Study on hot spot stress distribution and fatigue life assessment of KK-type cast steel nodes based on scaled model test

Abstract

The use of cast steel nodes (CSN) in marine structures reduces weld concentration and optimizes structural design. However, these nodes are subjected to cyclic loading, which poses significant fatigue risks. This study investigates the fatigue life of KK-type CSN under cyclic loading to enhance their application by refining spatial CSN calculation methods. Firstly, the extrapolation points of hot spot stress (HSS) in the girth butt weld of CSN are identified, and the effects of varying slopes and reduction thicknesses on the stress concentration factor (SCF) of the weld are analyzed. The weld configuration utilized in finite element (FE) simulations and fatigue tests is established. Subsequently, a regression equation for calculating the SCF of CSNs is developed by identifying the key geometric parameters influence the SCF of the welds. The HSS for each weld in the tested CSN are then calculated, identifying the vulnerable regions prone to fatigue failure. The proposed regression equations are validated by comparing FE results with fatigue test outcomes. Finally, the fatigue life of CSN is compared to that of welded tubular nodes (WTN) under identical conditions, demonstrating that the use of CSN can improve the overall fatigue performance of jacket structures.