Effects of incident angles of earthquake sequences on seismic demands of structures

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