Buckling Stability Analysis Of Pile Based On Statistical Damage Theory

Pile foundations with elevated caps have been widely used in highway and railway bridge projects with the further development of China’s infrastructure construction in mountainous areas and deep-sea.In mountainous areas and deep-sea,the buckling stability of piles is still a lack of in-depth study due to the constraints of topography,geological conditions,load level and construction conditions,which will greatly affect the economy,durability and safety of bridge engineering.Therefore,it is necessary to study more of the buckling stability mechanism of pile foundation from the bearing mechanism,failure mode and other aspectsThe experiments show that buckling failure is most likely to occur when the free length is large for pile foundations with elevated caps,especially in weak or liquefiable soil layers.However,the strength of pile material under long-term load is a dynamic process,which can be called "damage",and the characteristics are mainly manifested in the initial defect of pile shaft and the strength degradation under the load.At present,the buckling stability analysis method based on energy method has not sufficiently considered this,and it is hard to meet the increasing requirements of bridge construction in mountainous areas.Based on the buckling instability theory and the statistical damage theory,this thesis considers the damage of the concrete material of the pile shaft under load and attempts to find a set of buckling stability analysis method considering the damage of the pile shaft.The main work listed as following:(1)A comprehensive analysis of the bearing mechanism and failure mode of pile foundation have been made.After that,this paper summarizes the current research progress on buckling instability of foundation piles at home and abroad and discusses the current analysis methods for buckling instability of foundation piles.(2)Discussing the damage mechanism of concrete briefly,optimizing the damage factor of concrete based on the statistical damage theory in the damage evolution method,and propose a damage factor applicable to the foundation pile.(3)Comprehensive bearing mechanism of pile and pile body damage in the process of loading,considering the nonlinear characteristics of pile buckling process,the cusp mutation theory is introduced to select the appropriate pile deflection function,establish the cusp catastrophic model of bridge pile structure system.To solve the instability condition of structure system,which determine considering pile body damage of pile buckling instability critical load calculation method.On this basis,the influence of damage factor coefficient,pile top constraint condition,soil properties,pile body size and other factors on the critical load of buckling instability of foundation pile is discussed,this method works well when the embedding ratio is under 0.6.(4)In order to further explore the bearing mechanism and mechanical characteristics of the bridge foundation pile structure system considering pile damage,a three-dimensional finite element model of the bridge foundation pile structure system is established by using ABAQUS’ concrete damage plastic model in the finite element analysis.It is compared with the theoretical solutions,and the mechanical characteristics of the foundation pile structure system under different boundary conditions and material mechanical properties are analyzed.(5)The applicability of the theoretical method of this thesis in practical engineering is discussed with an example of a bridge project in the province.