Development of Ductile Segmental External Prestressed Concrete and Its Design Method

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The application of precast segmental structures with external prestressing is getting popular due to economical and time saving construction. However, since segmental externally prestressed concrete (SEPC) member shows brittle failure at the ultimate state, it has hardly been constructed in earthquake areas. When such a structure is applied to elevated bridge structures whose girders are fixed on top of the reinforced concrete bent and subjected to big earthquakes, some extent of ductility or deformation capacity of the girder will be required.In this study, the ductility improvement of SEPC beams has been developed, and analytical method to predict the load-deformation and design method for SEPC structures have also been established. An experimental investigation was conducted on a series of monolithic and precast segmental simply supported beams. The test variables were ; a) type of joint condition (dry or epoxy), b) provision of confinement reinforcements, c) method of prestressing (external or external together with internal bonded) and d) number of deviators (two or three). An analytical program that consists of an intensive iterative technique has been developed to predict the flexural behavior of the beams considering the material and structural non-linearities. The ultimate behavior of beams with dry or epoxy joints was nearly the same. There was a remarkable increase in the ultimate deflection for the beams with confinements. The experimental results were compared with the analytical predictions from the elastic range to the ultimate state. There was good agreement between them. From the above results it is concluded that the ductility could be improved by provision of confinements in precast SEPC beams and such structures can be erected in seismic areas. From many analytical results, design equations for flexural strength were proposed.