بررسي رفتار ديناميكي مخازن استوانهاي بتني ذخيره مايع تحت اثر حركت افقي و قائم زلزله

Study of seismic behavior of cylindrical concrete tanks under horizontal and vertical earthquale excitations

در اين مقاله، يك روش تحليلي براي برآورد پاسخ لرزه‌اي مخازن استوانه‌اي تحت تحريك افقي و قائم زلزله با در نظر گرفتن انعطاف-پذيري ديواره مخرن كه تا سطح خاصي از مايع پر شده‌اند، ارائه مي‌شود. حل مساله سيستم مايع-پوسته براي به‌دست آوردن فشار ضربه‌اي به‌روش ريلي-ريتز انجام مي‌گيرد. در تحليل ارتعاشي پوسته در حركت افقي زلزله اثر مدهاي محيطي نوع Cosθ و پوسته مخزن به‌صورت نازك در نظر گرفته شده است. همچنين نتايج اين روش تحليلي با نتايج مطالعات قبلي مقايسه مي‌شود. سپس با استفاده از روابط تحليلي پيشنهادي، يك مدل مكانيكي با در نظر گرفتن انعطاف‌پذيري جداره مخزن براي مخازن استوانه‌اي بتني تحت تحريك افقي زلزله ارائه مي-شود و نتايج اين مدل مكانيكي و دقت جواب حاصل از آن با نتايج تحليلي پيشنهادي و آيين‌نامه ACI 350.3-06 مقايسه مي‌شود. در انتها اين نتيجه حاصل مي‌شود كه جوابهاي آيين‌نامه با روش تحليلي پيشنهادي، تفاوت زيادي دارد كه علت آن در نظر نگرفتن صحيح انعطاف‌پذيري جداره توسط اين آيين‌نامه مي‌باشد.

Liquid storage tanks, as special structures, behave differently from ordinary structures in terms of dynamic behavior. These important structures are mostly constructed in two cylindrical and rectangular shapes, according to their use for storing various materials such as water and oil in the form of ground, elevated, buried and semi-buried. In this paper, an analytical method is presented for estimating the seismic responses of concrete cylindrical tanks subjected to horizontal and vertical components of earthquakes. Effects of liquid-shell interaction on the dynamic response of cylindrical tanks, taking into account flexibility of the wall and level of filling are studied. The velocity potential function is solved by satisfaction of boundary conditions and separating the variables. The solution of the problem is used to obtain the impulsive pressure using the Rayleigh-Ritz method using the vibration modes of flexible shells (open top-clamped bottom) with suitable boundary conditions. The results of this proposed analytical method are compared with those of the previous studies. Then a mechanical model is presented with considering the flexibility and mass of the tank wall for concrete cylindrical tanks completely or partially filled with liquid. The results of proposed mechanical model are compared with the analytical results and ACI 350.3-06. The conclusion is that while the design code does not estimate the response with a good accuracy, the proposed exact analytical procedure and the approximate mechanical model exhibit very good precisions for determining the dynamic responses of cylindrical concrete tanks.