Reliability-Based Optimal Design of Fluid Filled Tanks Under Seismic Excitation

This work integrates developments in simplified dynamic modeling of unanchored fluid-filled tanks, stochastic modeling of earthquake loading time histories, probabilistic structural analysis tools, cost analyses, and multi-criteria optimal design formulations for the design optimization of unanchored fluid-filled cylindrical tanks operating in an uncertain seismic environment. An appropriate simplified mechanical model is developed which includes effects from the sloshing at the liquid free surface, the soil flexibility and the separation of the base plate of the tank from its foundation, which occurs during strong ground motion. A class of stochastic processes with frequency content and time-varying intensity characteristics determined by seismological parameters is used to model the earthquake loading time history. The reliability of the cylindrical tank against failure of the shell structure is computed using latest developments in efficient Monte Carlo simulation methods. A multi-criteria design optimization methodology is then used to obtain the optimal design characteristics of the tank system that meet cost and reliability constrains. Issues related to reliability estimation and optimization are addressed. The methodology is useful for optimally designing fluid-filled structures that operate in a seismic environment to withstand earthquakes with minimal social and economical losses during the lifetime of the structure.