Chestnut Street Overpass (Lodi)

View an article discussing this double tracking project (digitalized by Google)

Located in Lodi, this pony truss bridge carries Chestnut Street over the former Chicago & North Western Railway mainline, now operated by Wisconsin & Southern Railroad. It is unknown if an overpass previously existed at this location. During a double tracking project in 1896, a new overpass would be constructed at this location, using a secondhand pony truss span, approached by timber pile trestle spans and set onto stone pedestals and timber pile substructures. Records indicate there is some discrepancy if the present structure is the original 1896 structure, or if this structure was constructed later. Currently, the bridge consists of a 47-foot, 6-panel, riveted double intersection Warren pony truss span, approached by timber pile trestle spans. The bridge is set onto timber pile piers, which are supported by stone pedestals. The truss span appears to have originally been fabricated in approximately 1880 for railroad use at an unknown location. When the truss was moved here, it was heavily altered. An unknown contractor originally fabricated the truss, and an unknown contractor modified the span for roadway use. It is believed that John A. & George Garden constructed the stone pedestals, using stone quarried at nearby Rock Springs, Wisconsin.

Upon reuse, the truss span was heavily modified and likely shortened. The truss span uses a typical design for spans of this design, with light members and riveted connections. The top chord and bottom chord are both constructed using a T-shaped plate, indicating this span is older than similar spans which use built-up designs. The diagonal members are composed of simple L-shaped and T-shaped beams, without any lattice. It appears that the original outer panels of the span were removed, and the span may have originally been an 8-panel, 64-foot span. The current endposts consist of L-shaped vertical members, which appear to have been a modification. As part of the reconstruction, the original floor system was completely removed and rebuilt with a wider floor system. The current floor system consists of steel floorbeams, placed at the panel points. Additional wooden floorbeams are placed onto steel hangers, which have been installed on the altered bottom chord. In addition, additional steel plates appear to have been added to the bottom of the bottom chord upon reconstruction. Outriggers have also been added to the truss to help stabilize the floor system and truss webs. The deck of the bridge consists of timber planking, which has been overlaid with a bituminous surface. Railings on the approaches consist of a standard design, with three longitudinal boards supported by timber posts. The substructures use a typical design, with two square stone pedestals per pier. The piers are constructed out of one line of square lumber, and an additional timber pile has been driven between the stone pedestals for greater loading.

This type of span was popular with the C&NW from the mid-1870s into the late 1880s. This design provided a sufficiently strong iron span for early mainline use, and was particularly popular before heavier plate girders were developed in the early 1880s. A number of different variations of these spans were constructed, typically in standard 64-foot, 72-foot and 84-foot lengths. Early versions of this design used exclusively rolled members and did not have any significant lattice or built-up beams. Spans of this design were nearly exclusively constructed by the Leighton Bridge & Iron Works, and later the Alden and Lassig Bridge & Iron Works. Several 64-foot spans of this design were constructed for mainline use in Iowa between 1878 and 1880, and a handful of others were constructed along this line at the same time. This particular design was also popular for reuse as an overpass, as it could be easily modified to serve roadway use. Unlike other spans of a similar design, there is no evidence that this span was strengthened between its initial construction and when it was reused at this location. Railroads often reused steel and iron spans, as it provided a cost effective way to construct bridges without requiring large amounts of new material. Like many railroads, the C&NW reused steel and iron girder and truss spans for roadway overpasses, as these spans could easily be reconstructed and adapted for roadway use. Since the initial construction, the bridge has seen few alterations. The bridge was closed to automobile traffic in the 2000s, and remains open to pedestrian traffic only. Overall, the bridge appears to be in poor condition, with significant deterioration to the deck, main span and timber substructures of the bridge. It is likely that this bridge will eventually be demolished, with or without replacement. The author has ranked this bridge as being regionally significant, due to the age, design and unclear history.