Fine Research On Mechanical Properties Of Junctional Pile Of Heavy-duty Construction Platform

Steel tubular piles can provide sufficient bearing capacity,easy to construct and dismantle,and can be reused,so they are often used as the substructure of construction platforms.The top of the steel pipe pile of the construction platform is connected with the main beam of the structure.In some positions,the horizontal and vertical arrangement of the main beam is changed.At this time,the steel pipe pile is the junction pier.There is non-center stress in the junction pier,and the common stress mechanism of pile-soil is complex,and there are many influencing factors.It is of great significance to study the mechanical properties of the junction pier for the safety and reliability of the construction platform structure.Therefore,based on the construction project of a bridge construction platform,this paper adopts the numerical simulation method to study the mechanical characteristics of the junction pier.The main research contents are listed as follows:Firstly,the load transfer mechanism of pile-soil system was introduced on the basis of referring to relevant literatures,and the dynamic change process of pile-soil interaction force transfer was elaborated in detail,which was described by mathematical expression.The theory of determining factors of ultimate bearing capacity of single pile is summarized,and the recommended algorithm of bearing capacity of pile foundation under lateral load and vertical load in the code is summarized.Secondly,the overall analysis model of the heavy-duty construction platform structure was established through Midas/Civil to obtain the stress and displacement of each component of the construction platform under different load combinations,and the safety judgment of the construction platform was made based on the rationality of the stress and displacement.It is found that the connection mode of pier top has little effect on the lateral and vertical displacements,and the transverse displacements decrease with the increase of pier top connection strength,which indicates that the strengthening of pier top connection has a certain limiting effect on the substructure displacement.Different pier top connection modes have little influence on axial force.When there is rigid connection at the pier top,the maximum bending moment increases greatly compared with the elastic connection.With the increase of pier top connection strength,the maximum shear force on pier top increases.Then,a fine stress analysis model of pile-soil interaction was established by ABAQUS to analyze the influence of different soil around the pile and different load types on the mechanical properties of the junction pier,and the distribution law of stress field of the junction pier under different loading states was obtained.Under the action of load,the maximum stress appears on one side of the pier roof under pressure.Below the mud surface line,the stress distribution decreases gradually with the deepening of the pier.When the pier is in different rock and soil bodies,the comprehensive physical and mechanical indexes of rock and soil bodies are better for the pier.The stress distribution of junction pier is obviously different with different load types on pier roof.The coupling action of bending moment and axial force on pier top is the most unfavorable to junction pier.When the coupling action of bending moment and axial force is applied to junction pier in practical engineering,corresponding measures should be taken to control it.Finally,by setting the control group with different parameters,the four factors that affect the mechanical properties of the junction pier,such as pile inclination,soil depth,wall thickness and transverse pile spacing,are compared and analyzed,and the stress and deformation of the junction pier under different conditions are obtained.By calculating the sensitivity coefficient,the absolute values of the average sensitivity coefficients of the four influencing factors were obtained as follows: 0.79,1.69,0.73 and 0.23.The results show that the penetration depth has the greatest influence and is the dominant factor affecting the ultimate bearing capacity of junction pier.