Page - 1103 - in Book of Full Papers - Symposium Hydro Engineering

this study the relationships of Campbell & Bozorgnia [3], Ambraseys and Douglas [4], Boore et al. [5] and Mahdavian [6] were used. 3.3. GROUND MOTION DESIGN LEVELS Four ground motion levels were considered to define the seismic design requirements for the power plant and appurtenant structures. These design levels are partly defined by International Committee of Large Dams [7] and Building and Housing Research Center of Iran [8]. The basic idea is to allow for certain damages during an earthquake of a relatively long return period compared to the lifetime of the structure but not to endanger people’s life. The four ground motion levels are defined in following on. 3.3.1. Operating Basis Level (OBL) The Operating Basis earthquake is expected to occur during the lifetime of the dam. The OBE represents the level of ground motion at the dam site which no damage is acceptable. In this study recommended return period of occurring of the OBE is about 150 years. 3.3.2. Design Basis Level (DBL) Ground motions of this level are expected to occur during the lifetime of the power plant. Some minor damage to structures and equipment is accepted but they must remain functional. A PSHA is the most suitable method to establish this level and a return period is about 500 years (usually 475 years). 3.3.3. Maximum Design Level (MDL) This level of ground motions has a low probability of occurrence with a return period of about 1000 years. The dam and appurtenant structures shall be able to resist these ground motions but larger damages are accepted. Safety related devices, such as spillway gates, must remain operational. PSHA is most appropriate to establish values for this ground motion level. 3.3.4. Maximum Credible Design Level (MCL) 1103