This bridge is one of two similar but different deck arch bridges along this stretch of the Allegheny River. A structure of monumental size, this bridge carries 31st Street over the Allegheny River as well as various local streets. The main portion of the bridge is three steel deck arch spans, with the central span being the largest and having three hinges, while the smaller spans have two hinges. The approach spans are mostly deck plate girders. Among the approach spans, the spans at the northern end are most noteworthy. At the northern end of the bridge, there is a through girder span over the railroad which is partially concrete encased. This single span plate girder is highly unusual because the girders are spaced further apart at one end than the other, so that the roadway at the northern end of the bridge is wider. Just south of this girder span, their is a cantilevered deck plate girder with a suspended span that crosses the back channel of the Allegheny River.
This bridge was extensively rehabilitated in 2007, with an attractive blue paint placed on the bridge as well, replacing a former pale green color. The original ornate railings of this bridge were retained as part of this rehabilitation, representing the retention of an aspect of the bridge that is important both from an aesthetic standpoint as well as from a historic integrity standpoint. The rehabilitation of the main span superstructure was done very nicely, although it would have been nice to see the sway/lateral bracing members that were replaced on the bridge replaced in-kind. Those bracing members which were replaced are rolled beams with unusual punched shapes of ovals and hexagons, and do not match the original latticed built-up beams. On the approach system, the replacement of original material was more extensive, with many of the approach span superstructures being replaced completely. On the other hand, the substructure of the bridge including beautiful, massive built-up steel bents was retained. At the time of documentation, the railroad overpass span and the back channel span, both at the northern end of the bridge remained. However, these spans are slated for demolition and replacement as part of the continuing project which has been executed in multiple stages. The River Avenue Ramp which leads up to this bridge contains a substructure that is not part of the 31st Street bridge, but instead part of the previous 30th Street Bridge which provides access to Herr's Island. The previous 30th Street Bridge was a truss bridge, but it no longer remains, although the approach system remained at the time of documentation. This may also be removed however as part of the continuing rehabilitation project. Because it appears the majority of the structure at the northern end of the bridge
Although this rehabilitation did alter the bridge, the fact that the rehabilitation was so extensive should mean that with routine maintenance and repair, this bridge should be able to look forward to upwards of a century of service. The bridge remains today as one of the beautiful landmark bridges that makes Pittsburgh one of the greatest cities in the world for historic bridges.
During the field visit by HistoricBridges.org, the enormous plaques were missing from the decorative pillars of this bridge which rise above the roadway at piers on the main spans, but it is assumed these were being repaired and will be placed back on the bridge.
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