Creep,Numerical Inverse Of Static-Dynamic Problems For The Viscoelastic Structures And The Application Of Viscoelastic Dampers In Earthquake Resistance

In this thesis, the viscoelastic laminated plates,cylindrical shells and viscoelastic dampers are investigated. The application of DAC method based numerical Laplace inverse transformation in viscoelastic mechanics problems is introduced and studied. Then the behavior of failure and creep deformation are analyzed for thin viscoelastic plates coupling anisotropic damage. At last, the effect of earthquake resistance for cable-stayed bridges with viscoelastic dampers is investigated. The main research contents and results are given as follows.The application of DAC method based numerical Laplace inverse transformation in viscoelastic mechanics problems is studied. The optimal model to determine calculation parameter in DAC method is constructed. As examples to illustrate the practical implementation of the proposed method, the quasi-static and dynamic analysis, within the scope of axisymmetric problem, are performed for viscoelastic laminated circular cylindrical shells under uniformly axial pressure and viscoelastic cylinder subjected to inner pressure with abrupt loading respectively, and a simple rule is observed in numerical experiments for choosing that parameter. According to Donnell shallow shell assumption and Kármán-Donnell geometrical nonlinear relationship, the quasi-static analysis and dynamic investigation are performed for viscoelastic laminated circular cylindrical shells under abrupt loading of uniform external pressure by numerical Laplace inverse transformation. Some features of the deflection and circumferential membrane force are given.Assuming the coincidence of principal directions of stresses tensor with that of damage tensor, the hereditary constitutive equations coupling anisotropic damage are constructed based on Schapery's correspondence principle with damage growth. The thin wall structure is modeled as the lamination of finite laminas along the thickness of structure and Kachanov's evolution kinetics is adopted to describe the progress of damage in two principal directions at any point of laminas. Resulting nonlinear governing equations and boundary conditions expressed in the form of deflection and in-plane displacements of plate are discretized in space domain by means of finite difference technique and associated convolute integrations are obtained at discretized points by numerical integration, and finally the iterative calculation of nonlinearly algebraic equations leads to the numerical solution at each time step. At first, the behavior of failure is investigated for thin viscoelastic plate whose two opposite sides are free and other two sides are subjected to in-plane compression and hinged. The comparison with experimental results indicates that the method given in the paper is effective and produces satisfactory prediction for the critic time of failure that is defined by which the rapid increase of deflection occurs. It is shown that the accompanied creep damage deteriorates gradually the flexural rigidity and caused the rapid increase of deflection. At last of this part, the creep analysis of viscoelastic rectangular thin plates subjected to uniform transverse pressure and hinged at edges is conducted. Results show that the principal directions of stress and damage tensor can be considered time-independent during creep deformation of plates, and the deflection approaches to an asymptotic value due to the redistribution of stress when the pressures on plates lie in some extent, the isotropic damage model gives larger deformation than anisotropic damage model does, also, the coupling of tension-bending, which arises from the evolution of damage along thickness, increases the creep deflection and this effect becomes more remarkable if the loads get larger. When the uniform transverse pressures are large enough to cause failure, governing equations can not be simplified by ignoring stiffness B and derivative of stiffness parameters with respect of the spatial coordinates.3D finite element dynamic model for cable-stayed bridge is constructed based on Midas software. Towers,main beams and piers are modeled as spatial beam elements, and main beams and cables compose"fish bone"pattern. Cables are discretized as spatial truss elements considering the effect of drooping and then modifying stiffness. Firstly, analysis of structure dynamic characteristics is carried on, then using time history analysis, seismic response of cable-stayed bridge with and without viscoelastic dampers is compared under 100 years beyond probability 3% X + Zdirections earthquake excitation. The analysis results indicate that viscoelastic dampers can improve the earthquake resistance ability of the cable-stayed bridge. With the energy dissipation of viscoelastic dampers, the main beam of cable-stayed bridge has smaller seismic response displacements,accelerations and the seismic response of internal force of tower can be attenuated also. Meanwhile, the influence of viscoelastic dampers parameters on the earthquake resistance ability is investigated and a set of optimum parameters is suggested.