Manitowoc High Trestle

Located on the northwest side of Manitowoc, this towering deck plate girder viaduct carries the former Chicago & North Western Railway mainline over the Manitowoc River. When the C&NW decided to construct a new cutoff between Manitowoc and Green Bay, the Manitowoc River Valley represented a significant challenge. Due to the elevations required for the new railroad, it was decided to construct a large deck plate girder viaduct. Work on the bridge began in 1905, and the structure was initially completed in 1906. Initially, the bridge consisted of a 60-foot deck plate girder, a 100-foot deck plate girder, 14 spans of alternating 65-foot spans and 35-foot tower spans and an additional 65-foot deck plate girder span on the north end. The bridge was set onto stone piers and large steel towers, and was approached by short timber pile trestle approaches at either end. Timber approaches were commonly used by the C&NW on new bridges, as it allowed large approach embankments to settle without damaging permanent structures. In 1938, the southern 60-foot and northernmost 65-foot spans were removed, and new deck plate girder approaches were constructed, giving the bridge its present configuration. It is likely that the original 60-foot and 65-foot spans were reused elsewhere on the C&NW system.

Currently, the bridge consists of several different sized deck plate girder spans, set onto stone piers, steel towers and concrete pile piers. The south approach consists of a 45-foot span (span #1), a 50-foot span (span #2) and a 100-foot span (span #3). The main portion of the bridge consists of fourteen alternating 65-foot and 35-foot spans (spans #4-#17), while the north approach consists of a 50-foot span (span #18) and two 30-foot spans (spans #19 and #20). Piers #2 through #17 are constructed of stone masonry founded on timber piles, with piers #4 through #17 serving as footings for the large steel towers. Piers #1, #18 and #19 are constructed of concrete capped concrete pile piers, and the abutments are also constructed of concrete pile structures. The main spans (spans #3 through #17) use a standard design, and are constructed of two heavy plate girders with an open deck. The approach spans appear to use slightly different designs, with shallower girders. It is believed that spans #1, #2, #18, #19 and #20 may have been reused here from other locations, and likely were fabricated in approximately 1910. The towers are heavily constructed, with two trapezoidal bents at each member, which are connected by two levels of longitudinal bracing on either side. All members of the tower are composed of built-up beams constructed with various V-lacing designs. Piers #2 and #3 are constructed using a tall rectangular design, while piers #4 through #17 consist of short rectangular piers with angled fenders on both sides. The superstructure contains a walkway on both sides, which is supported by brackets attached to the girders.

A number of different contractors contributed to constructing the bridge. American Bridge Company fabricated spans #3 through #18 at their Ambridge Plant in Pennsylvania. Unknown contractors fabricated the approach spans, and it is possible that these spans were fabricated by a number of different contractors. Adolph Green Construction Company was awarded a $75,000 contract for constructing the stone piers of the bridge. Stone for these piers appears to be a white limestone, likely quarried at the C&NW-owed quarry in Duck Creek, Wisconsin. It is unknown if the concrete substructures were constructed by an unknown contractor or by railroad company forces. Deck plate girder spans were commonly used by railroads, as they were durable and easy to construct. Large deck plate girder viaducts such as this were the most economical way to carry railroads over large valleys, as they required the least amount of material and had a simple design. Concrete pile foundations became popular in the mid-20th Century, as the piles could be cast off-site and easily installed without significantly impacting railroad traffic. Since the 1938 revisions, the bridge has seen no significant alterations, and remains in 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 size.