United States Department of Transportation
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Abstract:Prestressed concrete girder bridges are generally made continuous by adding longitudinal reinforcement in the deck over the pier. With this continuity method, the superstructure is continuous only for one-third of the total load. The pier diaphragm, which is normally cast prior to the deck, may experience distress because no negative moment resistance is available as the deck is being placed. An innovative threaded rod continuity system was introduced to make the precast girders continuous for deck weight. Based on the connection detail developed in a previous NDOR project titled “Superstructure/Substructure Joint Details,” a standard bolted connection detail was proposed to couple the precast girders. The precast girders are made continuous for approximately two-thirds of the loads, which results in reduced demand for prestress and for high strength concrete at release. The same girder size can span about 15 percent longer than the conventional system. Bridge performance is improved as the negative moment due to deck weight more than offset the positive moment due to time-dependent restraint without causing cracking at the piers. The Clarks Viaduct is the first bridge in the United States to use the threaded rod continuity system. Its completion showed that this system is easy to construct without need for a specialty contractor. The system provides a feasible and cost-effective alternative for concrete superstructures to compete with long span steel bridges.
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