混凝土大坝的抗震安全评价

本文论证了混凝土大坝重点是高拱坝的抗震安全评价的实践与发展现状。现有的评价准则主要依据混凝土的强度，特别是抗拉强度来判断大坝的安全性。大坝的应力计算则以弹性动力分析为基础。各国规范关于地震设防水平和大坝的容许拉应力数值有很大差别，表明认识上的不一致。事实上，由于各坝坝高、坝型、地形、地质条件不同，地震时坝身中某一部分产生的最大拉应力不足以全面反映大坝的抗震安全性。混凝土的动态强度是大坝抗震安全评价中的一个薄弱环节。大坝抗震设计中目前只依据Raphael进行的局部加载速率的试验结果选取混凝土的动强度。实际上，地震作用下，不同的坝不同部位的应变速率是不相同的，而且混凝土的动强度还和应变历史、初始静抗压强度、含水量以及尺寸效应等许多因素有关，有待作深入研究。在以上分析基础上，文中建议了混凝土大坝抗震安全评价的合理方法以及进一步的研究方向。

Seismic safety evaluation of large concrete dams

The current practices and state-of-the-art of earthquake safety evaluation for large concrete dams with emphasis on high arch dams are reviewed. It is pointed out that the existing assessment criteria are based on the dynamic strength, especially the tensile strength of mass concrete, and linear-elastic dynamic analysis methods are used for the evaluation of earthquake stress response. However, the adopted design levels of earthquake ground motion and allowable tensile strength in different countries are diversified. In fact, every arch dam possesses its specific features and the maximum dynamic tensile stresses at some positions of the dam according to the linear-elastic response analyses is insufficient for the assessment of earthquake safety of the dam. The current criterion of concrete tensile strength is based on the limited experimental results obtained by Raphael for core specimens from five dams at a strain rate corresponding to 5Hz. Whereas, the dynamic forces at different parts in different dams will be generated with different strain rates during earthquake. In addition, the dynamic strength of mass concrete are affected also by various factors such as the loading history, the static compressive strength, the water content as well as the size effect. In this paper, the appropriate seismic safety assessment method of large concrete dams is proposed and the problems for further research are pointed out.