Peshtigo Railroad Bridge (South)

Located in Peshtigo, this large through truss bridge carries the former Chicago & North Western Railway mainline over the Peshtigo River. The first bridge at this location was likely a wooden through truss bridge, constructed when the line was first built. In the late 1870s and early 1880s, the C&NW made significant improvements to this line, replacing early timber structures with heavier bridges. In 1881, the bridge was rebuilt with two 127-foot and one 99-foot riveted quadrangular lattice through truss spans, set onto stone substructures. These wrought iron trusses likely used a design typical of late 1870s and early 1880s lattice truss spans, with light members and an attractive arched lattice portal. It is likely that the iron trusses were strengthened in the early 20th Century as loads on this became heavier. By the late 1910s, the bridge had become too light for the heavy traffic using this line. Plans were made to replace this bridge as early as 1916, and it is believed the structure was replaced by the present bridge around 1920. It is unknown if the 1881 spans were reused elsewhere, but it is possible at least the center span was reused at Carpentersville, Illinois. Many railroads, including the C&NW, reused steel and iron spans for branch line structures, as this reduced the cost and amount of new material required for constructing branch line bridges.

Currently, the bridge consists of two 127-foot and one 99-foot riveted quadrangular lattice through truss spans, set onto stone substructures. When the present bridge was constructed, the substructures were retrofitted with concrete pads on the tops to repair stone which had likely deteriorated. The trusses follow a standard design for the era, with heavy members, a traditionally composed floor and an A-frame portal. Both the top chord and bottom chord are constructed of built-up beams, consisting of V-laced channels. The bottom chord is V-laced on both sides, while the top chord is V-laced on the bottom with a solid plate on the top. Similar to the top chord, the endposts use a combination of V-lacing and solid plates on the bottom, while the exterior is covered by a solid plate. Diagonal members of the outer trusses consist of a combination of tightly V-laced beams, rolled beams and steel L-bars. The center span omits the V-laced beams, and instead uses solid bars and L-shaped bars. The floor of all spans is heavily constructed, with plate girder floorbeams at the panel points and two plate girder stringers. The bottom lateral bracing is composed exclusively of L-shaped bars. The portal bracing uses a standard A-frame design, which is constructed out of V-laced beams. Similar to other structures from the era, the sway bracing and upper lateral bracing are both composed of V-laced beams. Also similar to other bridges along this line, the piers use a diamond shape with a heavier deflector on the upstream side. The abutments also use a standard design, with stepped wing walls extending diagonally from the structure. Stone for the substructures consists of a white limestone, possibly quarried at Duck Creek, Wisconsin. An unknown contractor fabricated the superstructure, while unknown contractors constructed the stone substructures and completed the concrete repairs.

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. 19th Century versions of this design were primarily constructed out of wrought iron, while 20th Century versions of this design were constructed of steel. The C&NW preferred this design, as it was both strong and demonstrated great resilience in case of a derailment. Since the c. 1920 construction, the bridge has seen no significant alterations and remains in regular use. Overall, the bridge appears to be in fair to good condition, with no significant deterioration noted. The author has ranked this bridge as being moderately significant, due to the truss design and unknown history.