J Avenue Overpass

Located east of Ogden, this historic pony truss bridge carries J Avenue over a former Chicago & North Western Railway mainline. Originally, the C&NW line turned southwest at Boone, following the Honey Creek valley, crossing the Des Moines River at Moingona and turning northwest towards Ogden. This original line had steep grades, several curves and was overall poor for operations. Starting in 1899, the C&NW sought to double track the line between Cedar Rapids, Iowa and Council Bluffs, Iowa. As part of the project, a double track cutoff was planned between Boone and Ogden, which would include a tall viaduct over the Des Moines River. Work on the cutoff began in 1899, and the line was opened in early 1901. To safely carry wagon traffic over the new railroad, two pony truss overpasses were constructed at L Avenue east of the viaduct and J Avenue west of the viaduct. The overpass at J Avenue was constructed in 1900, using a secondhand pony truss span which was reconstructed to handle a wider deck.

The overpass consists of a 75-foot, 7-panel, riveted wrought iron double intersection Warren pony truss span, set onto timber pile piers supported by stone pedestals. Each end of the pony truss is approached by two timber pile trestle spans, giving the bridge a distinct "humpback" shape. In addition, the truss is set at a heavy 45-degree left skew, and the deck is constructed at a width of 18 feet. The truss span was originally fabricated in approximately 1882 for use at Bridge #217, which carried the Madison Division across an unnamed creek north of Oregon, Wisconsin. That bridge originally consisted of a 75-foot truss span, which was replaced by a shorter double track steel stringer span in 1898. Annual reports of the Chicago & North Western Railway indicate that four trusses were constructed at various points on the Madison Division in 1881-82. Other reports do not indicate that any iron trusses were constructed between Evansville and Madison from 1877 to 1885. Upon reuse at this location, the truss span was heavily altered, including the complete replacement of the original floor system and the addition of outriggers to help support the reconstructed floor. It is believed that the truss was originally fabricated by either Leighton Bridge & Iron Works or its successor, the Alden and Lassig Bridge & Iron Works. The Alden and Lassig Bridge & Iron Works was formed in late 1881 to take over the shops of the Leighton Bridge & Iron Works in Rochester, New York; and this firm opened a shop in Chicago soon after. The C&NW extensively contracted with these firms for iron bridges in the late 1870s and early 1880s. An unknown contractor reconstructed the truss span upon relocation, and it is unclear if the alterations were made in the field or at a shop. As part of the alterations, the truss was converted from a standard span to a heavily skewed span. The Widell Company constructed the stone pedestals as part of a larger contract for all stonework required between Boone and Ogden.

The truss span follows a standard design for the era, with light members and riveted connections. The top chord, bottom chord and endposts all use T-shaped beams, which are formed by riveting together plates and angles. The diagonal members consist of L-shaped bars, with some members using one bar and others using two bars riveted together. These diagonals are riveted to the top and bottom chords on alternating sides. Hip verticals are present on this span, and consist of two L-shaped bars which are riveted together. The floor system consists of numerous parallel timber beams, which are supported on the bottom chord by use of brackets, which were installed during the 1900 reconstruction. The northeast and southwest corners of the truss use timber stringers, which are integral with the approaches and were added to accommodate the skew of the span. The entire truss is held together by five sets of outriggers, which connect the top chord to thin transverse I-beams, which are riveted to the bottom chord. The piers consist of two rows of bents, which are supported by large rectangular stone pedestals. The piers use square lumber, while the approach bents and abutments use round piles. The approach spans consist of timber stringers, which are supported by bents. The entire deck of the bridge consists of wooden planks, and wooden railings are present on the structure. In addition, timber curbing is used at the edges of the roadway. Also unique to this bridge, the entire structure is slightly superelevated, pitching towards the east.

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. This span is unique for having used a 75-foot length, a non-standard design. 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. This particular design was also popular for reuse as an overpass, as it could be easily modified to serve roadway use. 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 mid-20th Century, a vast majority of these historic overpasses have been removed or replaced. Unfortunately, many of these overpasses used some of the oldest truss and girders available for reuse, with many dating to the early 1880s or before. Since the original construction, the bridge has seen relatively few alterations, and today it remains in use carrying a limited amount of automobile traffic. Overall, the bridge appears to be in fair condition, with most of the timber components showing relatively little deterioration. However, the original iron components of the truss span remain in fair to good condition. It is likely that this bridge will eventually be demolished and replaced. If this bridge is demolished, the truss span could feasibly be repaired for pedestrian or light motorized vehicle use. The author has ranked this bridge as being highly significant, due to the age and design.