CN Escanaba River Bridge (Escanaba)

Authors note: This bridge has been included on this site to highlight a unique truss bridge which has since been replaced. Additional photographs and information about the bridge can be found at Historicbridges.org.

Once located in Escanaba, this unique through truss bridge carried the former Chicago & North Western Railway mainline over the Escanaba River and Escanaba & Lake Superior Railroad. The first bridge at this location likely consisted of a timber truss bridge, constructed when the line was first built. In 1875, the bridge was renewed with a new wooden Howe through truss bridge, believed to have been set onto timber substructures. The bridge was again rebuilt in 1882, with five 135-foot wooden Howe through truss spans, set onto stone substructures. This structure was built as part of an improvement project in the early 1890s, which saw the C&NW replace the significant river crossings across the Menominee River at Marinette, Wisconsin and across the Escanaba River at this location. By the late 19th Century, wooden trusses were no longer suitable for most railroad applications. In 1892, the C&NW replaced bridges across the Menominee and Escanaba Rivers with heavier steel structures, reusing the previous stone substructures. The replacement bridge consisted of five 135-foot, riveted quadrangular lattice through truss spans, which followed the standard Lassig Bridge & Iron Works design. In the early 20th Century, iron ore traffic over this line significantly increased, rendering early truss spans insufficient. In 1943, the C&NW undertook a project to reconfigure the bridge to allow for heavier loading. As part of the rebuild, the five spans were split in half and new piers installed. The bridge remained in this configuration for the remainder of its life, until it was ultimately replaced in 2015.

At the time of replacement, the bridge consisted of ten 67-foot, riveted, single track quadrangular lattice through truss spans, set onto stone and steel pile substructures. Initially, the truss spans consisted of standard Lassig-style lattice through trusses. When the bridge was reconfigured in 1943, the trusses were heavily altered by installing new endposts and portal bracing at the center of each span. Typical of early 1890s quadrangular lattice through truss spans constructed for the C&NW, the bridge used a combination of solid and built-up members with pedimented lattice portal bracings. The top chord was composed of a lightly built up beam, composed of two channels connected by thin plates, while the bottom chord was constructed of two parallel L-shaped beams. The original endposts consisted of a built-up design, with extensive X-lacing on the interior and a solid plate on the exterior. Conversely, the 1943-era endposts consisted of laced beams, which used X-lacing on both sides. The diagonal members used a combination of L-shaped bars, rolled beams and lightly V-laced built-up beams. The floor system used a standard design, with two steel stringers connected to floorbeams. The stringers appear to have been replaced when the bridge was reconfigured in 1943, and were clearly not the original members. Both the upper lateral bracing and the lower lateral bracing were constructed of L-shaped bars, which are riveted to the top and bottom chords. The original portal bracing used a pedimented Lassig style bracing, with a solid vertical plate in the middle and two X-lattice bracings on either side. The heel bracing was composed of decorative flower shaped cutouts in an angled plate. Unlike the original portal bracing, the 1943 portal bracing was purely functional, consisting of an M-frame design. The sway bracing used sqaure shaped bars, typical of spans from this era. To complete the alterations in 1943, a portion of the top chord was removed and new endposts were installed. The altered top chord was closed with an additional plate welded to the end. The original piers consisted of rectangular shaped structures, with a pointed face on the upstream side of the bridge. The 1943 piers consisted of several steel piles, connected by a concrete cap. Lassig Bridge & Iron Works fabricated the spans, while an unknown contractor completed the modifications and fabricated the new material. Unknown contractors also constructed the stone substructures and the steel pile substructures.

This type of truss design is relatively uncommon throughout the United States. However, a few railroads preferred the design, such as the Chicago, Rock Island & Pacific Railway (Rock Island), the Chicago & North Western Railway (C&NW) and the Chicago, St. Paul, Minneapolis & Omaha Railway (Omaha Road). Spans constructed in the late 1870s and early 1880s for the C&NW featured an arched and pedimented lattice portal bracing, light sway bracing and laced members. The second generation was nearly exclusively constructed by Lassig Bridge & Iron Works between 1884 and 1900, and featured heavier members and a decorative pedimented portal bracing. While the design fell out of favor for the Rock Island and Omaha Road around the turn of the 20th Century, the design remained popular with the C&NW into the 1920s. 20th Century versions of this design used significantly heavier members, were taller and contained no decorative features. The C&NW preferred this design, as it was both strong and demonstrated great resilience in case of a derailment. By the 2010s, the bridge had become too light for traffic, and the bridge was replaced in late 2015. The new bridge consists of modern welded plate girders, which reused the substructures with some alterations. At the time of replacement, there was reportedly severe deterioration to the trusses, which were apparently overloaded since the early 20th Century. The author has ranked this bridge as being regionally significant, due to the truss design, age and unique alterations.