SEISMIC ANALYIS OF CONCRETE ARCH DAMS - TWO CASE STUDIES

Abstract

In the framework of the Portuguese National Programme for Dams with High Hy- droelectric Potential (PNBEPH), a set of large concrete dams is currently under design or construction, including several 100 m high arch dams. Earthquake loading is one of the im- portant aspects to be considered in the design of these structures. A variety of numerical methods have been developed over the years by various researchers and are presently availa- ble for seismic analysis of concrete dams. The methods in use by the dam engineering com- munity have different approaches, for example, in the representation of the seismic action, the dam-water interaction or the structural nonlinear behavior. In the paper, the models applied in the study of new Portuguese dams are presented, and their fundamental assumptions dis- cussed. In particular, the analysis of the response of arch dams to the Maximum Design Earthquake is examined, considering the non-elastic behavior of the contraction joints and the dam foundation. An explicit time integration algorithm was used in these simulations, allowing a detailed representation of the slip and separation events along the discontinuities. The boundary conditions appropriate for seismic analysis are discussed, namely the type of free-field boundaries employed. In the paper, the application of this modeling methodology to two new dams is presented and discussed. Foz Tua dam, that is already under construction, is a concrete arch dam, 108 m high and 275 m long at the crest. Fridao dam is also a concrete arch dam, 98 m high and with a crest length of 300 m. Design criteria and the results of the numerical analyses are discussed.