The calculating method of SCF for CFST K-joints with array-arranged internal studs

To study the stress concentration factor (SCF) in the concrete-filled steel tubular K-joints with array-arranged internal stud (CFST KSA-joint), the CFST KSA-joints full-size specimen tests were carried out, the accuracy of the solid finite element (FE) nonlinear analysis method was validated, the mechanism of the effect of internal stud on the SCF of CFST KSA-joints were revealed, the theory of equivalent wall thickness was established, a simplified curved beam with equivalent spring support was proposed, and the wall thickness correction coefficient was derived, a CFST KSA-joint SCF calculation method with high accuracy was developed. The key study findings indicate that the deployment of array-arranged internal studs can effectively mitigates stress concentration in concrete-filled steel tubular K-joints (CFST K-joints), resulting in an 88.7 % reduction in SCF. Comparison of FE and test results showed a maximum deviation of only 6.30 % in displacement and 5.14 % in hot-spot stress. Employing the CFST K-joints SCF calculation method to calculate the CFST KSA-joint SCF has an error of up to 42.3 %. Sensitivity analysis reveals that CFST KSA-joint chord wall thickness and inclined angle of the brace to the chord significantly influence SCF. Furthermore, a positive correlation was observed between stripping distance and hot-spot stress at the chord's tensile side. The SCF decreases with increasing stud diameter. Utilizing the equivalent wall thickness theory, the derived CFST KSA-joint SCF calculation method exhibits an error lower than 19.6 %, representing a 127 % improvement in accuracy compared to CFST K-joints SCF calculation methods that do not consider the stud.