Pacific sought to replace the structure, and Ralph Modjeski was hired to design a new bridge. The new bridge featured three 400-foot 14-panel pin connected Pennsylvania through truss spans, set onto the original stone piers. A 115-foot 12-panel riveted Warren deck truss was constructed on the west end of the bridge, and a 140-foot 6 panel Pratt deck truss would be constructed on the east end. The deck truss spans utilized a Lattice girder design, which is essentially a thin deck truss. The western deck truss would be only 10 feet deep. The bridge was fabricated by American Bridge Company at the Ambridge Plant, and was placed into service in 1906. Due to the mainline status of this rail line, minimal traffic interruptions were allowed during the replacement process.

Since the initial construction of the bridge in 1882, severe shifting has been documented at the east end. Erosion and shifting in the hillside caused the east pier to move by three inches per year. In May 1898, the pier would be excavated, placed onto rollers and shifted back into the proper location. The pier shifted four more inches between 1898 and 1902; and a tunnel would be constructed near the east pier to help slow the shifting. Issues with the east pier continued, and the pier moved an additional 12 inches in 1917 alone. By 1947, movement had reached unsafe levels, and the issue was further investigated. It was decided to excavate additional areas on the eastern hill, and add a beam span in 1950. Since this repair, shifting has slowed significantly.

The bridge has seen additional improvements since 1950. A 30-foot steel stringer span was added to the east end of the bridge in 1980, and the west approach would be reconstructed with modular concrete girders and steel pile piers in 1991. Despite these changes, this bridge retains strong historical integrity, and is likely the most iconic railroad bridge in North Dakota. However, BNSF is currently working on a replacement bridge upstream of this bridge. Current plans are to remove this bridge once the new bridge is complete. Groups are currently in court to save the bridge, and convert it to a pedestrian bridge; while BNSF strongly opposes this idea. Overall, the bridge appears to be in fair condition, but is reaching the end of its functional life as a railroad bridge. The author has ranked this bridge as being highly significant, due to the unique and large scale design.