Click the photo to view the full-size version
| Name | CN Thornapple River Bridge |
| Built By | Wisconsin Central Railway |
| Currently Owned By | Canadian National Railway |
| Superstructure Contractor (Truss Span) | Wisconsin Bridge & Iron Company of North Milwaukee, Wisconsin |
| Substructure and Approach Contractor | Unknown |
| Length | 240 Feet Total, 125 Foot Main Span |
| Width | 1 Track |
| Height Above Ground | 20 Feet (Estimated) |
| Superstructure Design | Pratt Through Truss and Concrete Arch |
| Substructure Design | Concrete |
| Date Built | 1907 |
| Traffic Count | 15 Trains/Day (Estimated) |
| Current Status | In Use |
| Canadian National Railway Bridge Number | 357.50 |
| Significance | Moderate Significance |
| Documentation Date | 5/6/2016 |
In 1906, the Owen and Northern Railway Company (O&N) had begun constructing a 45 mile railroad line, extending from the existing Wisconsin Central Railway (WC) mainline at Owen, Wisconsin to Ladysmith, Wisconsin. At the same time, the WC acquired the partially completed property of the O&N, and completed construction as part of a bigger project to construct a new line to reach Lake Superior at the Twin Ports. Between 1906 and 1909, the WC constructed 112 miles of new railroad, extending from Ladysmith, Wisconsin to Superior, Wisconsin and Duluth, Minnesota. In 1909, the WC would be leased by the Minneapolis, St. Paul & Sault Ste. Marie Railway (Soo Line), which itself was controlled by the Canadian Pacific Railway (CP). In 1910, an additional 19 miles were constructed between Spencer, Wisconsin and Owen, Wisconsin. These projects were among several major projects undertaken by the WC/Soo Line, which included constructing new lines and revising existing lines to improve operations. This line would serve as a principal mainline for the WC/Soo Line, connecting the Chicago with the Twin Ports while bypassing the Twin Cities.
The Soo Line had constructed and acquired a large network of railroads, connecting the Upper Midwest with Canadian Railroads. Throughout the early 20th Century, this line remained a critical mainline for the Soo Line, which owned sprawling terminal facilities in Duluth and Superior. In addition, the line connected to additional secondary lines which extended into central Minnesota from Duluth. In 1961, the WC would be merged with other CP subsidiaries Duluth, South Shore & Atlantic Railroad and the Soo Line to form Soo Line Railroad, a company controlled by CP. In 1984, the Soo Line would be reorganized as the Soo Line Corporation in advance of a pending purchase of the Chicago, Milwaukee, St. Paul & Pacific Railroad (Milwaukee Road).
In 1987, this line would be sold to Wisconsin Central, Ltd. (WC). Known as the "new" Wisconsin Central, the railroad acquired several excess rail lines from the Soo Line, Milwaukee Road and Chicago & North Western Railway. In 1988, a portion of the line between Gordon, Wisconsin and Ambridge, Wisconsin was abandoned in favor of the parallel Chicago & North Western Railway route, which had also been acquired by the WC. The former Soo Line route would be purchased for trail use. In 2001, WC was merged into Canadian National Railway (CN), becoming the American subsidiary of CN. Today, CN continues to operate the Spencer to Superior segment as the northern portion of the Superior Subdivision, which provides the main CN access to the Twin Ports from Wisconsin. The Wild Rivers Trail currently uses the former Soo Line route between Gordon and Ambridge.
Located in rural Rusk County northwest of Ladysmith, this small through truss bridge carries the former Soo Line over the Thornapple River. This bridge was constructed in 1907, when the Wisconsin Central was constructing a new line between Owen and Duluth. The bridge consists of a 125-foot, 4-panel, riveted Pratt through truss span, set onto concrete piers. The south approach consists of a single 37-foot concrete arch span, while the north approach consists of three 23-foot concrete arch spans. The truss was fabricated by the Wisconsin Bridge & Iron Company, while the approaches and substructures were constructed by an unknown contractor. The truss span was heavily modified in approximately 2006 to accomodate taller and heavier trains, giving the structure its current configuration.
As originally constructed, the truss span used a somewhat unique design, with unusual members composed of built-up beams constructed using both V-lacing and square plates. Similar spans nearby originally used a deep lattice portal bracing, which was likely present on this bridge. Since the initial construction, the truss span has been heavily modified, including replacing the stringers, floorbeams, some diagonal members, the upper and lower lateral bracing, the portal bracing and some rivets with high strength bolts. New material appears to be a high strength steel, which is an orange color. In addition, the original endposts, upper chords and lower chords were strengthened with additional plates. These alterations have severely impacted the historical integrity of the span, although the repairs were critical for the continued use of the bridge. The replacement of the portal bracing was likely needed to allow for double stack intermodal trains to use the bridge. Riveted Pratt trusses are somewhat unusual. Most Pratt truss spans were constructed using pinned connections instead of riveted connections. Overall, the bridge appears to be in good condition, and continues to serve a well-used railroad line. The author has ranked this bridge as being moderately significant, due to the truss design and extensive modifications.
Citations
| Builder and build date | Wisconsin Bridge & Iron Company plaque |
| Railroad History Citation | ICC Valuation Information, Compiled by Richard S. Steele |