初始裂缝对重力坝地震响应特性的影响
Influence of Initial Cracks on Seismic Response Characteristics of Gravity Dam

初始裂缝对重力坝抗震安全性的影响不可忽视，甚至成为控制结构安全储备和破坏模式的关键因素．将水平集方法应用到初始裂缝界面的描述及加强单元类型的判别，并与扩展有限元相结合，通过在相关节点的影响域上富集非连续位移模式，描述裂缝的扩展．基于扩展有限元算法研究了不同位置深度和倾角的初始裂缝对重力坝地震全过程中动力性态、最终破坏模式和缝面动力行为的影响．结果表明：坝顶水平向位移波动幅值、缝面的张合及最终滑移状态均随着初始裂缝深度的增大而增大；初始缝倾角并不作为坝体最终破坏模式的控制因素，坝体的最终破坏形态主要受坝体在地震作用中的应力场条件控制；倾斜向上初始缝一定程度上抑制了开裂路径的发展，对坝体的 地震危害最小．
As the main form of initial defects, the influence of cracks cannot be ignored specially, and even may become the critical factor of structure safety and its failure modes. The level set method is employed to describe the ini tial crack interface and judge the element types. Based on both extended finite element method (XFEM) and lever set method (LSM), it is carried out that the crack extension by enrichment of discontinuous displacement mode on the node domain. Moreover, the influence of initial cracks on the gravity dam is studied, including its position depth and dip angle. Then the effects of initial cracks are discussed which is on the crack propagation and seismic response of the concrete gravity dam during the whole process of earthquake. The results show that: the displacement amplitude of dam crest, the size of opening and closing of the cracks and the slippage, increase with the increase of initial crack depth; the controlling factor of dam final failure mode and ultimate failure pattern is not the dip angle of the initial cracks but the stress field condition; inhibiting effect on the crack propagation appears when the initial cracks have upward angle so that small earthquake hazards will be produced to the dam body