FREQUENCY OPTIMIZATION OF CONCRETE ARCH DAMS USING THE RESULTS OF VIBRATION TESTS and MATHEMATICAL MODEL

Conducting experimental investigations for recognition of concrete dams behavior under dynamic loads e.g. earthquakes or natural phenomena is of paramount importance. This issue may be considered as one of the most strategic goals in the branch of water industry of our nation. In the present research characteristic and dynamic behavior of a concrete arch dam (Shahid Rajaee Dam) has been investigated under the ambient and forced vibration tests, and the results have been compared with those of the mathematical model. Using a consistent algorithm developed in this research we processed the records obtained from the tests performed. In analysis of the mathematical model of the whole dam-reservoir-foundation system effects of different non-deterministic parameters as equivalent (average) elasticity modulus of concrete and rock, water compressibility, foundation mass distribution pattern, Poisson ratio of concrete and rock, etc. were studied. The target of the sensitivity study was based on natural frequencies. The important results, which were obtained, show that the assumption of water incompressibility would strongly influence the natural frequencies of the system particularly on higher modes. For better calibration of the mathematical model a frequency optimization process was performed. As a result of this investigation the four first modes of the system were obtained from the ambient vibration tests. These proved a good agreement with those of the mathematical model.