Radial temperature difference action model of concrete-filled steel tube in natural environments

To propose a temperature action model for calculating the interface stress of concrete-filled steel tube (CFST) in natural environments, four CFST components with different orientations and inclinations were fabricated for temperature field tests. Based on the measured data, a refined finite element model (FEM) was established for the numerical calculation of the temperature field. The radial temperature difference distribution and variation in different directions were analyzed using the measured data, and the radial distribution and circumferential distribution of radial temperature difference were fitted by the finite element calculation results and measured data. Finally, a comparison was made on the temperature deformation and stress calculated by the three-dimensional temperature field, radial temperature difference action model, and vertical temperature gradient model in the specification. Research results show that the radial and circumferential distributions of the radial temperature difference exhibit significant nonlinear distribution characteristics. The radial positive temperature difference is mainly influenced by solar radiation intensity, while the radial negative temperature difference is related to abrupt changes in air temperature. The measured maximum radial positive temperature difference can reach 23.16 ℃, and the minimum radial negative temperature difference is -10.43 ℃. The radial positive temperature difference can be described by the product of the radial power function and an improved one-dimensional Gaussian distribution in the circumferential direction, while the distribution of radial negative temperature difference can be characterized by the product of the radial power function and the minimum radial temperature difference. The proposed radial temperature difference action model is more precise than the vertical temperature gradient in the specification in the calculation of temperature effects in CFST, especially in the interface temperature stress. The maximum normal stress at the interface can reach 0.79 MPa under temperature action, which may lead to debonding or void of the steel-concrete interface. The proposed radial temperature difference action model can accurately assess the adverse effects of temperature, which provides support for the design of CFST interfaces.