Dynamic response of offshore jacket platform including foundation degradation under cyclic loadings

A 1/10 scale model is investigated to study the influence of the foundation degradation on the dynamic response of an offshore jacket platform. Experiments were conducted in multi-layer saturated soil under different water depth. A vibration exciter which amplitude and frequency could be changed was employed to simulate realistic loads. The model was scaled using dimensional analysis according to the artificial mass similarity principle and Buckingham π theorem. The horizontal dynamic response under the foundation degradation after varying cyclic loadings acted were studied. FE models were designed by means of the lumped parameter method or the equivalent pile technique to handle the pile-soil interaction in ABAQUS to analysis dynamic behavior of the jacket platform. Experimental results shows that the foundation degradation is related to the motion amplitude and the frequency of the piles. The degradation will result in the jacket natural frequency depressed, but it has little impact on the system damping. Comparison of the numerical and experimental results shows that applying the lumped parameter model with p-y curve PSI element to simulate soil-pile-upper structure interaction can obtain much higher accuracy than using the equivalent pile technique. Fair agreement between the experimental and theoretical results was obtained.