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seismic hazard and risk; ground motion models; Fourier amplitude spectrum; fragility
Abstract:
The relation between the response of an elastic single degree of freedom oscillator subject to seismic shaking and the
seismological characteristics of the input waveforms represented in terms of the Fourier amplitude spectrum (FAS) has
become a topic of growing interest in the engineering seismological community in recent years. As simulations of ground
motions assume a greater prominence in engineering design and databases of both strong and weak motion records expand
exponentially, the need to reconcile the influence of the controlling seismological properties of the motions with their
potential impacts on structural response is becoming ever more important. Prediction of ground motion in the Fourier
amplitude domain has several key advantages when compared to that of the response spectrum, namely a closer
relationship to the physical seismological properties of the source, path and site that can be inferred from more abundant
small magnitude and weak motion data, as well as maintained linearity of site response at all frequencies. Recognising
this, new empirical ground motion models have been developed in terms of FAS [1, 2], in addition to an inter-frequency
correlation model that can facilitate the definition of conditional spectrum compatible empirical and simulated ground
motion records for design [3]. In spite of these advantages, the usage of FAS in seismic hazard and risk analysis remains
limited to the scaling of simulated ground motions in the development of median ground motion models using random
vibration theory (RVT). One major factor behind this is that translation from FAS to response spectra via RVT requires
joint characterization not only of ground motions across a range of frequencies but also of strong motion duration.
However, this limitation could potentially be overcome if fragility functions were to be derived directly in terms of FAS.
It is for this purpose that a comparison is made in this paper between the efficiency of intensity measures based on the
FAS and those based on conventional response spectra for a set of simple building fragility models of the type commonly
used in seismic risk analysis. The feasibility of achieving end-to-end loss estimation exclusively in the Fourier amplitude
domain is subsequently explored. While its full range of benefits and limitations will require further study, the potential
for embedding seismological theory and data more deeply into engineering applications is appealing for the future practice
of seismic design and risk analysis.
