Iron Belle Trail - 1st Avenue Bridge

Located in Bessemer, this unusual pony truss/girder hybrid bridge carries the former Soo Line Bessemer Branch over 1st Avenue. It is unknown if there was a previous bridge at this location. During the 1890s, the Wisconsin Central Railway invested significant capital into this line, replacing aging wooden bridges with stronger steel structures. The present bridge at this location was constructed in 1896. Currently, the bridge consists of an unusual 105-foot, 7-panel, riveted double intersection Warren pony truss/through plate girder hybrid span, approached by timber pile trestle spans on either end. The entire bridge is set onto timber pile substructures, and the structure is located on a curve. Typical of WC bridges from this era , the main span was fabricated by Wisconsin Bridge & Iron Company. Railroad company forces constructed the approaches and substructures, as well as erected the steel span. It is unknown if the span was designed by a railroad company engineer or by an engineer with the Wisconsin Bridge & Iron Company.

It appears that the span across 1st Avenue was an experimental design, and no similar spans are known throughout the WC system. The main span uses a polygonal top chord, light members and a traditionally composed floor. The top and bottom chords are comprised of light steel channels, as are the endposts. The diagonal members are composed nearly exclusively of light beams, and the vertical members are composed of triangular beams with V-lacing connecting the channels. Unique to this bridge, the ends of the span are comprised of plate girders, the ends of which are only approximately 4 feet tall. The floor uses a typical design, with plate girder floorbeams, light I-beam stringers and X-laced members for the end floorbeams. The unusual configuration of the main span gives the bridge a trapezoidal shape. While commonly seen on 1880s truss spans, the thin gusset plates are very unusual for a span of this age. Since the initial construction, there have been no significant alterations to the main span. In 2016, the bridge was repaired for trail use. As part of the repairs, the stringers of the approach spans replaced and a wooden deck and railings added to the bridge. Currently, the bridge is used by the Iron Belle Trail, and has been listed on the National Register of Historic Places. Overall, the bridge appears to be in fair to good condition, with no significant deterioration noted. The author has ranked this bridge as being highly significant, due to the unusual design. In addition, the bridge is one of only two known grade separations in Michigan to use a truss design.