Numerous aftershocks can be triggered by a strong mainshock and may cause more severe and widespread structural damage with respect to a single seismic event. This study investigates the effect of relative differences between the incident angles of consecutive earthquakes on seismic demands of structures as bi-linear Single-Degree-Of-Freedom (SDOF) systems. To this aim, constant-strength spectra are developed based on different Normalized Engineering Demand Parameters (NEDPs) to identify this impact as a new seismic uncertainty. Several seismic sequences with one aftershock and also two aftershocks are generated considering different directions of both mainshocks and subsequent aftershocks as input excitations in nonlinear dynamic analyses of SDOF systems. The results demonstrate that taking into account the relative differences of the incident angles of sequential earthquakes can affect significantly seismic responses.

强烈的主震可能会引发许多余震，并且就单个地震事件而言，可能会导致更严重，更广泛的结构破坏。这项研究调查连续地震的入射角之间的相对差异对双线性单自由度（SDOF）系统的结构的地震需求的影响。为此，根据不同的标准化工程需求参数（NEDP）开发了恒定强度谱）将此影响识别为新的地震不确定性。在SDOF系统的非线性动力分析中，考虑主震和不同方向的余震的不同方向，产生了带有一个余震和两个余震的几个地震序列。结果表明，考虑到连续地震入射角的相对差异会显着影响地震响应。