MPL Redwood River Bridge

Located near the station of North Redwood, this unique through truss bridge carries a former Minneapolis & St. Louis Railway branch line (now Minnesota Prairie Line) across the Redwood River. The first bridge at this location likely consisted of a timber truss bridge, constructed when the line was first built. In the late 1890s, the M&StL made several improvements to this line, replacing major bridges with steel and stone and replacing several smaller timber bridges with stone culverts. The present bridge was constructed in 1898. Originally, the bridge consisted of a much longer east timber pile trestle approach, which was filled and split into two separate structures in the early 20th Century. Currently, the bridge consists of a 121-foot, 6-panel, riveted Warren through truss span, approached by four timber pile trestle spans on the east end. The bridge is set onto a stone west abutment, timber pile pier and timber pile bents. In addition, the bridge runs at a heavy skew on account of the awkward angle the railroad crosses the river at. Phoenix Bridge Company fabricated the superstructure, while the Widell Company constructed the stone abutment. It is believed that the timber components were constructed by railroad company forces. Stone for the abutment consists of a tan granite, likely quarried near Morton, Minnesota.

The truss span follows an unusual design for the era, with heavy members, riveted connections and a standard floor system. Both the endposts and top chord use heavily built-up beams, which are composed of channels connected by X-lacing on the bottom and solid plates on the top. The bottom chord is unusual, as it is composed of four L-shaped bars connected by a single layer of V-lacing in the middle. The vertical truss members use a similar design to the bottom chord, and are constructed out of four L-shaped bars with V-lacing in the middle. The compression diagonal members are constructed out of solid beams, while the tension diagonal members use heavy X-laced beams. The floor system uses standard I-beam stringers and plate girder floorbeams, which are placed at the panel points. Both the upper and lower lateral bracing are composed of solid bars, which form an "X" shape across each panel. The portal bracing uses a thin double intersection lattice beam with diagonal bars for heel bracing. In addition, the sway bracing uses a similar design. The abutment uses a standard U-shaped design, with short walls extending parallel to the railroad. The timber pier is composed of square timber blocks, which are set onto sills.

Through the second half of the 19th Century, pin-connected Pratt truss spans were the most commonly used truss design for railroad bridges. In the mid-1890s, railroads began developing riveted truss designs, which provided a stronger and more rigid design. The Warren truss design became more widely used as riveted trusses were developed. As part of the 1898 work on this line, the M&StL ordered both an innovative riveted span that was installed here, as well as a traditional Pratt design that was installed at the Minnesota River nearby. The Warren truss design was economical, strong and simple. It is unclear why the M&StL used both riveted and pin connected spans as part of the same project. The Phoenix Bridge Company fabricated several truss spans for the M&StL in the late 1890s and early 1900s, with several spans using unique or experimental designs. Since the initial construction, the bridge has seen few alterations, except for the filling of much of the east approach. Today, a short timber trestle remains to cross an overflow of the Redwood River. Overall, the bridge appears to be in fair condition, with no significant deterioration seen on the truss. However, there is some deterioration on the timber components of this bridge that should be addressed to keep this bridge functional. It is likely that this bridge will be rehabilitated or repaired as funds become available. The author has ranked this bridge as being regionally significant, due to the unusual truss design.

Authors Note: Richard Sears was the station agent at North Redwood during the mid-1880s. He was selling watches from the depot, and later moved to Chicago to expand his business. Sears later joined Alvah R. Roebuck to form the Sears & Roebuck Company, which became a staple of American business. Read more here.