周锡元^1,2   曾德民¹   高晓安¹
  （1 中国建筑科学研究院  北京 100013；   2 北京工业大学  100022）

[提要]  对现行建筑抗震设计规范中三个设防水准的概率含义进行了讨论。指出除基本烈度地震以外，另外两个水准的概率含义是不明确的，只能从平均意义上去理解。根据规范中考虑的三个概率水准的设防烈度之间的平均相互关系，建议了一种可以用于估计不同服役期结构抗震设防烈度的简便方法。这样确定的设防烈度虽然不能很好反映当地的实际情况，但是可以反映设防烈度随服役期限变化的一般趋势，故可作为确定一般工程设防烈度的参考。此外，还讨论了建立与三水准设防相对应的基本加速度和设计反应谱放大倍数。
[关键词]  抗震设计  预期服役期  重现期  结构重要性

The probabilistic meanings of three levels of earthquake protection in seismic design code for buildings are discussed. It is pointed out that except basic design earthquake intensity the probabilistic definition of the two levels of earth-quake protection is ambiguous that can only be understood in average meaning. On basis of mutual relations among three level probabilistic earthquake protection intensities, which are considered in seismic design code,  a simplified method for estimating design basic intensity of structures with different service period and acceptable hazard level is presented. The estimated design intensity corresponding to different return period in this way is unable to reflex the real situation of the local seismisity of the considered site, but gives a general assessment of the basic design intensity. Hence it can be used as reference for determining design intensity of normal structures.  In addition, the basic design accelerations and amplification factors in accordance with three level design intensities are also discussed.
Keywords:  seismic design; expected service period; return period; structural importance