Research On Seismic Design Method Of Pile Foundation For Railway Bridges

Gravity type piers with larger section and lower reinforcement ratio are widely used inChina’s railway bridges. In view of structural and mechanical characteristics of gravity typepier and focusing on the current main problems in seismic design, research on seismicresponse characteristics of pile foundation used in railway bridges is thoroughly performed byusing the combination of experimental study, numerical simulation and theoretical analysis.Performance-based seismic design method of the pile foundation is put forward. The mainresearch contents are as follows：(1)After reading a lot of literatures, present research situation of soil-pile-structureinteraction, seismic static and dynamic analysis model and seismic test on bridge pilefoundations are systematically summarized.(2)Taking gravity type bridge pier with common spans as research object, failurepatterns, production mechanism of plastic hinges, bearing capacity, skelon curve, hystereticlaws and energy dissipation capacity under low-cycle reversed loading are studied by usingquasi-static test on indoor reduced-scale pile foundation model.(3)On the basis of experimental study, a nonlinear static calculation model of group pilefoundations under horizontal load is put forward. Simulation method on elasto-plastic of pileshafts under variable axial loads is discussed. Modeling method of subgrade resistance isproposed, which should simultaneously consider horizontal resistance at lateral of pile shaft,vertical frictional resistance around piles shaft and vertical bearing resistance at pile tip.Constitutive relation of subgrade resistance and parameter value is given based on the code ofAmerican API. The rationality of analysis model is proved by model pile experiments.(4)Based on the nonlinear static calculation model of group pile foundations, the maininfluence parameters on nonlinear performance of pile foundations are analyzed. Influencelaw of these parameters on bearing capacity, displacement ductility of pile foundations andproduction mechanism, development process of plastic hinge of piles is summarized.(5) In order to control seismic performance of pile foundations, seismic design methodon the basis of two indexes is proposed which is damage level of pile member and structuralintegeral displacement ductility level. Modeling method of inelastic demand spectrumconsidering three kinds of soil-pile interaction effect and solution method of performancepoint on capacity spectrum method is given. A seismic simplified method of pile foundationsis put forward and the validity is proved by using application examples.(6)Dynamic nonlinear analysis model of group pile foundations is proposed consideringthe effects of separation and gap producing from the interface between pile and soil.Modeling method of dynamic constitutive relation on subsoil resistance considering above influencing factors is discussed and influence law of foundation nonlinearity on seismicresponse of pier and pile shaft is summarized. A nonlinear centralized supporting springmodel is put forward and proved by application examples.