| ABSTRACT:Bridge with pile foundations is an important component of linear traffic engineering, whose anti-seismic performance of has great influence on the safety operation of railway under strong earthquake. However, the earthquake damages of bridge structures designed by current seismic codes in bridge were very serious under some recent earthquakes. This phenomenon indicates that the seismic design theory and method of bridge used in present still need further research and development. At present, local topography effect, dynamic pile-soil interaction, multi-support excitation and frozen and thawed surface soil effect are need to consider when analysis the anti-seismic performance of grand bridge in cold area. Considering the physical and mechanical properties sensitivity of frozen soil, the further study on dynamic characters of pile in frozen soils becomes an indispensable content in analysis the seismic response of grand bridge engineering in cold region.In support of National Natural Science Foundation of China (90715013), the main studies in this dissertation are listed as follows:1. Direct shear test and static tri-axial and dynamic tri-axial compression tests of frozen sility soil were present, and the relationships of friction angle, cohesion, dynamic strength, dynamic elastic modulus, damping ratio and other physical quantities with temperature and moisture were studied. The test results can provid physical mechanics parameters of frozen sility caly for numerical calculations.2. A set of model experimental system for dynamic frozen soil-pile interaction was developed in this dissertation. Determination of performance parameters of dynamic loading system, design of model test chamber, analysis of refrigeration effect, design of loading frame and connection with experimental chamber were also introduced. The results of verification test show that the test system can supply frozen soil environment for experiments, can simulate and analyze the dynamic behaviors of frozen soil-pile preferably. Moreover, this system can be used in other researches on frozen soils.3. Based on the self-made model experimental system, experiments about dynamic property of model pile foundation under lateral dynamic loads in-5℃,-3℃and partially thawed permafrost were conducted. The displacement-force relationship of pile head, dynamic stiffness of pile foundation in horizontal direction and bending moment distribution of pile body in different permafrosts mentioned above were studied. At last, a dynamic BNWF model of dynamic frozen soil-pile interaction including separation effect and friction effect of pile and soil was proposed in this dissertation.4. A calculation model of dynamic pile-pier interaction system in permafrost considering the pile and soil material nonlinearities and contact effect between them was built, and the dynamic response of pier in different permafrost site under two earthquakes is studied.5. Based on the equivalent load method for earthquake input of the viscous-spring artificial boundary theory, numerical simulation of external source wave problem for obliquely incident transient plane SV wave was realized in ANSYS software. Seismic responses analysis of a typical valley site in cold region were carried out by method mentioned above. The results show that considering local topography effect, seismic incident angles, surface thaw soil thickness and seismic spectrum characteristics is very necessary.6. Nonlinear seismic response analysis models of a multi-span simply supported bridge and a rigid frame bridge were built, and effects of local topography effect, pile-soil dynamic interaction, seismic wave incident angle and the surface thawed soil thickness on the dynamic response of bridge structures were studied in this dissertation. The results show that the effects of topography and pile-soil dynamic interaction on seismic response of bridges have important influence than thawed soil thickness. |
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