Probabilistic Evaluation of Column Over-Design Factore for Fram Structures

在框架结构的抗震设计中，全破坏模式下的梁先屈服、柱先屈服的模式被认为是一种较好的模式。因此，结构通常采用弱梁强柱设计，并带有柱超设计系数。但在实际工程中，由于外荷载和构件强度存在较大的不确定性，所设计的弱梁强柱结构可能不会按理想的破坏模式倒塌。这些不确定性可能会改变柱的超设计系数（COF），结构可能会根据一些不利的破坏模式，如薄弱层机制。本研究的目的是概率评估柱超设计系数的目标值，对于该目标值，不良失效模式的发生概率可以限制在特定的公差范围内。采用线性规划法和一阶可靠度法建立了一种随机极限分析方法，并对弱梁强柱结构的可能破坏模式进行了分析。从概率的角度讨论了柱超设计系数的目标值。据发现，一个更高的值的柱超设计系数是需要在不确定的负载和成员的强度的情况下，比预期的确定性的情况下。

In the earthquake resistance design of frame structures, the mode in entire failure pattern, which allows the yielding of all the beams in flexure prior to possible yielding of columns, is generally considered to be a preferable mode. Structures are therefore generally weak-beam-strong-column designed with a column over-design factor. In reality however, the designed weak-beam-strong-column structures may not collapse according to the preferable failure mode because of the large uncertainties in the external loads and the member strengths. These uncertainties may change the column over-design factor (COF) and the structure may collapse according to some unpreferable failure modes such as the weak story mechanisms. The object of this study is probabilistic evaluation of the target values of column over-design factors for which the occurrence probability of unpreferable failure modes can be limited to within a specific tolerance. A stochastic limit analysis procedure using the Linear Programing method and the First Order Reliability Method is developed, and the likely failure modes of weak-beam-strong-column designed structures are investigated using this procedure. The target value of column over-design factor is discussed in probabilistic terms. It is found that a much higher value of column over-design factor is required in the case of uncertain loads and member strengths than is expected in deterministic cases.