Dynamic Analysis Of Offshore Structures Under Impact Load Using Interface Finite Element Method

Abstract

The main object of this paper is to fit with high degree of accuracy the true structure response by considering the concept of interface element which is used to simulate three dimensional soil-structure interaction in the dynamic analysis, therefore the dolphin of khor Al-Amaya berth no. 8 is analyzed as a case study. The (p-y), (t-z), and (q-z) curves which are adopted by American Petroleum Institute (API) are used to find normal and tangential interface moduli and end bearing modulus. For this purpose, a computer Fortran program Offshore_Inter has been built to obtain the required solution. The subspace iteration method is used to find the free vibration solution while Newton-Raphson modified method combined with Newmark's method is applied to get the nonlinear forced vibration solution. For both solutions, the conjugate gradient algorithm is used as a solver of the dynamic problem. A parametric study has been carried out including different soil type, soil engineering properties, loading time effect and the results are given in tables and graphs. The dynamic structural response is compared with the results of previous studies on the same structure and with elastic and Reese solution to show the difference between the different formulations. From obtained results, it is shown the interface solution increases the structure response by more than 80% comparing with Winkler method based on same curves mentioned above. Pile deflection and bending moment values along pile length are relatively increased many times than the solution obtained from elasticity theory and Reese solution. Finally, the increased soil strength will largely degrease the structure response for all soils.