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Contemporary issues in earthquake engineering research: processing of accelerometric data, modelling of inelastic structural response, and quantification of near-fault effects

Ágúst 2011

This study focuses on three contemporary issues related to the fields of Earthquake
Engineering and Engineering Seismology: (1) processing acceletometric data and
assessing permanent ground displacements, (2) modelling the response spectra of
inelastic structures, and (3) quantifying near-fault ground-motion effects relevant to
engineering structures.
Most of the noise in accelerometric data can be removed by standard signal processing,
for example, low-pass and high-pass filters. High-pass filters, if used to adjust
baseline errors, can result in inadvertent loss of long-period signal due to, for example,
permanent ground displacements in the near-fault area. Despite several efforts,
a consistent and well-defined method to adjust baseline errors without losing a part
or the whole of permanent displacements (if any) is not available in the literature.
This study develops and thoroughly tests such a method by using several near-fault
An inelastic response spectrum is required in the design of earthquake-resistant structures.
In the current practice, it is obtained by scaling an elastic response spectrum
by some ad-hoc factors, such as, structural behaviour factor, or force reduction factor.
This approach lacks a rational basis and is highly uncertain. This study shows
that inelastic response spectra can be modelled in a manner similar to elastic response
spectra by calibrating Ground-Motion Prediction Equations (GMPEs) for
inelastic structures. This is achieved by regressing peak responses of inelastic structures
against earthquake parameters (such as, size, faulting mechanism, etc.), path
parameters (such as, source-to-site distance), site parameters (such as soil conditions),
and structural parameters (such as, undamped natural period of vibration,
damping ratio, displacement ductility, yield strength, etc.). The resulting GMPEs
can be applied in Probabilistic Seismic Hazard Assessment (PSHA) and Probabilistic
Seismic Demand Assessment (PSDA) to estimate uniform-hazard representations of
design forces and ductility demands with greater reliability and accuracy than by
traditional methods.
Near-fault ground motions affected by forward-directivity effects, which are on the
focus of this study, contain most of their energy in a narrow frequency band, and
therefore affect certain structures more severely than others. To ensure reliable design/
evaluation of structures, important properties of near-fault ground motions, such
as their amplitude and frequency content, need to be properly quantified. In this
study, peak ground velocity (PGV) and predominant period (Td) of ground motion
are used to characterize near-fault ground motions. Mathematical models relating
PGV and Td to earthquake size, source-to-site distance, etc, are calibrated using a
large set of near-fault ground-motion data. These parameters, along with structural
properties, such as, undamped natural period and damping ratio of an oscillator, are
used to quantify the elastic as well as inelastic response spectra of pulse-like ground
motions in the near-fault area more adequately than was possible using earlier approaches.


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