Composite action in a steel girder span with precast deck panels :the I-81 bridge over the New River in Radford, Virginia

Two parallel bridges carry I-81 north and south over the New River in southwest Virginia, near the city of Radford. The bridges are identical in design and have been in place since 1985. In recent years, a number of maintenance issues have been reported, primarily related to cracking of the cast-in-place topping over partial-depth precast deck panels. A study was undertaken to determine the influence of the observed deterioration on the structural capacity of the affected bridge spans. The analysis indicated that the full potential of the composite slab-girder system is no longer being realized. Continued deterioration of the deck is likely, especially given the frequency of heavy truck traffic on this structure and the inherent vibration. It appears that the presence of precast cast-in-place deck sections has reduced the overall stiffness of the deck as compared to the original design. The movement, in conjunction with a poor deck panel support detail, is likely to cause a continual maintenance problem, as additional precast panels begin to move and fracture of the cast-in-place topping occurs. As a potential mitigation option, replacement of the fiber bolster material between the top flange of the girders and the precast panels with more rigid steel shims and/or concrete is recommended to increase the bearing surface of the panels, reduce vertical displacement of panel edges, and minimize dynamic impact at the joints.