Soo Line S-Bridge

Located near Galloway Street in Eau Claire, this unique deck truss bridge carries the former Soo Line across the Eau Claire River. When the Wisconsin Central Railway (WC) first attempted to extend south of the Eau Claire River, geometry posed a serious problem. The railroad entered Eau Claire along the north bank of the river, and did not have enough room to get a sweeping curve to cross the river at an acceptable angle. Instead, it was decided to build an S-shaped bridge with sharp curves to alleviate this issue. The first bridge at this location was constructed in the fall of 1890, and consisted of five wooden deck truss spans. This bridge was constructed by Shailer & Schniglau of Chicago, and sat on timber pile substructures. By the early 20th Century, this bridge had become too light for traffic, and a replacement was needed. In addition, the Minneapolis, St. Paul & Sault Ste. Marie Railway, which began leasing the WC, sought to upgrade existing facilities, replacing substandard bridges with new steel and concrete structures. Construction on a new bridge began in the spring of 1910, and work progressed through 1910, until the old bridge was demolished and the present bridge opened on October 1st, 1910.

Currently, the bridge consists of three 100-foot, 11-panel, riveted Warren deck truss spans, approached by a 70-foot deck plate girder span on either end. The entire bridge is set onto concrete, and runs at an S-shape, with two sharp curves near either end. Because of the curved shape, the trusses use an unusual skewed geometry, are slightly offset from each other and also overlap slightly. The truss spans are heavily constructed, using mainly built-up members. The top chord, bottom chord, vertical members and diagonals are all constructed using heavily laced beams, which use an X-lacing. The connections of the truss are heavily constructed, using a typical riveted design. To accommodate the unusual skew, the spans use an 11-panel design, with the expected eastern panel and diagonal member omitted. The deck plate girder spans use a standard design, and are constructed to accommodate the shape of the bridge. Piers for the bridge use a typical square shape with a pointed ice breaker on the upstream face, and are likely founded on timber piles. The east abutment uses an elongated parapet design, while the west abutment uses a more traditional design with wing walls. Minneapolis Steel & Machinery Company fabricated the superstructure, while masonry crews employed by the Soo Line constructed the substructures. Erection of the new bridge was handled by Frankman Brothers Construction Company.

This design of truss span was preferred by the Soo Line, as it was durable and easy to construct. Warren trusses became popular during the early 20th Century, as they provided greater strength and rigidity than their pin-connected counterparts. Deck plate girder spans were also often used by railroads, as they are durable and easy to construct. The use of company forces to construct concrete substructures was common for the Soo Line, which found the practice more economical than hiring a contractor. Minneapolis Steel & Machinery Company was known to have constructed a number of similar deck trusses, as well as other spans, for the Soo Line. Overall, the bridge appears to be in good condition, with minimal spalling or cracking noted to the substructures and little serious deterioration noted within the superstructure. Since being abandoned in 1991, the bridge has been reused as a pedestrian bridge and has become a local landmark, due to the unique shape. This unusual bridge was listed on the Wisconsin State Register of Historic Places in 2021 and on the National Register of Historic Places in 2022. The author has ranked this bridge as being regionally significant, due to the unique shape and truss design.