BNSF Skunk River Bridge (Rome)

Located east of Rome, this large deck truss bridge carries a former Chicago, Burlington & Quincy Railroad mainline over the Skunk River. Originally, the CB&Q mainline ran on a different alignment between Mount Pleasant and Rome, crossing the present mainline near the east end of this bridge before running southwest and crossing the Skunk River approximately 2,800 feet downstream. The first bridge at that location was likely a wooden truss bridge, constructed when the line was first built. It is believed that an iron through truss span was constructed on stone piers in the late 1870s or early 1880s. Between 1899 and 1904, the CB&Q realigned and double tracked their mainline through southern Iowa. As part of the work, the railroad was straitened between Mount Pleasant and Rome, and a new bridge was constructed on a new alignment between 1899 and 1900. By the early 1930s, many bridges along this line had become too light for traffic, and would need to be rebuilt or strengthened. In 1931, the bridge was rebuilt by replacing the west truss span with a new truss span, reusing the truss lines in the center span and rebuilding the east truss span with secondhand truss lines from an identical bridge over Big Creek near Mount Pleasant, Iowa. Further alterations were made to the bridge through the 1930s to strengthen the spans and add a ballast deck. In addition, the main piers were encased with concrete at some point in the mid-20th Century, giving the bridge its present configuration. Currently, the bridge consists of two double strength 146-foot, 7-panel, pin-connected Pratt deck truss spans (east and center span) and a 146-foot, 7-panel, riveted Pratt deck truss span (west span). The bridge is approached by two 60-foot and one 29-foot deck plate girder spans on the east end and four 60-foot, one 70-foot and five 29-foot deck plate girder spans on the east end. The main piers of the bridge are constructed of stone which has been encased in concrete, while the abutments and pedestals are constructed exclusively of concrete.

The east and center truss spans all follow a modified standard design, with heavy built-up members, a standard floor system and pinned connections. Both truss spans contain four total truss lines, arranged into two sets of two. The top chord and endposts consist of built-up beams, consisting of a box-shaped beam with V-lacing on the bottom and a solid plate on the top. The bottom chord uses two distinct designs, with a V-laced beam at the outer panel on each end and eyebars at the remaining panels. The vertical members all consist heavy V-laced beams, while the diagonal members all consist of eyebars. Most of the diagonal members are formed from steel bars, while the counters are formed from steel rods. Lower transverse bracing between the inner trusses consists of V-laced beams, while solid plates are used between adjacent truss lines. In addition, a wooden spacer is present at areas to separate the trusses. The floor system is composed of heavy plate girder floorbeams set above the trusses and four heavy plate girder stringers. The western truss span follows a different design, which is more typical for the 1930s. Both the top chord and bottom chord are composed of built-up beams with V-lacing on both sides, while the endposts are composed of solid beams. The vertical members are constructed using two different designs, with V-laced beams at the center posts and beams consisting of L-shaped bars connected by thin plates at the hip posts. The outer diagonal members are composed of solid beams, while the center diagonal members are composed of V-laced beams. All lower lateral and transverse bracing is composed of simple square bars. Similar to the east and center trusses, the floor uses plate girder floorbeams and plate girder stringers.

The approach spans are all simply composed, consisting of two heavy plate girders per track and standard X-frames and lateral bracing. The 29-foot tower spans are significantly more shallow than the main spans, typical of this type of viaduct. At the towers, the 29-foot spans are supported by short triangular risers. The approach spans have had much of the original bracing replaced with new riveted bracing to strengthen the spans. The entire bridge is covered by a creosoted timber ballast deck. At the ends of the truss section, the girders are supported by an A-frame bent, which is composed of V-laced beams and has been strengthened with a solid beam through the center. The towers are constructed of four angled posts, with a transverse plate girder at each side. Each post is composed of a built-up beam with V-lacing on the interior and a solid plate on the exterior. Both longitudinal and lateral bracing are present, and are composed of light built-up beams. The main piers use a standard rectangular shape with angled upstream noses. All pedestals consist of standard square shapes, while the abutments use a standard design with short sloped wing walls extending perpendicular from the bridge. All of the substructures are founded on timber piles, and many portions of the substructures have seen concrete repairs since the initial construction.

A handful separate contractors are believed to have worked on constructing this bridge. King Bridge Company fabricated the deck plate girder spans and the east and center truss spans, while Vierling Steel Works fabricated the west truss span. It is unclear if the strengthening of the truss spans and the alterations to the girder spans were completed by railroad company forces or by an unknown contractor. The original substructures are believed to have been constructed by railroad company forces, and it is unclear if the alterations to the main piers was completed by railroad forces or by an unknown contractor. King Bridge Company constructed a number of bridge spans for the CB&Q, primarily in the late 1890s and early 1900s. Vierling Steel Works primarily constructed short beam and girder spans for the CB&Q, and it is unclear if additional trusses were constructed by this firm. The Pratt pattern was arguably the most popular truss design for railroad bridges in second half of the 19th Century, as it was strong, simple and economical. Around the turn of the 20th Century, the Pratt pattern was largely superseded by riveted Warren designs. It is unclear why a riveted Pratt design was chosen for the west truss span, and this appears to be a unique feature to this bridge. Since the mid-20th Century, the bridge has seen no notable alterations. Today, the bridge remains in use as part of a heavily used BNSF Railway mainline. Overall, the bridge appears to be in fair to good condition, and appears to be well maintained. The author has ranked this bridge as being regionally significant, due to the large size and unique alterations.