Abstract In a seismic event, large number of aftershocks are generally triggered due to the complex interaction within and between tectonic plates. Even though aftershocks are typically smaller in magnitude than mainshocks, their ground-motion intensity, measured by peak ground acceleration, is not always smaller. Moreover, mainshocks can result in permanent damage to structural components. As a result, the vulnerability of structures to extensive damage and complete collapse due to aftershocks could increase. Despite their importance in evaluating the true risk of system failure and collapse, the inclusion of aftershocks in code provisions and guidelines for seismic risk assessment and performance-based engineering is lacking. In this study, three semi-rigid frames, with connection capacities of 50%, 60%, and 70% of the plastic moment of the beam, were designed and their performance under mainshock-aftershock sequences assessed. The objective of this study, pertaining to the seismic performance of the frames, is twofold. First, is to develop fragility functions for the subject frames under sequential mainshock-aftershock events. Second, is to evaluate the extent of spread of inelasticity and period elongation in the investigated frames as a result of the sequential events. A new method for selection and scaling of mainshock-aftershock sequences is proposed and non-linear time history analysis of the frames is conducted. The results show that the inclusion of the aftershocks increases the probability of reaching or exceeding a particular damage limit state in the frames, primarily due to the considerable period elongation resulting from the induced permanent damages.

中文翻译：

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半刚性钢框架对连续地震的响应

摘要 在地震事件中，由于构造板块内部和板块之间的复杂相互作用，通常会引发大量余震。尽管余震的震级通常小于主震，但它们的地面运动强度（以峰值地面加速度衡量）并不总是较小。此外，主震可能对结构部件造成永久性损坏。因此，结构因余震而遭受大面积损坏和完全倒塌的脆弱性可能会增加。尽管余震在评估系统故障和崩溃的真实风险方面很重要，但在地震风险评估和基于性能的工程的规范规定和指南中缺乏余震的内容。在这项研究中，三个半刚性框架，连接能力分别为梁塑性弯矩的 50%、60% 和 70%，设计并评估了它们在主震-余震序列下的性能。这项研究的目的是关于框架的抗震性能，有双重目的。首先，是在连续的主震 - 余震事件下开发主题框架的脆弱性函数。其次，是评估由于连续事件导致的调查框架中非弹性和周期延长的扩散程度。提出了一种主余震序列选择和标度的新方法，并进行了框架的非线性时程分析。结果表明，包含余震增加了框架中达到或超过特定损坏极限状态的可能性，这主要是由于诱发的永久损坏导致相当大的周期延长。