Study On Compressive Bearing Capacity Of Tubular T-Joints With Different Degrees Of Damage Reinforced By CFRP

With the development of the times,steel structures have been widely used in engineering construction,especially in large structures such as stadiums,bridges,exhibition halls and offshore platforms.In steel tube structure,since the hollow circular tube wall is thin,the radial rigidity is small,and the weld has a large stress concentration phenomenon,local buckling or yielding easily occurs near the weld on the surface of the tube,which leads to failure,so the tubular joint is the weak link of the steel tube structure.At present,the domestic and foreign commonly used reinforcement methods include stiffened internal ring reinforcement,internal plate reinforcement,local thickening reinforcement,plate reinforcement,collar plate reinforcement,etc.Among them,CFRP reinforcement method has no damage to the original structure and has no impact on the integrity of the original structure.At the same time,the bearing capacity of the structural material to be reinforced is hardly weakened.It has many advantages,such as convenient construction,light weight,high strength and corrosion resistance.It has been widely used in practical projects.In order to study the reinforcement effect of CFRP on T-joints with different damage degree,ABAQUS software is used as the research tool to study the failure mode and bearing capacity of T-joints with different damage degree strengthened by CFRP through establishing reasonable finite element model.The effects of damage degree,the thickness of the chord wall,the thickness of the CFRP,the wrapping method,and the modulus of elasticity on the bearing capacity of T-joints under compression are discussed.The main work and conclusions of this paper are as follows:(1)According to the test in the existing literature,by using the B-W damage criterion to simulate the damage,the numerical calculation results are compared with the experimental results of tubular joints reinforced by CFRP.It is found that the maximum error of the peak load and the peak load obtained by the test is 5.39%.It is proved that the B-W damage criterion can be used to analyze the damage of tubular joints.The rationality of the finite element method is proved.(2)Through the method of numerical analysis,the influence of geometric parameters(thickness ratio diameter ratio of chord and branch)on the ultimate bearing capacity of T-joints reinforced by CFRP with different damage degree is discussed,such as the wrapping method,thickness and elastic modulus on the bearing capacity of the joint.The results show that the greater the wall thickness and diameter of the chord,the ultimate bearing capacity of the T-joints reinforced by CFRP is greater under the same damage degree;the greater the thickness and elastic modulus of CFRP,the better the reinforcement effect;the best reinforcement effect of CFRP winding mode is 0 °/90°,under the same conditions.(3)By selecting 10 observation points in the finite element model and extracting the equivale plastic strain of the measurement points,it is found that under the same size of tubular T-joints,the greater the pre-damage degree,the greater the equivalent plastic strain,the lower the peak load.In the plastic hinge region,the farther away from the branch pipe,the smaller the equivalent plastic strain value of the chord.It can be predicted that the failure location of the specimen is at the location where the equivalent plastic strain changes greatly.(4)Based on the analysis of the results and the calculation theory of tubular joints at home and abroad,the calculation formula of bearing capacity of tubular T-joints reinforced with CFRP under damaged and undamaged conditions is modified,and the formulas for calculating the bearing capacity are compared with the experimental results,which verifies the accuracy of the calculation formula of bearing capacity.