Study On Nonlinear Numerical Calculation Methods Of Pile Foundations Under Composite Load

In practice,pile foundations are usually employed to undertake vertical and lateral loads together,rarely by vertical or lateral loads alone,such as high-rise buildings,ports,bridges,offshore drilling platforms or high-rise tower construction and so on.It is complex to know the process of the loading transfer and failure mechanism of pile under composite load,which are influenced by many factors,and its force traits are also more complex than the pile under vertical or horizontal load alone.To reveal the deformation of the pile under combined load deeply,the following aspects were studied in the paper:(1)Based on the elastic foundation beam method and the principle of composite stiffness and bi-parameter,each infinitesimal segment of pile foundations with the composite loads was carried by the force balance analysis,and differential equations which focus on the P-?effect were established,considering the factors of the internal force and displacement such as the weight of pile,friction resistance,variable stiffness,variable cross-section.On this basis,three cases of the internal force calculation process of the pile foundations were discussed like no free length of the pile,the free length of the pile and pile column pier.Then finite difference method based on the pile foundation coefficient method was derived by using MATLAB software to write the corresponding program which was relied on examples for verification.It is showed that the compounds were accurate and reliable,and could be applied to calculate a bridge pile or high pile caps under the horizontal and vertical loads.(2)Combined with composite stiffness principle and bi-parameter method,the improved elastic link finite element method under composite loads considering P-? effect was proposed on ABAQUS platform,a large general-purpose finite element software.The elastic foundation beam model was built in the paper,on the basis of the actual project,and the results of finite difference method and link finite element method were compared with the site monitoring data to verify the accuracy of the two methods.It is worth noting that the result of shear force was smaller in the corresponding m finite element method,which will result in insufficient quantity of pile reinforcement stirrups and insecurity.In additions,for the small exposed section pile or low capping pile,the vertical and horizontal bending or P-A effect would not tend to perform obviously.(3)Based on the data of indoor model test,the mechanical deformation properties of pile foundations under composite loads on the level ground were studied which focused on the properties of the two pile foundations(rigid short pile and flexible long pile)for limit states.The three-dimensional finite element numerical simulation was used to analyze the responses of the two typical pile foundations by large-scale nonlinear finite element software ABAQUS.Meanwhile,the results of finite element method were verified and compared with the data of the laboratory test in order to obtain the distribution of internal forces and soil resistance of pile foundations under composite loads.(4)On the basis of indoor model test,the three-dimensional finite element numerical model of pile foundations on the slope under composite loads was established using the finite element software ABAQUS.The single and double row piles were respectively studied to obtain the distribution of internal forces and soil resistance of the two typical pile foundations,the slope deformation and the failure regularity.Finally,the multiple factors affecting the sensitivity of the double-row pile foundations on the slope were analyzed,such as row spacing,diameter,the stiffness of coupling beam,elastic modulus of soil,the free length and embedded depth of pile and other parameters,in order to provide some reference for the design and construction of the double-row piles on the slope.