Rehabilitation of Bridge Superstructures via the Addition of Girder Lines. I: Theoretical Considerations

The Alabama Department of Transportation (ALDOT) currently maintains over three miles of interstate bridges near downtown Birmingham with significant levels of deck cracking and deterioration. The rehabilitation of these bridges is a matter of great concern to the ALDOT because of the enormous cost and potential for disruptions of traffic. The most viable rehabilitation options at this time appear to be (1) to rehabilitate the bridge decks via overlays; (2) to replace the decks; (3) to add additional longitudinal girders; or (4) to replace the bridge superstructures. The purpose of the research reported in this paper was to investigate and evaluate the option of adding additional longitudinal girders as a bridge deck/superstructure rehabilitation strategy on the existing bridge decks, support girders, bent caps, and foundation elements. Results of the analysis indicate that adding girders is a structurally viable strategy. Particular benefits include doubling the capacity of the deck membrane arching capacity, significant reductions in the superstructure deflections, and an increase in the remaining fatigue life of the existing bridge girders by approximately a factor of eight.