Hudson Swing Bridge

Located at Hudson, this swing bridge carries the Union Pacific Altoona Subdivision across the St. Croix River. The first bridge at this location was a wooden through truss bridge, constructed when the line was first built in 1871. The first bridge consisted of a 319-foot wooden Howe through truss swing span with a curved top chord, a 136-foot wooden Howe through truss span and a lengthy curved timber pile trestle approach. In 1881, the bridge would be replaced by a new iron bridge, set onto new stone substructures. To facilitate construction of the iron bridge, a temporary wooden shoe-fly bridge would be constructed, while the new bridge was constructed. The iron bridge consisted of a 319-foot, 24-panel, riveted quadrangular lattice through truss swing span, approached by a 156-foot riveted quadrangular lattice through truss and ten 84-foot, 7-panel, riveted double intersection Warren pony truss spans. The through truss spans used an arched and pedimented lattice portal bracing, typical of early quadrangular lattice through truss spans. The pony truss spans were lightly constructed, using a design typical for early 1880s pony truss spans. The superstructure was fabricated by the Leighton Bridge & Iron Works, while an unknown contractor constructed the stone substructures.

In 1898, the bridge would be upgraded by replacing the pony truss approaches with new Parker pony truss spans, fabricated by the Pencoyd Iron Works (also known as A&P Roberts Company). Spans from the old bridge were known to have been reused at Le Sueur, Minnesota and in Clark County, Wisconsin. The remaining through truss span and swing span would be replaced in 1913 by American Bridge Company. Nine of the ten pony truss spans were filled in 1922, and it is unknown if they were reused elsewhere. Based on the heavy construction, it seems unlikely that the spans would not have been reused for a branch line.

Currently, the bridge consists of a 319-foot swing span, consisting of two 6-panel riveted Pratt through truss spans, joined by a tower over the swing pier. The swing span is approached by a 156-foot 6-panel riveted Pratt through truss, and an 84-foot 6-panel Parker pony truss. The through trusses utilize A-frame portals, heavy built-up members and a traditionally composed floor. The pony truss span is also heavily constructed, using solid members and a traditionally composed floor. The bridge is set onto concrete piers, a concrete east abutment, and a stone west abutment. It is likely that the concrete was added to encase failing stone during the 1913 reconstruction. Pratt trusses were the most common type of railroad truss bridge during the late 19th Century, but were superseded by riveted Warren spans. It is somewhat unusual to see a riveted Pratt span, particularly by the 1910s. Parker pony truss spans were occasionally used, although many seem to have been constructed by the Pencoyd Iron Works for various railroads. These spans are noted for their curved top chord and heavily constructed members. This contractor is known to have fabricated dozens of examples, particularly for the Missouri-Kansas-Texas Railway. Overall, the bridge appears to be in fair condition, with no major deterioration noted. The concrete on the piers appears to be in failing condition, and will likely need to be addressed in the coming years. The bridge continues to rotate to allow boat traffic to pass. The author has ranked the bridge as being regionally significant, as it utilizes several different truss designs.