Experimental Study On The Design Reliability Of Compressed Bearing Capacity Of Single Pile

This paper analyzes the failure characteristics,ultimate bearing capacity and load-displacement relationship of pile foundation under pressure by testing the axial compression and eccentric compression tests of the 48-section circular cast-in-place concrete piles.The reliability of the bearing capacity of cast-in-place piles was analyzed using the reliability method.The experiment was simulated using ABAQUS finite element method,and the numerical analysis results were compared with the experimental results.The factors that were not designed in the experiment were considered.(1)Analyze the influence of reinforcement ratio and compression method of longitudinal reinforcement on the bearing capacity of foundation pile.The test results show that the bearing capacity of reinforced concrete member is not a simple superposition of the bearing capacity of concrete and longitudinal reinforcement,and stirrup and longitudinal reinforcement.The reinforcement cage formed by the ribs has a restraining effect on the concrete,and can increase the bearing capacity of the test piece to some extent.In this test,the bearing capacity of the components was increased by 9%to 12%due to the restraint effect of the stirrups.The average bearing capacity of the biasing members(0,0.4%,0.8%,and 1.2%)with different reinforcement ratios(0,0.4%,0.8%,and 1.2%)is lower than that of the axial members with the same reinforcement ratio,and the bearing capacity is reduced by about 2.8%to 3.9%.(2)According to the calculation formula for the bearing capacity of foundation piles of the“Code for Design of Building Foundations”GB 50007-2011,the working condition coefficient?_c is taken as 0.91,0.93 and 0.95 respectively to design the reinforcements with the primary,secondary and tertiary safety grades.When the bearing capacity of the pile is calculated,the reliability indexes calculated are 4.2,3.7 and 3.2,respectively,which meet the requirements of the reliability indexes of the first,second and third levels respectively.Under the action of eccentric load,the reliability index of the specimen is lower than the reliability index under the axial load.The reliability index increases as the reinforcement ratio increases.According to the calculation formula for the pile bearing capacity of the"Technical Code for Building Pile Foundation"JGJ 94-2008,the reinforcement piles of the first,second and third grades are designed with 0.8,0.83 and 0.84 of the pile technology coefficient?_c.When the pile bearing capacity,calculated reliability indicators were 4.2,3.7 and 3.2,respectively,to meet the safety level of the primary,secondary and tertiary reliability indicators.It is suggested that when calculating the bearing capacity of reinforced piles according to“Code for Design of Building Foundations”GB 50007-2011,the working condition coefficient?_c can be taken as 0.6 to 0.91according to the engineering conditions;and it can be calculated according to"Technical Code for Building Pile Foundation"JGJ 94-2008..When the bearing capacity of the reinforced pile piles,the pile forming process coefficient?_c can be taken as 0.6 to 0.8 according to the engineering conditions.(3)Establish a comparison between the finite element model and the test results.The error between the compressive bearing capacity of the numerical analysis and the compression bearing capacity of the test is within 5%.Through the analysis of the factors affecting the compressive bearing capacity of the specimen,such as the concrete strength grade,reinforcement ratio,stirrup spacing,and eccentricity,the following conclusions were obtained:As the reinforcement ratio increases,the compressive bearing capacity of the specimen also increases.With the increase,the two have basically increased in equal magnitude.With the increase of the spacing between stirrups,the bearing capacity of the specimen decreases slightly,The distance between stirrups increased from 50mm to 200mm,and the compressive load capacity decreased by approximately3%.indicating that stirrups are also one of the factors that affect the compressive bearing capacity of the specimen.There is a positive correlation between the compressive bearing capacity of the pile and the strength grade of the concrete.Eccentricity is one of the important factors affecting the compression bearing capacity of the test piece.As the eccentricity increases,the bearing capacity under pressure decreases.When the eccentricity reaches about 1/4 of the diameter of the pile,the test piece is subject to The compressive bearing capacity is about 28%lower than the axial compressive bearing capacity,and its influence cannot be ignored in the actual engineering design.