Fatigue Performance and SCF Calculation Method of CFST K-Joints with Array-Arranged and Circular-Arranged Internal Studs

Abstract

To reveal the mechanism by which internal studs enhance the fatigue resistance of concrete-filled steel tubular K-joints (CFST K-joints) and to develop a method for calculating the stress concentration factor (SCF) of CFST K-joints with internal studs (CFST KS-joints), this study conducted full-scale specimen fatigue tests on CFST K-joints with array-arranged and circular-arranged internal studs. The influence of internal studs on the fatigue performance of CFST K-joints was thoroughly analyzed. The equivalent wall thickness theory was introduced, and the wall thickness correction factor was derived. A highly accurate SCF calculation method for CFST KS-joints was established. The research results indicate that the arrangement of internal studs can enhance fatigue life by 100.6% and reduce the SCF by 77.6%. Furthermore, the efficiency of circular-arranged studs is approximately twice that of array-arranged studs. When the undetermined factors mc for CFST K-joints with array-arranged and circular-arranged internal studs are set to 0.002 and 0.019, respectively, the maximum deviations of the wall thickness correction factor a are only 7.98% and 8.20%, respectively. Utilizing the equivalent wall thickness theory, SCF calculation methods for CFST K-joints with array-arranged and circular-arranged internal studs are derived, yielding errors of less than 19.6% and 21.4%, respectively.