Abstract
Despite the various studies carried out to evaluate the effects of seismic sequences on structures, the matter of the time gap required to be considered between the mainshock and its corresponding aftershocks in dynamic analyses has never been focused on directly. This subtle but in the meantime effective subject, influences the amount of accumulated damage caused by earthquake sequences. In the present study, 244 near fault ground motion components from 122 earthquakes were applied to a wide variety of single degree of freedom systems having vibrating period of 0.05–7 seconds with linear and nonlinear behavior. Furthermore, 2 planar steel moment-resisting frames, having 3 and 12 stories, were subjected to a set of 30 ground motion components. The purpose of this investigation was to estimate the required time for the structures to cease the free vibration at the end of the mainshock. The main purpose is to generate an estimation that is function of structural system’s parameters and the strong motion duration. Excellent correlations were obtained between the rest time and the following parameters: the combination of natural period of single degree of freedom systems, as well as the strong motion duration of earthquake sequences. In consequence, a formula is proposed which estimates the optimized required rest-time of a structure based on natural vibration period, as well as the duration of strong motion. Additionally, results obtained from the dynamic analysis of the steel frames validate the rest-time values achieved by the proposed formula.
Highlights
The importance of aftershock effects on the responses of structures has been highlighted in several recent studies
Since the cost of analysis is of a great importance specially in the nonlinear time history analysis, an optimized estimation of the required time gap is necessary to be determined
For the vibration period of a system being equal to 7.0 s, the difference between the maximum rest time and minimum rest time, is around 20 s but the difference for a system with vibrating period of 1.0 s is close to zero value
Summary
The importance of aftershock effects on the responses of structures has been highlighted in several recent studies. A key feature in the application of seismic sequences within the dynamic analysis of structures, is the time gap of a certain length inserted between the mainshock and the corresponding aftershocks. This silent time interval with zero acceleration is applied in dynamic analysis to ensure that the structure ceases the free vibration followed by the elimination of the seismic excitation at the end of the ground motion’s time history (Goda 2012a, b). In other studies by Hatzigeorgiou (2010), a time gap of 100 s was applied between two consecutive seismic events (Hatzigeorgiou 2010a, b). In other studies by Hatzigeorgiou (2010), a time gap of 100 s was applied between two consecutive seismic events (Hatzigeorgiou 2010a, b). Moustafa and Takewaki (2011) applied the 40 seconds separating time interval between events (Moustafa and Takewaki 2011)
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