Research On Single Pile Subjected To Torsion Based On Nonlinear Programming Method And Finite Element Analysis

With the rapid development of China's economy and the growing demand for transportation and energy,in recent years,large scale infrastructure construction such as overpasses,cross sea bridges,offshore platforms and wind power towers are expanding.Because of their high bearing capacity,small settlement,uniform stability,good applicability and convenient construction,the pile foundation is widely used in these structures.In the environmental stress complex,in addition to these structures by its own gravity and the upper load,is also affected by the wind load,wave load and high-speed vehicles and ships,so the pile foundation subjected to torsion force.If the design of the pile foundation in the actual engineering is not suitable for torsion or the neglect of such torque load,it will affect the safety and applicability of the foundation,and thus bring disastrous consequences.And,compared with other forms of load,torsion is more likely to lead to pile failure.So,it is very important to study the response characteristics of pile foundation under torsion load.Based on the previous research work and achievements,the calculation of internal forces and torsional deformations of single pile subjected to torque load is studied and analyzed.The main work is as follows:Firstly,in order to obtain the internal force and torsional deformation of single pile under the torque,using the nonlinear soil springs to simulate the interaction between the pile and soil,a simplified model for single pile is established,which can considerate the incoordination of deformation at the pile-soil interface.Afterwards,the total energy expression of the pile-soil system is obtained by discreting pile body into several units.And considering the force balance of pile body and torsional displacement continuity conditions,a nonlinear programming model of a single pile subjected to torsion is established based on the principle of minimum energy,which can be solved by the method of optimization to obtain the torsional deformation of single pile.Then,the torsion in the double foundation model in calculation and analysis,verify the applicability of the method in layered soils;a model test whose calculation program is compiled with MATLAB software is used to verify the present method by comparing the results of calculation with the experimental results.Secondly,a simplified calculation model of single pile subjected to horizontal force and torque is established by improving the calculation model based on the above research.Considering the pile displacement continuity conditions,a nonlinear programming model for calculating the deformation of a single pile subjected to horizontal force and torque is established based on the principle of minimum energy by dividing the pile into several elements,which can be solved by the optimal calculation method to obtain the deformation of single pile.And the feasibility of the method is verified by an example.Combined with an engineering example,the corresponding calculation program is compiled by MATLAB.On this basis,the influences of the factors such as the elastic modulus of the pile,the diameter of the pile and the ratio of length to diameter of the pile on the stress and deformation of the single pile subjected to horizontal force and torque are discussed.Finally,based on the ABAQUS finite element software,a numerical calculation model of single pile under torsion is established based on the prototype of a model test,which calculation results were compared with the results of model test to verify the correctness of the numerical calculation model.And the influence of the friction coefficient of the pile-soil interface on the torsional pile is analyzed to obtain the corresponding conclusions by changing the friction coefficient of the pile-soil interface in the model.