Nonlinear treatment of liquid-filled storage tanks under earthquake excitation by a quasistatic approach

Liquid-filled storage tanks under earthquake excitation are loaded by hydrodynamic pressure due to the interactive motion with the containing fluid. The dynamic response and the buckling of these tanks have been studied by many authors both experimentally and theoretically, but a unified design procedure is still lacking. To gain insight more easily into the load carrying behavior and failure mechanism of anchored tanks, a quasistatic approach is presented in this paper instead of solving the coupled problem in the time domain. For these purposes, a nonlinear finite element procedure is applied using pressure eigenforms as equivalent loads. The numerical model used for the investigations is discretized by mixed ring shell elements taking geometric and physical nonlinearities into account. Different superpositions of the pressure eigenforms which are calculated by a special interactive model lead to different behavior of the tank-fluid system depending on the intensity of the horizontal and the vertical earthquake component. The results obtained are compared with classical values and with simplified design procedures provided in Eurocode 8, Part 4.