This locally administered federal aid project involved the rehabilitation of a historic steel truss bridge carrying Forest Home Drive over Fall Creek in the Town of Ithaca. Erdman Anthony provided the full range of services, including preliminary and final design, and construction support services.
The 117-foot span bridge was originally constructed in 1909 by the Groton Bridge Company and had undergone numerous rehabilitations and repairs over its lifetime. Erdman Anthony performed an in-depth bridge inspection and load rating analysis to determine the best rehabilitation approach for the project. These revealed that the previous addition of a cantilevered sidewalk and utilities had significantly reduced the live load capacity of the bridge and that a conventional rehabilitation approach would not remove the posted 15-ton load capacity.
To meet the project objective of an un-posted bridge, a less conventional rehabilitation scheme was developed. The existing roadway floor system was removed and replaced by a steel multi-girder superstructure with a composite concrete deck. The new superstructure spans the creek independently of the existing trusses, which remain in place. To minimize the impacts on the approaches, variable-depth girders were used for the superstructure. The top flanges of the girders follow the vertical curvature of the roadway and the bottom flanges are straight. The bridge roadway width between curbs is approximately 14 feet and the vertical clearance is 15 feet 4 inches. The bridge has a standard load capacity (45-ton design vehicle) and therefore does not require a weight restriction.
The new multi-girder bridge also carries utilities over Fall Creek. To ensure that the truss would no longer be burdened by loads beyond its own weight, all three bays of the bridge are used to carry the water, sanitary sewer, and gas lines between the community of Forest Home and Cornell University. A new pedestrian sidewalk was also designed to cantilever off of the upstream fascia girder, beneath the existing truss, to accommodate the high levels of pedestrian/bicycle traffic along Forest Home Drive.
New crosswalks and sidewalks provide easier access to the historic bridge and scenic views of Fall. Previously, pedestrians would have to share the narrow roadway with vehicles prior to crossing the bridge. Sidewalks have now been constructed at the approaches, providing increased levels of safety on the highly-used sidewalks in the Forest Home community and Cornell campus.
The historic truss structure underwent a significant rehabilitation as part of the project. The bottom chords of both trusses were replaced in their entirety due to significant deterioration. The end posts at the four corners of the truss were partially replaced and the entire truss structure was cleaned and repainted. Early in construction, the truss was moved to an area adjacent to the bridge site to construct the multi-girder bridge and repair to the truss. It was then moved back to its rightful place through a series of crane lifts.