Earthquake Engineering for Concrete Dams Design, Performance, and Research Needs (1990) / Chapter Skim
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Executive Summary
Executive Summary
Pages 1-8
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The mandate of the panel was to evaluate the present status of knowledge about the earthquake performance of concrete dams, including procedures for investigating the seismic safety of such structures, and to summarize its findings in a report. The report was intended specifically to inform research workers about the state of the art of earthquake analysis of concrete dams and to identify subject areas where additional knowledge is needed.
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To establish the ultimate resisting capacity, however, damage mechanisms and the resulting nonlinearities must also be considered. Observational evidence provides the best indication of the true performance of a dam in the nonlinear response range; hence, one important part of earthquake engineering for concrete dams is the evaluation of data from dynamic tests real earthquake response information as well as laboratory and field test data.
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Because of the ability of the finite element method to define mathematical models with arbitrary geometries and variations of material properties, this method is usually adopted in formulating a mathematical model of a concrete dam. In this sense the seismic response analysis of a concrete dam
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The effect of these waves acting in the actual unbounded media will be to transmit energy away from the dam. Thus, a significant energy loss mechanism is not represented by the bounded finite element models of reservoir water and of foundation rock, and the development of mathematical models that properly account for these effects has become a major objective in research on the seismic behavior of concrete dams.
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From page 5... ...
OBSERVATIONAL EVIDENCE All analytical predictions of earthquake performance of concrete dams are based on numerous assumptions, each of which has a limited range of validity. Even the design of shaking-table experiments employing physical models of concrete dams requires the introduction of limiting assumptions, with regard to both the nature of the simulated earthquake motions to be applied and the properties of the model structure and of the foundation rock in which it is placed.
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From page 6... ...
Because real earthquakes provide the best test of earthquake performance, it is essential that many more existing concrete dams be provided with adequate seismic instrumentation so that quantitative evidence can be obtained to be used in verifying safety evaluation procedures. In addition, free-field instrumentation should be installed at potential concrete dam sites in regions of high seismicity so that better information can be obtained about the seismic excitation to which typical dams may be subjected.
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From page 7... ...
Now, with modern computer analysis procedures, it is possible to predict with some precision the linear elastic response that will result from a specified earthquake input; however, because of uncertainties in the characteristics of the expected earthquake, in the way the excitation is applied to the dam, in the dynamic strength properties of the concrete, and in the nature of the ultimate failure mechanism, it still is not possible to prescribe exactly the performance criteria to be used in the design of concrete dams. For this reason the criteria presently used in the seismic safety evaluation of existing concrete dams or in the design of new dams generally are simply stress checks in which the predicted elastic stress is compared with the expected concrete strength.
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From page 8... ...
Thus, it is evident that both analytical and experimental research on the nonlinear behavior of concrete dams continues to be of paramount importance.
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