RCP&E N. Fork Bad River Bridge

Located in Philip, this pony truss bridge once carried the Black Hills Division of the Chicago & North Western Railway over the North Fork Bad River. The first bridge at this location consisted of a 106-foot wooden Howe through truss span, approached by timber pile trestle on either end. During the late 1920s and early 1930s, the C&NW invested significant capital into this line, replacing outdated timber bridges with mainly secondhand steel and iron spans. In April 1927, plans were made to replace this bridge with a 142-foot iron quadrangular lattice through truss span, reused from the Mississippi River Bridge at Winona, Minnesota. Soon after the plan was approved, the 142-foot truss span was no longer available for use, and the plan was substituted to use a secondhand iron pony truss span. Work on the replacement bridge began in July 1927, and the new bridge was completed in August 1928. The bridge consisted of an 84-foot, 7-panel, riveted double intersection Warren pony truss span, approached by timber pile trestle spans on either end. The truss span was placed onto steel cylinder piers, which were filled with concrete, while the remainder of the bridge was set onto timber pile substructures.

The history of the truss span is not clear. It is believed that the span was originally fabricated in approximately 1885, likely for use on a mainline in Illinois, Wisconsin or Minnesota. The truss span at its original location was replaced in approximately 1910, and the truss span was installed at Bridge #K-3A in 1911, which carried a mine spur across Whitewood Creek in Deadwood, South Dakota. After the spur was removed in approximately 1925, the truss span was shipped to the bridge yard in Chicago, before being reused here. Based on the design, it is believed that the truss was initially fabricated by the Alden and Lassig Bridge & Iron Works. The steel cylinder piers were constructed by Peppard & Burrill, which was contracted to complete bridge improvements on the Black Hill Division for the 1927 construction season. The truss span used a standard design for the era, with built-up compression members, riveted connections and modestly deep trusses. The top chord, bottom chord and endposts all used a channel design, and the top chord and endposts were connected by a plate on the top. The compression members consisted of X-laced built-up beams, while the tension members and vertical members used L-shaped iron bars. The floor was comprised of four I-beam stringers arranged into two sets of two and plate girder floorbeams set at the panel points, typical of spans from this era. It is unclear if the span was modified from its original design during either of its known relocations.

Railroads commonly reused steel and iron spans, as it was a cost effective way to replace bridges on branch lines and spurs without requiring large amounts of new material. Often, when a span was no longer adequate for mainline use, it could be reused on a branch line with minimal alterations. Pony truss spans such as this were used extensively by the C&NW throughout the 1880s, as they were durable, simple and cost effective. Dozens of similar spans were constructed for the C&NW, with most spans constructed by Leighton Bridge & Iron Works (1870s-1881); Alden and Lassig Bridge & Iron Works (1881-1885) and Lassig Bridge & Iron Works (1886-c. 1890). The design was ultimately superseded by heavier plate girder bridges, which were stronger and equally economical. Since the 1927-28 relocation, few alterations appeared to have been made to the truss span and bridge overall. The bridge was destroyed in a derailment on the evening of January 27th, 2022 and was later replaced by a steel stringer bridge. Overall, the bridge appeared to be in fair condition at the time of documentation, with minor deterioration noted throughout the structure. The author has ranked this bridge as being regionally significant, due to the lack of pony trusses in South Dakota, as well as the relocation history.