Fatigue design of concrete-filled steel tubular T- and K-joints

Abstract

Steel tubular members are widely used in offshore structures and in infrastructure entities such as oil platforms and bridges. The tubular members are exposed to repetitive loading from sea waves, wind and traffic. Repetitive loading causes deterioration of the structural members through crack initiation and propagation which is called 'fatigue'. Fatigue strength has always taken most attention in the design of steel tubular members. Due to geometric discontinuity at the connected steel tubular members, high stress concentration exists at the joint. The location of high stresses is usually the location of fatigue crack initiation. In the last century, a large amount of research was conducted on empty (non-filled) steel tubular joints which resulted in the development of various fatigue design guidelines. At the beginning of the current century, researchers have effectively used concrete filled steel tubes to reduce stress concentration at the joint. With regard to the fatigue strength of welded steel tubular joints, there is still lack of understanding and further research is required. In this study, a comprehensive study, which covers experimental and numerical analysis, on the fatigue performance of CHS-to-CFCHS T- and K-joints based on the hot spot stress method has been conducted. In the experimental program, three CHS-to-CFCHS T-joints have been tested experimentally under axial tension, axial compression, in-plane bending and out-of-plane bending in the brace. SCF measurements in the three specimens under the three loading formats have been performed and compared with those for empty T-joints. Additionally, a CHS-to-CFCHS K-joint specimen was tested under balanced axial loading. SCF measurements around the brace-chord intersection have been performed. The experimental program was followed by an extensive numerical analysis study. A large number of finite element CHS-to-CFCHS T- and K-joints models were developed. The effect of the joint geometric parameters on the maximum SCF in CHS-to-CFCHS T- and K-joints has been studied and compared with those for empty T- and K-joints. Parametric equations for predicting the maximum SCF in CHS-to-CFCHS T-joints under the three basic loading formats and in CHS-to-CFCHS K-joints under balanced axial loading have been derived.

Date of Award	2019
Original language	English