Study Of Long Term Performance Of Simply-supported Internally And Externally Prestressed Concrete Girders

The external prestressing technology, ever used as a measure of reinforcement, has been developed to be adapted to construct initiative external prestressing structures. Much research on external prestressing technology has been accomplished at home and abroad, but little research focus on analysis of time-dependent girders deflection and stress of concrete and prestressed steel due to shrinkage and creep of concrete and relaxation of steel was fulfilled. In this paper, the age-adjusted effective modulus method is adapted to study the time-dependent effect of simply-supported prestressed concrete girders arranged with internal and external prestressed steel.Based on the characteristics of deformation between external prestressed steel and girder’s sections in anchor regions and deviators under the action of load, the formulae of incremental stress in external prestressed steel was established, the expression on time-dependent curvature of girder and stress and strain of concrete and steel are obtained. The relationship between the incremental elongation of external prestressed steel and stress of concrete in sections and sectional curvatures was deduced referring the characteristics of deformation between external prestressed steel and girder’s sections at any time. While combining with the internal force equilibrium along with the time-dependent relationship of concrete at any sections, an innovative analytical method on time-dependent effect in imply-supported concrete girders arranged with internal and external prestressed steel was presented, which considers synthetically the effect of shrinkage and creep of concrete, relaxation of internal and external prestressed steel sectional characteristics and steel ratio. Then, a set of formulae are established which can compute the stress and strain of concrete, long-term stress losses of internal and external prestressed steel and long-term deflection of beam.All established formulae are developed by FORTRAN language, and then an example is calculated both by the established formulae and by MIDAS software. The comparison of results shows that the presented method is feasible, the established formulae can be used to analyze time-dependent effects in simply-supported concrete girders arranged with internal and external prestressed steel.