Seismic Risk of Large Dams in Bulgaria

Abstract eng:
Most of the large dams in Bulgaria are situated in regions with high seismicity. The regulations that have been in force during the design and construction of the structures differ considerably from the modern codes. As a consequence a program for seismic assessment of the existing dams in Bulgaria has been prepared. It is essentially based on seismic risk assessment methodology. Because of the difference between the initial seismic design loads and the present code requirements a realistic analysis should be performed to take into consideration the capacity of the as-built structure. The methodology used for seismic risk assessment and the results reached are presented and discussed in the paper. The probabilistic seismic risk assessments for two concrete gravity dams and for one arch dam carried out recently are discussed. The obtained results are based on realistic assessment of the seismic hazard for the region, statistically and in-situ defined material properties and statistical definition of loads. For the aim of statistical characterization of the structure response under seismic excitation the Latin Hypercube Experimental Design (LHCED) procedure is used. The hydrostatic and hydrodynamic loads as well as the transient thermal loads are statistically represented. A list of failure scenarios for the dam is analyzed. As a result, the scenario with the highest probability of failure is determined. The acceptability of the probability of failure is discussed. In case of unacceptable probability of failure, measures for risk reduction are proposed.

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