Nonlinear Analysis Of Shear Behavior Of Unbonded Prestressed Concrete Beams

Unbonded prestressed concrete beams have been widely used in building structures and bridge engineering.However,due to the complexity of the shear mechanism,there is still no recognized and unified shear theory that can provide a comprehensive and reasonable explanation of its shear strength.The design calculation formulas of shear capacity in various countries are mostly semi-empirical and semi-theoretical formulas based on a large number of test results.Because shear failure is sudden,it will cause a huge disaster once it occurs.Therefore,the research on the shear capacity of unbonded prestressed concrete beams is very urgent and important.In addition,since the unbonded prestressed tendons and the concrete of the section are deformed inconsistently,it is necessary to use numerical analysis to start from the overall deformation of the structure to make a detailed analysis of the cross-sectional stress of the unbonded prestressed tendons.This paper adopted the nonlinear finite element program ABAQUS to perform a nonlinear analysis of the shear behavior of unbonded prestressed concrete beams.The main work contents and conclusions are as follows:(1)The theory and numerical calculation method of concrete damage plastic model are introduced in detail.A set of combined concrete constitutive relations and damage factors are proposed and then verified by an example.(2)By introducing virtual prestressed tendons,rigid springs and local coordinate systems,a reasonable and more convenient simulation method of unbonded prestressed tendons is proposed,and its three parameters are analyzed to determine its reasonable value.(3)The influence of bending angle of prestressed tendons and longitudinal reinforcement ratio on shear performance of beams are analyzed from three aspects: load-displacement curve,stress change of prestressed tendons and crack development pattern.The influence of various parameters,such as concrete cube compressive strength,effective prestress,the form of prestressed tendons with or without bond,and the strength of ordinary reinforcements,are also analyzed.(4)This method can provide a reference for the nonlinear analysis of unbonded prestressed concrete structure,and the relevant analysis results can provide a reference for the optimal design of unbonded prestressed concrete beams.