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UBC Theses and Dissertations
Dynamic behavioir of base cracked gravity dam by the way of the hybrid frequency time domain procedure Hui, Pak K.
Abstract
Due to deterioration, past loading conditions, and shrinkage, concrete tensile cracks may form along the dam-foundation interface within a typical concrete gravity dam monolith. These cracks render the assumption that a dam remains linear elastic during dynamic response invalid and requires a nonlinear analysis procedure. In this research, the response of the cracked dam system with the effects of a flexible foundation and hydrodynamic effects is studied using the Hybrid Frequency Time Domain (HFTD) analysis procedure. This nonlinear dynamic analysis procedure preserves the frequency dependent stiffness and damping in the foundation medium when modeled as a visco-elastic halfplane. Similarly, the HFTD procedure honours the frequency dependent hydrodynamic mass and damping of the reservoir medium when the hydrodynamic effects are modeled with a two dimensional wave equation. The nonlinear behavior of the crack opening and closing process is directly accounted for by applying the required restoring or contact force along the crack interface. The result of the study shows that dams with crack lengths less than 25% of the total base length have nominal differences in both magnitude and frequency of vibration when compared to the same uncracked system. For crack lengths in excess of 25%, larger response amplifications than those from the uncracked response were observed. The fundamental effective system frequency of vibration of the cracked dam system is found to be bounded by fundamental frequencies of the uncracked and cracked pseudo-linear systems of the dam. Large amplifications of the maximum dam top response obtained from the cracked system in comparison to the uncracked system are expected for systems near the dominant frequency of excitation. However, for systems with properties that are far removed from the dominant frequency of excitation, little, if any, amplification of the peak response is evident for all crack lengths. A simplified approach of representing the cracked dam system as a SDOF system with bi-linear stiffness proves to be an efficient and accurate method of estimating the cracked dam displacement and velocity response. The speed of the procedure allows for preliminary assessments to be made prior to dedicating valuable time to a full nonlinear analysis. In addition, this procedure can be used to produce cracked response spectra which can accurately predict the amplifications expected in the maximum relative displacement and velocity in a cracked dam system as compared to an uncracked dam system.
Item Metadata
Title |
Dynamic behavioir of base cracked gravity dam by the way of the hybrid frequency time domain procedure
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Creator | |
Publisher |
University of British Columbia
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Date Issued |
1995
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Description |
Due to deterioration, past loading conditions, and shrinkage, concrete tensile cracks may form
along the dam-foundation interface within a typical concrete gravity dam monolith. These
cracks render the assumption that a dam remains linear elastic during dynamic response invalid
and requires a nonlinear analysis procedure. In this research, the response of the cracked dam
system with the effects of a flexible foundation and hydrodynamic effects is studied using the
Hybrid Frequency Time Domain (HFTD) analysis procedure. This nonlinear dynamic analysis
procedure preserves the frequency dependent stiffness and damping in the foundation medium
when modeled as a visco-elastic halfplane. Similarly, the HFTD procedure honours the
frequency dependent hydrodynamic mass and damping of the reservoir medium when the
hydrodynamic effects are modeled with a two dimensional wave equation. The nonlinear
behavior of the crack opening and closing process is directly accounted for by applying the
required restoring or contact force along the crack interface. The result of the study shows
that dams with crack lengths less than 25% of the total base length have nominal differences in
both magnitude and frequency of vibration when compared to the same uncracked system.
For crack lengths in excess of 25%, larger response amplifications than those from the
uncracked response were observed. The fundamental effective system frequency of vibration
of the cracked dam system is found to be bounded by fundamental frequencies of the
uncracked and cracked pseudo-linear systems of the dam. Large amplifications of the
maximum dam top response obtained from the cracked system in comparison to the uncracked
system are expected for systems near the dominant frequency of excitation. However, for
systems with properties that are far removed from the dominant frequency of excitation, little, if any, amplification of the peak response is evident for all crack lengths. A simplified
approach of representing the cracked dam system as a SDOF system with bi-linear stiffness
proves to be an efficient and accurate method of estimating the cracked dam displacement and
velocity response. The speed of the procedure allows for preliminary assessments to be made
prior to dedicating valuable time to a full nonlinear analysis. In addition, this procedure can be
used to produce cracked response spectra which can accurately predict the amplifications
expected in the maximum relative displacement and velocity in a cracked dam system as
compared to an uncracked dam system.
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Extent |
6683162 bytes
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Genre | |
Type | |
File Format |
application/pdf
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Language |
eng
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Date Available |
2009-01-30
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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 |
10.14288/1.0050381
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URI | |
Degree | |
Program | |
Affiliation | |
Degree Grantor |
University of British Columbia
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Graduation Date |
1995-11
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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.