A simplified computational method for random seismic responses of a jacket platform

• The simplified method in this paper can truly reflect the platform natural characteristics.
• The method can calculate random responses directly avoiding the calculation of normal modes.
• This method can be applied to the problems of ocean engineering.

A simplified method for modeling Jacket Offshore Platform was developed and numerical examples were presented to demonstrate the validity of the proposed method. In this method, a jacket platform was described as a cantilever beam subjected to an axial compressive load acting at the top-end centre of the jacket. The random seismic responses of the model were derived by using both the pseudo-excitation method and the classical Ritz method. The authors found and demonstrated in this paper that this proposed method may be used to calculate the random responses accurately and efficiently. In particular, the responses of a non-uniform beam, in the form of an auto-PSD function, cross-PSD or higher spectral moments could be solved directly without the need to determine the normal modes. The writers included an example in which the solution was obtained using the proposed method with a selected Ritz function. The results were compared with that obtained using the conventional finite element method (FEM). The findings of the study showed that the proposed method was effective, practical and useful in the seismic design of platforms.