ANALYTICAL ASPECTS OF BI-NORMALIZED RESPONSE SPECTRA BASED ON GROUND VELOCITY AND DISPLACMENT TIME HISTORIES IN NEAR FAULT

Near-fault ground motions have powerful impulsive nature which is characterized by long period and high amplitude pulses, relatively short durated and intensive strong waveforms as well as unusual spectral shape especially in lowfrequency band. The strong ground motion recorded within forward directivity process are qualitatively quite different from the far-field ones (Wuchuan et al., 2018). The strong near-fault ground motions have often waveform of pulses in the ground velocity history, so that in a time domain most of the kinematic energy considerably emanates through fault rupture mechanism. In this paper, the analytical aspects of bi-normalized response spectra (BNRS) according to the ground velocity and displacement in near fault has been notified and assessed numerically. The ground motions which are needed for this purpose have been selected based on the pulse-like records. The ensemble of the selected seismic tremors contains 16 records related to the Imperial Valley 1979 and the Northridge 1994 earthquake events. Moreover, BNRS of a symbolic single degree of freedom (SDOF) system was compared with corresponding normal response spectra (NSP). Toward this objective, the parameters including the kinematic energy ratio of fault parallel component (i.e. LN) to fault normal component (i.e. TR), peak ground velocity (PGV) and peak ground acceleration (PGA) were taken into account. Xu et al. (2004) proposed bi-normalized response spectrum based on performing statistical analyses on the records due to the 1999 Chi Chi earthquake. The study was concentrated on the interaction effects of soil conditions, epicentral distance, hanging wall and damping circumstances on the corresponding BNRS. Also, different criterions for normalizing the spectral period parameter (as oriented axis) have been investigated. Pavel et al. (2014) used predominant period and temporal control for assessing of bi-normalized velocity response spectra and notifications related to the dynamic amplification factor. Due to the importance of wavelike records, time duration of the distinct pulse can be an appropriate criterion for normalizing spectral period parameter (as oriented axis). In order to normalize the acceleration response spectrum, the numerical ratio of this spectra over a specific period (T) per the corresponding PGA must be applied. Hence, it can be resulted as bellow:(...)

کلیدواژه ها:

Bi-Normalized spectra ، Near fault ، Pulse-like ground motion ، Predominant period ، Jump up duration