IAIS Iowa River Bridge

Located in downtown Iowa City, this large deck plate girder bridge carries a former Chicago, Rock Island & Pacific Railroad (Rock Island) mainline over the Iowa River, Cedar Rapids & Iowa City Railway and US Highway 6. The first bridge at this location was likely a timber deck truss bridge, constructed when the line was first built. This bridge apparently had lengthy timber pile trestle approaches at either end, which spanned numerous streets and Ralston Creek. In 1869-1870, the Rock Island completed a major improvement project in Iowa City, filling the lengthy timber approaches. The Iowa River bridge was also reconstructed at this time with new stone piers and abutments, likely retaining the wooden deck truss design. In 1881, a new iron bridge was completed at this location. This bridge consisted of two 155-foot and one 152-foot pin-connected Pratt deck truss spans, approached by lengthy iron deck plate girder viaducts on either end. Between 1899 and 1902, the Rock Island invested significant capital into this line, replacing aging bridges with new steel and concrete structures. In 1901, the bridge was reconstructed with eight deck plate girder spans on new concrete substructures, and large portions of the viaduct approaches were filled. It is unclear if any portions of the previous bridge were reused, although a bridge in Estherville, Iowa potentially reused portions of the truss spans. When the new bridge was constructed, the substructures were constructed so that a second track could be added in the future, although this plan never came to fruition. In 1949, the bridge underwent a significant rehabilitation, including the addition of a timber pile trestle approach at the east end, the complete replacement of span #3 and the general rehabilitation to the remaining girder spans. Reportedly, the original span #3 was reused at an undisclosed location. The most recent alteration to the bridge came in 2023, when the timber pile trestle approach was replaced by concrete modular girder spans, giving the bridge its present configuration.

Currently, the bridge consists of two 78-foot, four 74-foot and two 70-foot deck plate girder spans, approached by two concrete modular girder spans on the east end. Almost the entire bridge is set onto concrete substructures, except for the east approach which is set onto steel pile bents. The main spans of the bridge use a standard design, consisting of two heavy plate girders and an open deck. The 1949-era span #3 is almost identical to the remaining spans, except for the steel is likely a different grade material and a longitudinal bracing is configured slightly different. All of the main piers use a standard rectangular design, which are likely founded on timber piles. It is unclear if any portions of the previous bridge were reused in the present substructure. The west abutment uses a standard design with sloped wing walls, and appears to have been constructed at a later date than the remaining substructures. The easternmost pier was originally the east abutment, and uses a stepped wing wall design with a demolished backwall. It is unclear why the east approach was added, although it was likely to improve erosion around the east end of the bridge. American Bridge Company fabricated most of the spans at their Lassig Plant in Chicago; while Bethlehem Steel Company fabricated span #3. It is believed that the piers were all constructed by railroad company forces, while it is unknown if the west abutment was constructed by railroad company forces or by an unknown contractor. The 1949 rehabilitation was carried out by railroad company forces, which removed, repaired and re-erected most of the spans. Deck plate girder spans were popular for railroad use, as they were durable and easy to construct. Since the initial construction, the bridge has seen minor alterations to the piers, particularly the reinforcement of the bases with sheet piling and concrete. Today, it remains in regular use as part of an Iowa Interstate Railroad mainline. Overall, the bridge appears to be in fair to good condition, with no significant deterioration noted. The author has ranked this bridge as being locally significant, due to the common design.