Time-varying Coupling Effect And Programming Of Normal Concrete Bridge

Shrinkage and creep effect,prestress loss and geometric nonlinear effect are the main influencing factors for the insufficient analysis accuracy of the bridge life cycle,which have a direct impact on the long-term monitoring of the structure.The development trend of long-span,lightweight and towering bridge structure puts forward higher requirements for structural finite element theory and calculation method.In this paper,the response mechanism of prestressed concrete bridge under long-term effect is studied from three aspects:relaxation of prestressed reinforcement,shrinkage and creep of concrete and geometric nonlinear change of structure.(1)For the reconstitution of the prestressed tendon due to the prestressed loss,the prestressed tendon is regarded as an eccentric truss element with rigid arms at both ends,which is connected with the corresponding element nodes.In the stage of prestressed application,the prestressed tendon and the beam are regarded in unbonded state,and only the equivalent node load caused by effective stress is considered in the structural global equilibrium equation.In all solving steps before the passivation of prestressed reinforcement,the prestressed reinforcement and the element are regarded as completely bonded.The calculation process is summarized and the complete calculation program is compiled.The calculated result of prestressed loss is verified in good agreement with the example datas.(2)Dirichlet series is used to fit the creep function.Two different expressions of creep strain are derived according to the two assumptions that the internal stress characteristic of time step is constant and the internal stress characteristic of time step is linear.The finite element calculation program is developed to compare the calculation results.Xincheng bridge in Lengshuijiang,Hunan Province(2×149m),a single tower cable-stayed bridge,is taken as the engineering background.Different shrinkage and creep prediction models are used to analyze the deflection and cable force under the shrinkage and creep effect,and the differences between various shrinkage and creep prediction models are compared.The results show that JTG D60-2004 shrinkage and creep calculation model is suitable for the analysis of shrinkage and creep effect of cable-stayed bridges in operation period.(3)For structural geometric nonlinearity,by using the co-rotational finite element procedure,the geometric nonlinearity of the plane beam element is calculated.The relationship between the end force and the node displacement between the rotating coordinate system and the structural coordinate system is derived based on the differential method,and the stability function is innovatively combined.The total equilibrium equation and tangent stiffness matrix of geometrically nonlinear plane beam element in structural coordinate system are derived.On this basis,the tangent stiffness matrix of the element considering the beam end with hinge is derived.Through the numerical examples results,the analysis method based on co-rotational procedure shows good accuracy in geometric nonlinearity and buckling problems,and is more suitable for the compilation of self-developed programs.The time-varying nonlinear analysis algorithm of concrete-filled steel tubular(CFST)arch is established by combining the initial strain method for creep effect analysis,and the finite element program is developed.The creep calculation formulas of core concrete in steel tube and ordinary concrete in Chinese codes are adopted respectively for analysis.Based on the verification of the analytical solution of an example of hinged CFST arch with obvious time-varying nonlinear behavior,the time-varying linear and nonlinear comparative study of CFST bridge with main span of 368m is carried out.