Directivity pulses in near-fault ground motions-Ⅱ: Estimation of pulse parameters

摘要

The simulation of directivity pulse-type ground motions through superimposition of modelled directivity pulse(s) on a non-pulse type motion is a possible approach to meet the scarcity of such motions in studying the structural response under those. It is shown in the companion paper that the amplitude and dominant Fourier period of the expected velocity pulse for a given seismic scenario may be sufficient to model the shapes of the expected acceleration and velocity pulses. Scaling models are proposed in this paper for the estimation of these parameters and time of occurrence of the expected pulse in the case of primary pulse, together with relationships between the parameters of the primary and secondary pulses. The pulses extracted in the companion paper are considered for this purpose. A sensitivity analysis shows that uncertainties in the estimation of the primary pulse parameters significantly affect the pseudo-spectral acceleration (PSA), non-linear maximum displacement (SD) and hysteresis energy dissipation (EH) responses to the simulated motions, whereas uncertainties in the primary-secondary pulse relationships affect only the SD response significantly. It has been shown that for a pulse-type motion, an increase in earthquake magnitude may sometimes lead to a significantly lower response. Further, the presence of a directivity pulse leads to a significantly greater response at lower magnitudes, and at higher magnitudes for the periods near the pulse period and in the case of a nonlinear response.