Mechanical Performance Analysis of Concrete Filled Steel Tubular K-joints Subjected to Random Local Corrosion

Concrete filled steel tube(CFST) composite truss structures have superior structural performance and economic advantages due to the clear force transmission and excellent integrity. These structures have been widely used in large-scale infrastructures that serve in corrosive environments, such as cross-sea bridges, coastal towers, and offshore platforms. In such structures, the main bearing members and key connecting joints are affected by corrosion and sustained loads, which is a severe challenge to the safety and reliability of the structure. In practice, randomly distributed local corrosion normally occurs on the surface of steel. Due to the limitations of test facilities and numerical simulation technology, the research on CFST K-joints with random local corrosion is still limited, which restricts the understanding of the life-cycle performance and the establishment of scientific design methods for those structures. Thus, this paper aims to study the full-range performance of CFST K-joints subjected to random local corrosion and sustained load.
A detailed finite element analysis(FEA) modelling was presented to study the performance of CFST K-joints under random local corrosion and sustained load, which could take the random local corrosion of the outer steel tube and the complex time-dependent effects of the nonlinear material confinement into consideration. Based on the distribution trend of random local corrosion for steel structure in actual ocean environment, the simulation of random local corrosion on the surface of chord and brace was realized by combining Python and ABAQUS simulations, which can generate random pit distribution, identify corrosion elements and automatically mesh on the pitting corrosion area. In addition, the long-term characteristics of the core concrete and the time-dependent deterioration of nonlinear steel-concrete composite action are considered in the model. The established model was validated against reported test data and then used for further analysis, including the possible failure modes, the full-range load-deformation relationships, the residual ultimate strength, and the influence law of important parameters such as corrosion type(uniform distribution or random local distribution), volume loss rate, etc. The key parameters affecting the performance of CFST K-joints with random local corrosion were systematically evaluated, including the volume loss rate, the material properties, the diameter-ratio between chord and brace, the chord member diameter-thickness ratio, etc. Finally, simplified calculation methods for the residual strength of CFST K-joints were proposed based on parametric analysis. The accuracy of the formula was verified by the finite element results.
The results show that the failure mode of CFST K-joints with random local corrosion is mainly the local buckling of the compression brace, while the stress concentration tends to occur in the pitting corrosion concentrated area that leads to the local buckling failure. Due to the concrete infill in the chord, the mechanical performance of the joints is improved. Compared with uniform corrosion, local corrosion has a more significant effect on the performance of CFST K-joints while the random distribution of local corrosion further reduces the bearing capacity of CFST K-joints. When the volume loss rate remains constant, the ultimate joint capacity with random local corrosion is found about 13.2% lower than that with uniform corrosion; the volume loss rate of brace controls the ultimate strength of CFST K-joints.