中文摘要：

采用改进的扩展有限元法（Extended Finite Element Method，XFEM），即引入虚结点的XFEM，在静力功能基础上实现了动力断裂分析功能，并用于强震中结构多条裂缝的同时扩展分析。采用混凝土Ⅰ型和Ⅰ-Ⅱ混合型动力断裂试验进行了精度验证，然后将该方法应用于Koyna坝的地震开裂分析。结果表明，这一方法在求解混凝土Ⅰ型和Ⅰ-Ⅱ混合型动力断裂问题方面具有良好精度，其避免了网格不断重剖分的问题，也无需采用开裂单元的子域积分来描述非连续位移场，即可实现单元内连续断裂过程的模拟。

英文摘要：

An improved Extended Finite Element Method namely phantom node XFEM, is introduced to analyze the dynamic fracture process of multiple cracks in gravity dams subjected to strong earthquake. Experiments of dynamic fracture of mode I and mixed-mode Ⅰ- Ⅱ for concrete are used for accuracy verification. On this basis the seismic fracture of the Koyna Gravity Dam is analyzed using the proposed procedure. The results demonstrate that the improved dynamic XFEM has sufficient accuracy for analysis of concrete. It is also found that the simulation of progressive fracture process using this method can be carried out without using remeshing scheme, and it is not necessary to use subdomain integration to describe dis- continuities.