关于概率地震需求模型的讨论

概率地震需求分析作为地震易损性分析和地震风险分析的重要一环，已经成为新一代基于性能地震工程(PBEE)的主要研究内容。概率地震需求分析的核心内容是建立概率地震需求模型，它表征了地震动强度与地震需求之间的概率关系。在某一强度地震动作用下，通常假设地震需求服从对数正态分布，其中，地震需求的中位值和地震动强度之间假设服从对数线性关系，而地震需求的对数标准差则假设保持不变。该文以4个不同高度、不同设防水准的钢筋混凝土框架结构为例，挑选100条实际地震动为输入，针对上述概率地震需求模型基本假设的合理性进行了讨论。研究结果表明:综合考虑计算精度和效率，关于地震需求中位值和对数标准差的假设可以满足概率地震需求模型的要求，而传统的对数正态概率地震需求模型无法考虑倒塌的影响，应予以修正。

DISCUSSIONS ON PROBABILISTIC SEISMIC DEMAND MODELS

As an important element of seismic fragility and risk analysis, the probabilistic seismic demand analysis has become a main component of the new-generation of performance-based earthquake engineering (PBEE). The key issue of probabilistic seismic demand analysis is to derive a probabilistic seismic demand model, that denotes the probabilistic relationship between earthquake intensity and seismic demand. Given a specified level of earthquake intensity, seismic demand is generally assumed to submit to a lognormal distribution. A log-line relationship is assumed between earthquake intensity and the median value of seismic demand, while the logarithm standard deviation of seismic demand is assumed invariant. In order to examine the validity of the above assumptions adopted in the probabilistic seismic demand model, four RC frame buildings of various heights and fortification levels are taken as test beds, and one hundred real ground motions are selected as inputs. The results show that the assumptions of the median and logarithm standard deviation of seismic demand are adequate for a probabilistic seismic demand model considering the balance of accuracy and efficiency. However, the conventional lognormal model for seismic demand cannot incorporate the case of collapse, thus it should be modified.