Pier Analysis Of Dynamic Characteristics And Dynamic Identification Method Of Foundation Restraint Stiffness

The stiffness parameter identification of piers is more complicated than that of substructures or other structures. And it is difficult to control its construction quality and diagnose its defects. Based on the idea of system engineering,the foundation and the soil can be working together as a system,and the export of the system is the constraint stiffness of the foundation to the piers. Based on the combination of Rayleigh and Southwell's methods,the relationship between the compound fundamental frequency and the constraint stiffness of piers with different kinds of foundation changed with counterweights on piers'top is obtained. The frequency will be displayed by the relevant parameters of the piers. The fundamental frequency of the piers is decomposed to the sum of frequency of each subsystem consisted in inertia component and deformatable component. The inertia component includes distributed mass of piers,concentrated mass on its top and the foundation mass while deformation component includes deformation of foundation,flexural deformation and shear deformation. The influence of the factors on the fundamental frequency such as counterweight on pier top,constraint stiffness,non-uniform section factor,inertia moment of the foundation,shear deformation and stiffness of bent beam is expored where the finite element analysis is used to verify the accuracy of the modal. The results show that the calculation formula presented in this paper is simple in computation,high in precision and can meet the need of the engineering.Based on the dynamic analysis of the piers,a method is putforward to estimate preliminarily the lowest of foundation restraints stiffness and the relationship of translational restraint and rotational restraints. Based on the above theories,a dynamic analysis method of stiffness identify of piers is build. The relationship between fundamental frequency of the piers and its foundation stiffness is used to identify the foundation restraints stiffness by measuring different kinds of fundamental frequencies changed with counterweights on piers' tops. The simultaneous equations to identify the translational restraint stiffness and rotational restraint stiffness are established, then the construction quality of the piers and its foundation can be detected and evalued.