UP Le Sueur Creek Bridge

Located just north of Le Sueur, this unique pony truss bridge carries the former Chicago, St. Paul, Minneapolis & Omaha Railway mainline over Le Sueur Creek. The first bridge at this location was likely a timber pile trestle. In the 1870s, the bridge was replaced by a 48-foot wooden pony truss span, set onto stone piers and approached by timber pile trestle. The bridge was again upgraded in 1892, when a new 48-foot iron deck plate girder span was constructed to replace the wooden truss. During the late 1890s and early 1900s, the Omaha Road invested significant capital into this line, realigning the route and replacing outdated bridges. In 1899, the Omaha Road constructed a new alignment north of Le Sueur, replacing the original bridge. As part of the work, a four span pony truss bridge was constructed at this location. The truss spans were constructed using pieces of an older bridge, reused from another location. After the new line was completed, the old bridge was removed. It is unknown if the iron girder span was reused elsewhere. The southern two pony truss spans were removed prior to 1938, giving the structure its present configuration. It is unknown if the removed truss spans were reused at another location or scrapped.

Currently, the bridge consists of two 84-foot, 7-panel, riveted double intersection Warren pony truss spans, set onto stone and concrete substructures. The trusses for this bridge were originally fabricated in 1881 as part of a 10 span approach for the St. Croix River bridge at Hudson, Wisconsin. After that bridge was replaced, the ten spans were combined into five double-barreled spans, reusing two truss spans per reconstructed span. Four of the five spans was reused at this location. The remaining span were reused at a bridge in Clark County, Wisconsin, which continues to exist today. The trusses were originally fabricated by the Leighton Bridge & Iron Works; while an unknown contractor reconstructed the span. An unknown contractor constructed the substructures using limestone quarried at Mankato, Minnesota. An additional unknown contractor constructed the concrete repairs to the substructures, which included converting the center pier to the new south abutment. Later revisions included masonry repairs in 1977.

Except for the floor and vertical members, all material of the spans appears to be original to the 1881 spans. The upper chords and endposts consist of iron channels, connected by thin plates. The bottom chords are composed of parallel iron channels, which are riveted together on the bottoms. Typical of early spans of this design, some diagonal members use a built-up design, with a tight X-lacing. The remaining diagonal members consist of iron L-bars. Because the spans are double-barrelled, the top chord, bottom chord, endposts and diagonals are constructed of two parallel and identical sets of members. The floorbeams of the bridge consist of a tapered girder, while the stringers use a stringer design. Lower lateral bracing is composed of iron bars, which also appears to have been reconstructed in 1899. In addition, the vertical members appear to have been constructed of new material in 1899, replacing the original iron bar vertical members. It is likely that the floor and vertical members are constructed of steel, while the remainder of the trusses use wrought iron.

This style of truss was commonly used by the Omaha Road, the Chicago & North Western Railway (C&NW) and a handful of other railroads throughout the United States. This design was developed in the 1870s, and provided a strong design without requiring large amounts of new material. In addition, the design was among the first pony truss to use riveted connections. These spans were optimal for spans in the 60-foot to 100-foot range. Many railroads moved away from this design by the late 1880s, as technology allowed for heavier trusses and longer plate girders. Leighton Bridge & Iron Works, the fabricator of the Hudson bridge, was an early pioneer in developing this design. This company constructed numerous lattice trusses of various designs for the Omaha Road and the C&NW in the late 1870s and early 1880s. Many spans of this design became too light for traffic by the turn of the 20th Century, and would be reused on branch lines or for overpasses. This particular span represents an early example of this design.

Most United States railroads reused steel and iron spans, as it was a way to save money on bridge replacements. Often, when a span became unsuitable for mainline use, it was feasible to reuse on a branch line, where lower loading requirements were required. Many of these spans were either strengthened or rebuilt, as was the case with this bridge. Doubling truss spans was a technique occasionally used by railroads to increase loading of old truss spans. Often, when spans were doubled, a new floor system was required. This work was typically done by a contractor in a bridge shop. Since the south spans were removed, the bridge has seen few alterations. The bridge remains in use for mainline traffic today. Overall, the bridge appears to be in fair to good condition, with some deterioration noted to the substructures. The author has ranked this bridge as being highly significant, due to the design, age and builder of the span. The trusses on this bridge are among the oldest remaining spans of this design in the Midwest.