Development of Reliability-based Seismic Design in Explicit Consideration of Variability of Structural Demand and Capacity

结构的安全性是通过保证抗震能力不小于抗震要求来实现的。由于地震作用的随机性以及结构及其构件的材料和几何特性的不确定性，结构的承载力和需求具有内在的可变性。本研究的目的是明确考虑这些随机性和不确定性的抗震设计程序。为此，进行了各种钢构件和框架试验，以量化这些构件和框架的强度和延性特性。重点讨论了构件和框架承受的极大变形和最终倒塌的行为。建立了一个通用框架模型，系统地进行数值分析，以量化以最大层间位移为特征的地震需求的中值和离散度。利用该模型并结合增量动力响应技术，安全极限，定义为没有成员持续恶化的极限，和倒塌极限，定义为结构不再承受重力荷载的极限，进行了检查。特别是，崩溃的边缘，定义为安全和崩溃极限之间的差异，被详细研究，并量化的强度和延性的个别成员的崩溃边缘的影响。柱脚是最具控制性的构件，对破坏边界的增大起着重要作用。并提供了钢梁、柱和柱脚的强度和延性计算公式。它们是构件细长度和板薄度以及柱和柱脚轴向荷载的函数。

The safety of structures is achieved by the assurance such that the seismic capacity shall not be smaller than the seismic demand. Both the capacity and demand possess inherent variability due to the randomness of seismic action and uncertainties of material and geometric properties of structures and their members. The goal of this research is to explicitly consider those randomness and uncertainties into the seismic design procedure. To this end, a variety of steel member and frames tests were performed to quantify both the strength and ductility characteristics of those members and frames. Emphasis is given onto the behavior of extremely large deformations and the ultimate collapse sustained by the members and frames. A generic-frame model was developed to systematically conduct numerical analyses for the quantification of both the median and dispersion of the seismic demand characterized by the maximum story drift. Using this model and combined with the incremental dynamic response technique, the safety limit, defined as the limit at which no member sustains deterioration, and the collapse limit, defined as the limit at which the structure no longer carry the gravity load, are examined. In particular, the collapse margin, defined as the difference between the safety and collapse limits, is looked into in detail, and effects of strength and ductility of individual members on the collapse margin are quantified. The column base is found to be the most controlling member in the enhancement of collapse margin. Practical design equations are also provided as for the strength and ductility evaluation of steel beams, columns, and column bases. They are given as a function of the member slenderness and plate thinness and the axial load for columns and column bases.