THE EFFECT OF ICE ON THE SEISMIC RESPONSE AND DYNAMIC STABILITY AGAINST SLIDING OF OFF-SHORE STRUCTURES

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The purpose of this study is to investigate the effect of ice on the seismic response and dynamic stability against sliding of a large scale off-shore structure that is surrounded by thick ice.The general method for analyzing the nonlinear soil-structure-water-ice interaction system was proposed first. In the method, a simple semi-infinite element method is newly introduced to express the semi-infinitely extending water system. The accuracy of the method was demonstrated by using dam-water-foundation models.Then the nonlinear soil-structure-water-ice interaction system was analyzed by the two dimensional finite element method. In modeling the system, modified joint elements were used to simulate sliding phenomena at the interface between the soil and the structure base.The effect of the hydrodynamic pressure acting on the structural surface was examined by comparing the effect of virtual mass of water. Generally, the exact estimation of the hydrodynamic pressure gave the smaller response of displacements and velocities of the structure but larger accelerations than those obtained from the virtual mass method.The effect of the material nonlinearity of soil was examined. The effect was very small when the soil strength which was obtained from the laboratory test of the soil of the site.The effect of anisotropy of ice was also examined. The effect was not negligible when the ice becomes hard, i.e. the temperature was very low.