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Accelerogram processing using reliability bounds and optimal correction methods

Citation

Levine, Marie-Bernard P. (1990) Accelerogram processing using reliability bounds and optimal correction methods. Dissertation (Ph.D.), California Institute of Technology. http://resolver.caltech.edu/CaltechThesis:03112014-160752285

Abstract

This study addresses the problem of obtaining reliable velocities and displacements from accelerograms, a concern which often arises in earthquake engineering. A closed-form acceleration expression with random parameters is developed to test any strong-motion accelerogram processing method. Integration of this analytical time history yields the exact velocities, displacements and Fourier spectra. Noise and truncation can also be added. A two-step testing procedure is proposed and the original Volume II routine is used as an illustration. The main sources of error are identified and discussed. Although these errors may be reduced, it is impossible to extract the true time histories from an analog or digital accelerogram because of the uncertain noise level and missing data. Based on these uncertainties, a probabilistic approach is proposed as a new accelerogram processing method. A most probable record is presented as well as a reliability interval which reflects the level of error-uncertainty introduced by the recording and digitization process. The data is processed in the frequency domain, under assumptions governing either the initial value or the temporal mean of the time histories. This new processing approach is tested on synthetic records. It induces little error and the digitization noise is adequately bounded. Filtering is intended to be kept to a minimum and two optimal error-reduction methods are proposed. The "noise filters" reduce the noise level at each harmonic of the spectrum as a function of the signal-to-noise ratio. However, the correction at low frequencies is not sufficient to significantly reduce the drifts in the integrated time histories. The "spectral substitution method" uses optimization techniques to fit spectral models of near-field, far-field or structural motions to the amplitude spectrum of the measured data. The extremes of the spectrum of the recorded data where noise and error prevail are then partly altered, but not removed, and statistical criteria provide the choice of the appropriate cutoff frequencies. This correction method has been applied to existing strong-motion far-field, near-field and structural data with promising results. Since this correction method maintains the whole frequency range of the record, it should prove to be very useful in studying the long-period dynamics of local geology and structures.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:Accelerogram processing
Degree Grantor:California Institute of Technology
Division:Engineering and Applied Science
Major Option:Civil Engineering
Thesis Availability:Restricted to Caltech community only
Research Advisor(s):
  • Beck, James L.
Thesis Committee:
  • Beck, James L. (chair)
Defense Date:7 May 1990
Other Numbering System:
Other Numbering System NameOther Numbering System ID
EERL90-02
Record Number:CaltechThesis:03112014-160752285
Persistent URL:http://resolver.caltech.edu/CaltechThesis:03112014-160752285
Related URLs:
URLURL TypeDescription
http://resolver.caltech.edu/CaltechEERL:1990.EERL-90-02Related DocumentTechnical Report EERL 90-02 in CaltechAUTHORS
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:8127
Collection:CaltechTHESIS
Deposited By: Kathy Johnson
Deposited On:12 Mar 2014 21:51
Last Modified:13 Mar 2014 22:27

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