Steel moment-resisting frames (MRFs) are designed to resist a design-level single seismic event. However, every earthquake may be accompanied by several foreshocks or aftershocks. The cyclic deterioration of structural elements during early earthquakes may cause the lateral-load-resisting system to collapse under the mainshock or aftershocks. The differences in the seismic performance of special and intermediate MRFs (here called SMFs and IMFs, respectively) subjected to single and multiple earthquake events were investigated. For this purpose, four perimeter steel MRFs with four and eight storeys were designed and subjected to 22 synthesised multi-record earthquake events. The non-linear modelling technique adopted accounts for the cyclic deterioration of structural elements, which is a key parameter in the evaluation of seismic performance under sequential earthquakes. The results showed that structural collapse capacity may be reduced considerably if the structure is subjected to foreshock and aftershock events in addition to the mainshock. In addition, it was found that, for the IMF models, the switch from the life safety (LS) limit state to the collapse prevention limit state was immediate. Therefore, the design of IMFs for the LS performance level may result in a substantial risk of collapse when the structure is exposed to repeated earthquakes.

中文翻译：

---

重复地震作用下特殊和中间力矩框架响应的比较

钢制抗弯框架 (MRF) 旨在抵抗设计级的单一地震事件。然而，每次地震都可能伴有数次前震或余震。早期地震中结构构件的循环劣化可能导致抗侧向荷载系统在主震或余震下坍塌。研究了特殊和中间 MRF（这里分别称为 SMF 和 IMF）在单次和多次地震事件下的抗震性能差异。为此，设计了四个四层和八层的周边钢 MRF，并对其进行了 22 次合成多记录地震事件。所采用的非线性建模技术解释了结构元素的循环恶化，是连续地震作用下抗震性能评价的关键参数。结果表明，如果结构除了主震外还受到前震和余震事件的影响，结构的倒塌能力可能会大大降低。此外，发现对于 IMF 模型，从生命安全 (LS) 极限状态到防倒塌极限状态的切换是立即的。因此，针对 LS 性能水平的 IMF 设计可能会在结构暴露于反复地震时导致重大的倒塌风险。从生命安全（LS）极限状态到防倒塌极限状态的切换是立即的。因此，针对 LS 性能水平的 IMF 设计可能会在结构暴露于反复地震时导致重大的倒塌风险。从生命安全（LS）极限状态到防倒塌极限状态的切换是立即的。因此，针对 LS 性能水平的 IMF 设计可能会在结构暴露于反复地震时导致重大的倒塌风险。