| In this paper,based on the limit deformation criterion and hot spot stress method,the ultimate bearing capacity and fatigue performance of 12 T-type circular steel tubular joints under axial tension after corrosion are studied in the following aspects:(1)The corrosion of the specimens was carried out for 60 days and 120 days by neutral salt spray test in the laboratory.The variation of the surface morphology and the weight loss rate of the specimens with the corrosion time were obtained.The results show that the weight loss rate of the brace tube is higher than that of the chord tube in the same corrosion period,and the increasing speed of the weight loss rate slows down with the corrosion.Compared with the light corrosion,the density of corrosion pit is smaller,but its area and depth are larger,and its surface is more rough.(2)Three specimens with different corrosion degree were tested for ultimate bearing capacity in axial tension.The ultimate failure mode of the specimens is the yield failure of the upper surface of chord.Further study on the deformation curve of chord,the load-strain curve of joint area and the load-strain curve of joint shows that the ultimate bearing capacity of joint decreases gradually with the increase of corrosion degree,and the strain on the top surface of chord along the axis direction reaches yield faster.The strain of the branch pipe of the three specimens basically shows linear change without yielding,and the strain tends to decrease with the increase of corrosion degree.(3)The stress concentration and fatigue test of 9 specimens in three groups were studied.By extrapolation method,the measured value of the gradient strain is extrapolated,and the distribution rule of the hot spot stress concentration along the weld toe of the intersection line is obtained under different corrosion degree.The maximum value appears at the weld toe of the chord saddle,the maximum value of SCF of severe corrosion is greater than that of non corrosion,and the maximum value of SCF of non corrosion is greater than that of light corrosion.Combined with the experimental phenomena,the initiation and extention of fatigue crack are analyzed.The basic law of crack extention is summarized as three stages: rapid extention to stability,slow extention to through wall thickness,through wall thickness to fatigue failure.Then,according to the stiffness degradation curves of each specimen,two kinds of stiffness degradation modes are summarized.It is found that corrosion has an effect on fatigue crack growth and stiffness degradation.Based on the forced regression analysis of fatigue life data,the S-N curves of different corrosion degrees are preliminarily obtained,in which the S-N curves of severe corrosion are located on the other two S-N curves.Compared with the S-N curves recommended by different codes,the results of cidect are most close to the test results in this paper,but it is still too conservative to evaluate the fatigue life of severe corrosion.(4)The applicability of the finite element simulation is verified by comparing the simulation results of ABAQUS with the experimental results without corrosion.Finally,the finite element analysis of 24 groups of branch pipes under axial tension is carried out,and the influence of single parameter change on the ultimate bearing capacity and stress concentration distribution is studied.At the end of the paper,the author analyzes the deficiency of this research and the possible content of this topic.The paper has 81 diagrams,24 tables and 91 references. |
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