Earthquake Engineering for Concrete Dams Design, Performance, and Research Needs (1990) / Chapter Skim
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1. Introduction
1. Introduction
Pages 9-15
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From page 9... ...
(2) Knowledge of the complex nature of the earthquake motions that may attack a dam is increasing rapidly as more earthquake records are obtained all over the world, and it is becoming apparent that the seismic safety precautions taken in the past did not fully recognize the hazard.
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From page 10... ...
However, with expanding needs for water and with confidence derived from previous successful dam construction ventures, the sizes of dams grew, leading to increasing potential for disaster. Understanding of the changes in behavior associated with bigger dams tended to lag behind the increasing boldness of the planners, with the result that failures continued to occur with increasingly tragic consequences.
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From page 11... ...
: : :: ala ^.
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From page 12... ...
It was initiated by leakage in the contact zone between the impervious core material and the foundation rock; the leak quickly led to erosion of the embankment and caused total release of the reservoir within a few hours. The resulting flood produced property damage estimated at over one-half billion dollars, but fortunately flood warnings were issued early enough that only 14 lives were lost.
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From page 13... ...
Instrumentation within the dam recorded peak horizontal accelerations of 0.63 and 0.49 g in the crosschannel and the stream directions, respectively, and horizontal cracks caused by these motions appeared on both the upstream and downstream faces of the tallest nonoverflow blocks. They were located at the elevation where the slope of the downstream face changed, and subsequent dynamic finite element analysis demonstrated that such cracking was to be expected from an earthquake of the observed intensity.
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From page 14... ...
Subsequently, the analysis procedure was extended to treat the true dynamic character of the earthquake motions and the dynamic interaction of the dam with the reservoir water and foundation rock; then the aforementioned use of equivalent static loads was applied only in preliminary analyses. Present studies that take advantage of these advances in analytical procedures give greatly improved estimates of the seismic safety of existing or proposed concrete dams.
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From page 15... ...
is not considered in this report. It is assumed that geologists and seismologists will have established the magnitude and epicentral position of the greatest earthquake that must be considered in the seismic performance evaluation and that this information will have been applied, together with knowledge of the foundation rock properties, to obtain an estimate of the most intense free-field ground motions that may be expected in the vicinity of the dam.
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