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

为研究冰对厚冰环境下大型海洋结构物地震反应和抗滑动力稳定性的影响，提出了土-结构物-水-冰非线性相互作用系统的一般分析方法。在该方法中，一个简单的半无限元方法被新引入来表示半无限延伸的水系统。通过建立大坝-水-地基模型，验证了该方法的准确性，并采用二维有限元方法对土-结构-水-冰非线性相互作用系统进行了分析。在模型建立中，采用改进的节理单元模拟土与结构接触面的滑移现象，并通过比较虚拟水质量的影响，研究了作用在结构表面上的动水压力的影响。一般情况下，动水压力的精确估计得到的结构位移和速度响应比虚质量法小，而加速度响应比虚质量法大。通过对场地土的室内强度试验，考察了冰的各向异性对场地土强度的影响，结果表明冰的各向异性对场地土强度的影响很小。当冰变硬时，即温度很低时，这种影响不可忽略。

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.