An optimal seismic design method for base-isolated and fluid-filled pool structures subjected to random ground excitation is studied. The criterion selected for the optimization is minimum life-cycle cost. The damage cost is estimated based on the structural failure probability calculated by the stochastic response analysis. Prescribed values of the isolator displacement and the wall base shear force are predectermined to constitute the limit-state levels. Added mass matrix derived by FEM modeling is able to consider fluid-structure interaction effects between the flexible walls and contained fluid. Design variables for optimization are the wall thickness and isolator stiffness. Flexible isolator allows us to choose relatively thinner lateral wall with similar failure probability. The more flexible isolator is, the smaller failure probability and total life-cycle cost are. This optimal design case is insensitive to assumed damage cost scale.
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