Abstract
Near-source effects can amplify seismic ground motion, causing large demand to structures and thus their identification and characterization is fundamental for engineering applications. Among the most relevant features, forward-directivity effects may generate near-fault records characterized by a large velocity pulse and unusual response spectral shape amplified in a narrow frequency-band. In this paper, we explore the main statistical features of acceleration and displacement response spectra of a suite of 230 pulse-like signals (impulsive waveforms) contained in the NESS1 (NEar Source Strong-motion) flat-file. These collected pulse-like signals are analyzed in terms of pulse period and pulse azimuthal orientation. We highlight the most relevant differences of the pulse-like spectra compared to the ordinary (i.e., no-pulse) ones, and quantify the contribution of the pulse through a corrective factor of the spectral ordinates. Results show that the proposed empirical factors are able to capture the amplification effect induced by near-fault directivity, and thus they could be usefully included in the framework of probabilistic seismic hazard analysis to adjust ground-motion model (GMM) predictions.
Highlights
Near-fault effects are able to cause large seismic demand to structures compared to ground motion in far-field and their identification and characterization is fundamental for proper assessment of shaking for several engineering applications and seismic hazard analyses
In this paper we have shown the most relevant features of spectral response related to records affected by forward-directivity effects and calibrated a model for impulsive ground motions based on an empirical corrective factor
The main findings of the presented study include: (i) observations on the statistical features of pulse-like acceleration and displacement elastic spectra, (ii) a new near-source ground-motion model (GMM) of ordinary near-fault records and (iii) a new narrow-band amplification factor of elastic acceleration response that accounts for the increased seismic demand due to pulse-like effects
Summary
Near-fault effects are able to cause large seismic demand to structures compared to ground motion in far-field and their identification and characterization is fundamental for proper assessment of shaking for several engineering applications and seismic hazard analyses. We focus on forward-directivity effects identified by selecting the fullcycle pulses in the velocity time series, with the aim of investigating the pulse-like ground motion on spectral demand These effects have been widely studied by many authors from the phenomenological point of view [1,2,3,4,5,6]; they are not yet fully included in the context of Probabilistic Seismic Hazard Analyses (PSHA) and the current seismic design codes do not provide a proper representation of these effects. We modelled the narrow-band directivity factor based on the within-event part of the model residuals (i.e., the logarithmic difference between the observations and the model predictions) computed on a reference GMM calibrated on the no-pulse (ordinary) records of the same dataset
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