Dynamic Characteristics Analysis Of High Pier-Group Piles In Consideration Of The Pile-soil Interaction

With the implementation of Western Development Program in recent years. The infrastructure pace of highways and railways in remote western mountains become faster and faster. These bridges with high piers, as the key projects in main lines of communication on account of that span rivers, channels and valleys, are belonging to typical irregular girder bridge. Due to given service range, anti-seismic design codes at home and abroad are unavailable for these piers. Moreover, a large amount of theoretical analysis and test researches demonstrate that, the dynamic interaction of soil-foundation-high pier system has a great influence on the dynamic characteristics of superstructure, which may remarkably change its seismic response. Accordingly, the seismic design theory of irregular high piers is systematically studied to discover its dynamic interaction subjected to earthquake excitation in this dissertation.Firstly, with the summarization of lots of interrelated references, seismic design philosophy of high piers, seismic analysis of high piers, a state of the art survey of soil-structure interaction is presented, and the analytical methods of dynamic pile-soil-superstructure interaction are summarized. Base on considering of tapered pier behavior and the soil-pile interaction, bridge pier and group piles are simplified as global properties, and presents the analysis model of tapered pier supported by group piles. By using the southwell frequency composition method, analysis model is decomposed into two subsystems:elastic deformation of bridge pier and rigid deformation of group piles, then, the natural frequency of which are soluted by finite method and energy method. Further, the global natural frequency of tapered pier is deduced. Moreover, the comparison between calculated results and the real engineering examples shows that the method is reasonable, and the analysis results of the parameters of pier in natural frequency could be available for some reasonably conclusions.Secondly, in order to further study on dynamic response characterize of pile-high pier structural system, on the basis of analyzing dynamic pile-soil-superstructure interaction and nonlinear dynamic response of soil, the elastic-plastic constitutive relationship suitable for the pile-soil-high pier system was established. Furthermore, combining practical projects and with the aid of nonlinear finite element analysis software, the deep investigation of discontinuous deformation between pile and rock contact area, simulation of soil border, division of mesh size, and the structure damping were carried and a 3-D nonlinear finite element model of pile-soil-high pier interaction was established, fully taking into account the nonlinear soil materials and pile-soil contact.Furthermore, the viscoelastic border was realized by the APDL language in the program ANSYS, the time-viscoelastic artificial boundary was amended in the elastic-plastic analysis, and the variation law of the dynamic characteristics of the pile-soil-high pier system in different seismic loads was studied. Moreover, the influence of pier internal forces and deformation by the pile-soil-high pier interaction under seismic loading were analyzed, so the dynamic mechanism of pile-soil-high pier structural system is more profound understand.At last, the seismic responses influence of the pile-soil-high pier interaction system under the different stiffness of superstructure, different soil parameters, different combinations of soil layers, and interlayer were investigated, some reasonable conclusions for engineering anti-seismic design and operation were obtained.