پيشنهاد روش تخمين فشار هيدروديناميكي براي طراحي لرزه‌اي دريچه سازه‌هاي هيدروليكي مجاور مخزن

Suggested Estimating Method for Hydrodynamic Pressure to Seismic Design of Hydraulic Structure Gates in Adjacent To Dam Reservoir

چكيده- ايمني همه‌ي سدها به كارايي و قابل اطمينان بودن سازه‌هاي جانبي آن بستگي دارد. يكي از اصلي‌ترين سازه‌هاي جنبي كه جريان آب درون مخازن سدها را كنترل مي‌كند؛ دريچه‌ها است. زلزله موجب پيدايش امواج هيدروديناميك در مخزن پشت سد مي‌شود و فشارهايي بيش از فشار هيدرواستاتيكي را به سد و سازه‌هاي وابسته به آن وارد مي‌كند. دريچه‌اي كه روي بدنه سد نصب مي‌شود، به‌خاطر انعطاف‌پذيري بيشتر نسبت به بدنه سد، هنگام زلزله، نوساناتي جدا از نوسانات بدنه اصلي سد خواهد داشت. در اين مقاله به كمك طيف طبقه زلزله در تراز دريچه كه در طراحي سامانه‌هاي ثانويه استفاده مي‌شود و پارامتر شتاب طيفي در تراز دريچه كه بر اساس بسامد غالب دريچه - مخزن محاسبه مي‌شود، رويه رايج براي طراحي دريچه‌ها اصلاح شده و بر مبناي ارزيابي‌هاي انجام‌شده و پخش نرمال داده‌هاي به‌دست آمده، از محاسبات مفصل عددي مدل سد- دريچه- مخزن ضريب بدون بعد جديدي براي تعيين فشار هيدروديناميكي دريچه‌هاي مستطيلي لغزنده در تراز‌هاي مختلف بدنه سد پيشنهاد مي‌شود.

Abstract: No dam could be safely designed without functionality dependence on reliable performance of a number of appurtenant structures. Gates are the main appurtenant structures responsible for controlling water flow from the reservoir. Earthquakes induce acoustic and surface waves in the reservoir and cause hydrodynamic pressure on the adjacent gates. Hydrodynamic pressures might surpass hydrostatic pressure on some locations of the dam upstream face. Some engineers use the hydrodynamic pressure solution concerning to axi-symmetric offshore and coastal structures for the design of such hydro-mechanical gates. Flexibility of these gates may magnify the hydrodynamic pressure due to severe generation of vibrations separate from the dam body itself even for those installed within the dam bodies. This statement reflects the design philosophy of secondary structures. Fundamental frequency of such gates are usually reduced due to the presence of infinite fluid in their vicinity. Therefore the study of their behavior is somehow complicated during the earthquake. Design regulations of hydraulic structures, demand the hydrodynamic pressure as a design action and usually admits its simple calculation from the Westergaard formula. In this article, by using floor response spectrum in gate level which is used to design the secondary systems and also the spectral acceleration parameter in gate level which is used based on predominant frequency of gate-reservoir, the common relation of gate design against hydrodynamic pressure has been corrected. Then a new non-dimension factor is suggested for sliding rectangular gates in different levels of dam body that is related to the performed analyses and log-normal distribution of data.. In general for various conditions the dimensionless coefficient of Westergaard formula changes from 0.875 to widely varying values between 0.25 to 2.5 when using the base acceleration. However when the spectral acceleration of the floor response spectrum is used for the fundamental frequency of gate-reservoir, this coefficient is more precisely determined for vertical rectangular gates.