Analysis On Externally Prestressed Concrete Beams Prestress Loss And Second-order Effects Under Action Of Time-Dependent

External prestressing has a series of advantages such as reducing the dead weight of the structure,convenient replacement of external tendons and simple construction.It is widely used not only in strengthening old Bridges but also in building new ones.The biggest difference between in externally posttensioned members and internal posttensioned members is the external tendons are members for the normally elastic strain caused by the free silding between external tendons and deviators.Scholars have done a lot of tests and finite element analysis on external prestressed structures,but the external tendons themselves are rarely studied.In this paper,based on the verification of the external prestressed concrete simply supported beam model,the effects of time-dependent behavior,second-order effects,prestress loss,geometric nonlinearity on external prestressed concrete structures are studied.The effects of external tendons are expressed by equivalent nodal loads of the beam element、truss elements with rigid arms or multisegement-multinode in general,the principles of the above calculation models are briefly introduced.In this study,a numerical model based on the external tendons are members for the normally elastic strain caused by the free sliding between external tendons and deviators incorporating the existing line-elastic analysis programs is established.The present research status and achievements of concrete shrinkage and creep are summarized,the calculation formulas of external prestress loss in the JTG3362-2018 are adopted.The models of external prestressed simply supported beam and rigid frame bridge are established by using the large finite element software ANSYS.The accuracy of the iterative model and the feasibility of ANSYS modeling were verified by comparing the deflection and the external tendon stress of the basic model.Based on the establishment of ANSYS modeling,the arrangement of external tendons is transformed to compare the influence of second-order effects with time-dependent behavior under different specifications.The results demonstrate that the effect of second-order effects can not be considered in the external prestressed simply supported beam when two deviators are arranged,and the domestic specifications are conservative compared with the European specifications.Different simulation methods of external tendons have little influence on the mechanical properties of the structure,the simulation method of external tendons considering slip is more consistent with the actual situation.Compared with the geometric nonlinearity,the time-dependent behavior has a greater influence on the overall performance of the structure,but the geometric nonlinearity has a significant influence on the stress of external tendons.