Internal Forces And Displacement Analysis Of A Single Pile Under Combined Action Of Harmonic Horizontal Load And Torsional Vibration

In recent years,the development and utilization of marine resources ha ve prompted the continuous construction and use of offshore wind turbines,offshore platforms,and offshore bridges.Pile foundations are widely used in these offshore projects because of their high bearing capacity,small deformation and good stability.However,in the complex and changeable marine environment,the pile foundation s are often subjected to horizontal eccentric dynamic loads caused by wind,waves,currents,and foreign object crash load.This horizontal eccentric dynamic load is divided into a combined action of horizontal dynamic load and torsional vibration,which has a great impact on the bearing capacity and deformation mechanism of the pile foundations.Thus,based on the existing research results,this paper conducted theoretical analysis and numerical simulati on research on the internal force and displacement of the single pile under the combined action of horizontal dynamic load-torsional vibration.The main works are as below:Firstly,for the torsional vibration(T(t))single pile in the uniform foundation,assumming that the soil around the pile is a homogeneous isotropic material and the pile shaft is a uniform linear elastic rod,the definite solution problem of the rock-embedded pile is derived in the cylindrical coordinate system under the action of harmonic torque on pile top.Using the boundary conditions of the pile-soil system,the analytical solution of the torsion angle and torque of the pile shaft is solved,and the variation rules of the pile top’s stiffness,pile shaft torsional angle and torque are analyzed.Secondly,based on the finite element method,the element stiffness matrix of a single pile in homogeneous foundation under the combined action of harmonic horizontal load-torque(H(t)-T)is established.By considering the stiffness contribution of the soil around the pile and the coupling effect of H(t)-T,a comprehensive stiffness matrix of the pile shaft is formed.The calculation program of the internal force and displacement of the pile shaft is compiled by MATLAB,and then the length-diameter ratio,pile-soil stiffness,dimensionless frequency and boundary conditions of the pile toe are discussed through parameter analys is to study the influence of these parameters on the internal force and displacement of pile shaft.Thirdly,based on the solution of a single pile under torsional vibration and combined action of H(t)-T,using the Winkler Foundation Beam Model to simulate the effect of the soil around the pile,and considering the additional stiffness of the horizontal reaction force,hoop friction and H(t)-T coupling effect,the comprehensive stiffness matrix of the pile in uniform foundation under combined action of horizontal dynamic load and torsional vibration(H(t)-T(t))is formed.Then,the MATLAB program is used to solve the internal force and displacement of the H(t)-T(t)loaded pile.The bearing deformation characteristics,and the effect of H(t)on the torsional complex stiffness of pile top and torsional angle and torque of pile shaft are discussed through parameter analysis.Finally,based on the ABAQUS platform,the 3D numerical analysis model of a single pile under H(t)-T(t)combined loads is established.The model is degraded into a single under horizontal dynamic load and torsional vibration load to verify the rationality of the model.Furthermore,the length-diameter ratio,the pile-soil stiffness ratio and boundary conditions of the pile toe are selected for parameter analysis to reserch the variation law of internal force and displacement of the pile under combined load is discussed.