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Ambient vibration assessment of Ruskin Dam dynamic properties Kemp, Bradley Gary
Abstract
Concrete gravity dams are significant civil engineering structures whose failure can produce catastrophic results. Field appraisal of their dynamic properties would be useful to validate numerical models used for structural analysis to determine, for instance, seismic resistance. The suitability of ambient vibration testing and analysis to provide meaningful dynamic properties of a concrete gravity dam has been studied. Tests were conducted at B.C. Hydro's Ruskin Dam, located near Mission, B.C. Tests were completed at two reservoir levels to permit calibration of a numerical model. Two distinct methods of frequency domain based analysis were used to determine dynamic properties. The first method used proven ambient vibration techniques, based on a "relative" single inputsingle output system, with no quantification of excitation. Relative transfer function relationships were constructed between a reference location on the dam and all other points on the dam at which measurements were taken. The selection of potential natural frequencies was completed by consideration of the power in the signals recorded. Final selection of natural frequencies and associated mode shapes was based on the resulting gain, phase and coherence values of the relative transfer functions. In the second method, the field measurements were considered to represent a single inputsingle output system with output noise, as the bedrock signal was shown to represent the majority of input. For this approach, natural frequencies were indicated as peaks in crossspectral density functions with high coherence and corresponding transfer functions having phase factors equal to 90 degrees. Two natural frequencies and corresponding mode shapes were identified. Confidence of prediction was found to be highest for the first of these. Although this was concluded to be a meaningful result, there is clearly a need for developing additional ambient vibration theory which can be implemented to identify dynamic properties. To demonstrate the usefulness of the dynamic properties obtained through the ambient vibration testing and analysis, a numerical model of the dam utilizing the finite element method was subjected to modal analysis with which to complete calibration/parametric studies. Calibration was found successful only for the first natural frequency, probably because the numerical model failed to include the effects of water compressibility, which were shown through rudimentary calculations to be significant. Calibration to the first natural frequency is, however, considered meaningful as concrete gravity dam response is attributed mainly to the fundamental mode.
Item Metadata
Title |
Ambient vibration assessment of Ruskin Dam dynamic properties
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Creator | |
Publisher |
University of British Columbia
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Date Issued |
1996
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Description |
Concrete gravity dams are significant civil engineering structures whose failure can produce
catastrophic results. Field appraisal of their dynamic properties would be useful to validate
numerical models used for structural analysis to determine, for instance, seismic resistance.
The suitability of ambient vibration testing and analysis to provide meaningful dynamic
properties of a concrete gravity dam has been studied. Tests were conducted at B.C. Hydro's
Ruskin Dam, located near Mission, B.C. Tests were completed at two reservoir levels to
permit calibration of a numerical model. Two distinct methods of frequency domain based
analysis were used to determine dynamic properties.
The first method used proven ambient vibration techniques, based on a "relative" single inputsingle
output system, with no quantification of excitation. Relative transfer function
relationships were constructed between a reference location on the dam and all other points
on the dam at which measurements were taken. The selection of potential natural frequencies
was completed by consideration of the power in the signals recorded. Final selection of
natural frequencies and associated mode shapes was based on the resulting gain, phase and
coherence values of the relative transfer functions.
In the second method, the field measurements were considered to represent a single inputsingle
output system with output noise, as the bedrock signal was shown to represent the
majority of input. For this approach, natural frequencies were indicated as peaks in crossspectral
density functions with high coherence and corresponding transfer functions having phase factors equal to 90 degrees.
Two natural frequencies and corresponding mode shapes were identified. Confidence of
prediction was found to be highest for the first of these. Although this was concluded to be a
meaningful result, there is clearly a need for developing additional ambient vibration theory
which can be implemented to identify dynamic properties.
To demonstrate the usefulness of the dynamic properties obtained through the ambient
vibration testing and analysis, a numerical model of the dam utilizing the finite element
method was subjected to modal analysis with which to complete calibration/parametric
studies. Calibration was found successful only for the first natural frequency, probably
because the numerical model failed to include the effects of water compressibility, which
were shown through rudimentary calculations to be significant. Calibration to the first natural
frequency is, however, considered meaningful as concrete gravity dam response is attributed
mainly to the fundamental mode.
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Extent |
17232354 bytes
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Genre | |
Type | |
File Format |
application/pdf
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Language |
eng
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Date Available |
2009-02-06
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Provider |
Vancouver : University of British Columbia Library
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Rights |
For non-commercial purposes only, such as research, private study and education. Additional conditions apply, see Terms of Use https://open.library.ubc.ca/terms_of_use.
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DOI |
10.14288/1.0050339
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URI | |
Degree | |
Program | |
Affiliation | |
Degree Grantor |
University of British Columbia
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Graduation Date |
1996-05
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Campus | |
Scholarly Level |
Graduate
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Aggregated Source Repository |
DSpace
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Item Media
Item Citations and Data
Rights
For non-commercial purposes only, such as research, private study and education. Additional conditions apply, see Terms of Use https://open.library.ubc.ca/terms_of_use.