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

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.