Manitowoc Low Trestle

Located near Clay Pit Road on the north side of Manitowoc, this through plate girder and steel stringer bridge carries the former Soo Line Manitowoc Branch over the Manitowoc River. When the Wisconsin Central Railway reached Manitowoc in 1896, a bridge was required across the Manitowoc River at this location. Initially, the bridge consisted of two through plate girder spans, set onto timber pile piers and approached by timber pile trestle approaches on either end. In approximately 1940, the main spans were shifted onto newly built timber pile piers, and three steel stringer spans were added to the east end and two steel stringer spans were added to the west end. During the 20th Century, this bridge was the scene of numerous fires, due to its mainly timber construction. The most serious of these fires occurred in 1991, when a large portion of the east approach was burned. In response, the remaining timber pile trestle sections of the east approach were replaced by additional steel stringer spans soon after the fire. Additional repairs appear to have been made in the 1990s or early 2000s, including the replacement of several piers with steel pile bents, giving the bridge its present configuration.

Currently, the bridge consists of two 75-foot through plate girder spans, set onto steel pile west and center piers and a timber pile east pier. The west approach is comprised of two 37-foot steel stringer spans and three timber pile trestle spans, which are set onto a combination of steel pile and timber pile substructures. The east approach is comprised of three 37-foot steel stringer spans, which are set onto timber pile piers. These spans are approached by a 10-foot steel stringer span, a 25-foot steel stringer span and three 27-foot steel stringer spans, which are set onto steel pile piers with concrete caps. The east end of the bridge is set onto a 3-degree curve, and all steel spans are constructed at a heavy skew. The through plate girder spans use a standard design for the era, with heavy girders, an open deck floor and square girder ends. Unique to these spans, the end floorbeams are composed of lattice girders, a design sometimes used on 19th Century girder spans. Steel stringer spans on the approaches use a variety of different designs, reflecting the different dates they were installed. The The 37-foot spans use a shallow design, with four beams per span. These spans appear to have been fabricated in approximately 1940, and are likely original to this location. The short 10-foot span on the east approach serves as a jump span, and likely was reused as scrap from another location. The 25-foot and 27-foot spans on the east approach also use shallow beams, but contain bolts instead of rivets and likely were fabricated in the late 1980s or early 1990s, and installed here after the 1991 fire.

Typical of bridges on this line, Wisconsin Bridge & Iron Company fabricated the main spans, while the approach spans were fabricated by unknown contractors. All substructures appear to have been constructed by railroad company forces. Through plate girder spans were commonly used by railroads, as they were durable and easy to construct. Because of the numerous alterations and lack of available plans for this bridge, it is difficult to estimate the date of additional alterations, such as the installation of the steel piers. In addition, many of the timber piles were not cut off below the water line, further adding to the unusual appearance of this structure. Overall, the bridge appears to be in fair to good condition, with some deterioration noted mainly to the timber piers. The author has ranked this bridge as being locally significant, due to the common designs.

Authors Note:
This line also crossed the Manitowoc River on two additional bridges, located near the Burger Boat Company. The western bridge consisted of a 180-foot, 7-panel, pin-connected Pratt through truss swing span, approached by timber pile trestle spans. This bridge was also fabricated in 1896 by the Wisconsin Bridge & Iron Company, and consisted of an extremely lightweight truss arranged in what appeared to be a center-bearing configuration. The eastern bridge was constructed in 1926-1927 by the American Bridge Company, and used an Abt style bascule lift span with a through plate girder main span. After the line was abandoned in the early 2000s, the bridges were placed in open position and remained unused. Due to the unusual curve in the river and the obstruction to navigation for industries, the bridges were removed in 2011. The author is including this blurb due to the significance of these two structures and their unfortunate demolition.