Residual bearing capacity of concrete-filled double-skin steel tube K-joints after lateral impact

Abstract

With the application of jacket offshore wind turbines (OWT), the jackets are exposed to the risk of ship collision. However, concrete-filled double-skin steel tube K-joints (CFDST-K joints) in the jacket can still operate normally after slight impacts. To study the residual axial properties of the joints, eight CFDST-K joints and one hollow K-joint were tested by a long column testing machine, focusing on the failure mode, residual bearing capacity, displacement, and ductility after impact. Results indicated that the typical failure mode of the joints was characterized by overall bending resulting from excessive midspan deflection. The residual properties were negatively correlated with the initial damage. Specifically, the stiffness degradation was worsened as the impact energy and axial compression ratio increased, causing an evident decrease in residual bearing capacity and ductility. Moreover, increasing the outer tube thickness improved the bearing capacity by enhancing the confinement effect of the steel tube on the concrete. Furthermore, the hollow ratio exerted a great effect on ductility. A calculation method for the original loading capacity of CFDST-K joints was also proposed, and the damage index was introduced to assess the damage degree. The results verified that the joints still possessed excellent bearing capacity after impact.