CPKC Black River Bridge

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Located in La Crosse, this bascule bridge carries the former Chicago, Milwaukee, St. Paul & Pacific Railroad (Milwaukee Road) mainline over the Black River as part of a series of four bridges crossing the Mississippi River. At this location, the Black River flows into the Mississippi River, and the two rivers are separated by a series of swamps, islands and back channels. A bridge was first authorized at this location in 1868, but was not immediately built. The act was renewed in 1872, and allowed for the Milwaukee & St. Paul Railway to construct a bridge at any point between La Crosse and Houston County, Minnesota. In 1875, the location was finalized, and construction on a crossing began. The first bridge was completed in December 1876, and consisted of one long structure with sections of iron spans over the Black River, east channel and main channel. The original structure across the Black River consisted of a 310-foot swing span, approached by timber pile trestle on either end. This first swing span was constructed of iron, and used wooden floorbeams. The swing span rested on a stone center pier, while the remaining substructures were constructed of timber piles. American Bridge Company (of Chicago) constructed the original superstructure, while an unknown contractor constructed the stone pier.

By the turn of the 20th Century, the original structure had become too light for traffic, and a replacement was planned. Work on a new series of bridges began in 1901, and was completed in 1902. The bridge was reconstructed with a new 308-foot, 12-panel, pin-connected Pratt through truss swing span. On the east end, the original trestle approach was replaced with two 65-foot and two 64-foot deck plate girder spans; and the west approach was replaced with two 65-foot foot and three 64-foot deck plate girder spans. The swing span was set onto new stone piers, while the approaches were set onto concrete piers. American Bridge Company (of New York) fabricated the swing span, while the approaches were fabricated by the McClintic-Marshall Construction Company. Typical of Milwaukee Road truss spans from this era, the swing span used heavily constructed members and a standard floor. The bottom and top chords were composed of built-up members, with heavy X-lacing. The endposts were also traditionally composed, with the front sides covered by plates, and the back sides connected by X-lacing. The vertical members were composed of tightly built-up beams, constructed using V-lacing. The diagonal members were all composed of steel bars, typical for bridges from this era. Also typical for this era of truss bridge, the portal and sway bracings both used a modified lattice design, with the portals using a solid curved heel bracing. Also typical of bridges from this era, the girders were composed of heavy plate girders with an open deck. The swing span was a rim bearing design, where the superstructure is rotated about a metal drum, set onto a track and turned by gears.

After over 100 years of serving heavy mainline traffic, the original bridge would be partially replaced in 2004. Much of the center of the bridge would be replaced with new spans, altering the configuration of the structure. As part of the work, the swing span and west three deck girders of the east approach were replaced to realign the navigation channel. A new bascule lift span was installed, and additional through and deck girders placed, giving the bridge its present configuration. Currently, the bridge consists of a 65-foot deck plate girder, followed by a 55-foot and a 50-foot deck plate girder span. The main span of the bridge consists of a 185-foot, 6-panel, bolted Warren through truss bascule lift span. The main span is approached on the west by a 108-foot and a 102-foot through plate girder, a 65-foot deck plate girder, three 64-foot deck plate girders and another 65-foot deck plate girder. All substructures of the bridge are constructed of concrete, and the newer piers use large concrete cassissons surrounded by sheet metal. The lift span uses a modern take on a single leaf rolling lift design, where the east end rolls on a track to raise the span. This type of lift span became popular in the 20th Century, as it was a relatively simple design. McClintic-Marshall Construction Company fabricated the original 64-foot and 65-foot girders in 1902, while Edward Kraemer & Sons constructed the 2004 spans. The original 1901-1902 concrete piers were constructed by Milwaukee Road company forces, which was typical for this railroad company.

The lift span is composed of solid steel members, with an M-frame portal bracing and large counterweights. A machinery house is located on the southeast side of the lift span, and an auxiliary machinery room is located near the counterweight. Bascule lift spans were popular for railroad lift bridges, as they were relatively simple and very versatile. Through and deck girder spans were also popular for railroad use, as they were durable and easy to construct. Despite the loss of the original swing span and some girders, the bridge fortunately retains the entire west approach in an unaltered state. Overall, the bridge appears to be in good condition, with no significant deterioration noted. The author has ranked the bridge as being locally significant, due to the lift design and retention of historic spans.