Research On Simplified Algorithm For Overall Seismic Performance Analysis Of Rigid Pile Composite Foundation-Foundation-Upper Structure

Rigid pile composite foundation is a new type of foundation treatment built at the beginning of 20 th century,it can make sure the pile and soil bear the load of upper structure together,thus,it can maximize the bearing capacity of soil and piles,reduce the foundation settlement;Rigid pile composite foundation has features of construction simple and quickly,saving construction cost,etc,having a widespread application in the high-rise building now.However,comparing to the actual project requirements,theoretical research cannot meet the practical needs,especially the research in terms of aseismic design of rigid pile composite foundation are scare.In the design of the superstructure,often ignore the impact of the earthquake on the composite foundation,which may make the upper structure have a safety hazard.The study of overall seismic performance analysis of rigid pile composite foundation-upper structure mainly focuses on model test and finite element numerical simulation.Model test need to do large scale test which requires a lot of mampower,time and money,however,numerical simulation is difficult for building model and actual engineering design.In this paper based on the above issues,a simplified algorithm for the overall seismic performance of rigid pile composite foundation-foundation-superstructure is established by theoretical deduction.This simplified algorithm can greatly simplify the difficulty of seismic analysis of the whole structure,if this simplified algorithm can be widely used in the daily design of the structure,which can reduce the difficulty of the design work to improve their work efficiency.In this paper,the research contents mainly focus on the following several aspects:(1)The whole simplified model of single pile composite foundation-foundation-superstructure is established,and the dynamic differential equation of each part is deduced.Then,according to the boundary conditions of the whole model and the interaction conditions of each part,the appropriate differential scheme is constructed to solve the dynamic differential equation of each part,finally the displacement response of each part under the earthquake action is obtained.(2)Programming the calculation process of overall seismic performance analysis of single pile composite foundation-foundation-upper structure by matlab software,calculation and analysis the response of the single pile composite foundationfoundation-superstructure,and calculation results are compared with others' research results to verify the feasibility of the simplified algorithm in this paper.Then,according to the principle of merging piles,the composite foundation of pile group is combined into single pile composite foundation,and building a simplified algorithm of rigid pile composite foundation-foundation-superstructure is established.(3)Select the appropriate seismic waves to research the seismic performance response of rigid pile composite foundation-foundation-superstructure,and the dynamic response of each part under the influence of frequent and rare earthquakes is analyzed,by comparing the results,it shows that the damping effect of the composite foundation is not obvious under the frequent earthquake,the result of calculation the upper structure is not different with that of the upper structure without considering the composite foundation,the damping effect of the composite foundation is obvious under the rare earthquake,the result of calculation the upper structure is very different with that of the upper structure without considering the composite foundation.(4)Finally,research that the mattress layer modulus and thickness,rigid pile diameter,pile length,impact on the seismic performance of the whole model.Through analysis,it finds that mattress layer thickness change has a little influence on the dynamic response of the model,both increasing the pile top and pile bottom shear force and bending moment of pile body by increasing the mattress layer modulus,which has adverse effects on the pile body;when cushion modulus increase,the maximum displacement of the upper floors and maximum displacement between layers of the upper floors are larger changes.The bigger the pile diameter,the shorter the pile,the greater the displacement of the upper structure,pile bending moment and shear force are larger.