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Inverted pendulum-like structures such as elevated tanks are not only subjected to overturning moments from lateral seismic forces, but also from P-Δ effect which originates due to gradual shifting of line of actions of gravity loads due to largely increasing inelastic displacements, causing progressive increase in the tendency of overturning in the inelastic range. The response reduction factors are prescribed in the code to limit the inelastic displacement demands of the structures depending on their ductility capacities. In this context, the present study investigates the influence of P-Δ effect on elevated tanks. The study attempts to propose a simple enough mathematical model to assess the comparative difference in lateral displacement and overturning moment due to consideration of progressive P-Δ effect with and without computed through nonlinear response history analysis. Two typical hysteresis behaviors, namely, elastoplastic and strength and stiffness degrading ones, are chosen to represent the seismic behavior of typical steel frame and reinforced concrete frame structures. The study may provide useful input towards developing refined guidelines for performance-based seismic design of elevated tanks. [ABSTRACT FROM AUTHOR]