On the performance of monopile weldments under service loading conditions and fatigue damage prediction

Thick weldments used in offshore structures frequently act as fatigue crack initiation sites due to stress concentration at weld toe well residual fields. This paper investigates the cyclic deformation behavior of S355 G10+M steel, which is predominantly wind applications. Owing vast size difference monopile structure and cross-section, a global–local finite element (FE) method was used, geometry adopted from circumferential joints turbine foundations. Realistic service loads collected using supervisory control data acquisition (SCADA) wave buoy techniques were FE model. A nonlinear isotropic–kinematic hardening model calibrated strain controlled results obtained base metal (BM) cross-weld specimen tests. The tests revealed that BM (WM) undergo continuous relaxation. Fatigue damage over period 20 years operation predicted local root life limiting criterion. study helps quantifying level conservatism current design approaches has implications towards making energy more economic.