Effect of Base Uplift on Dynamic Response of SDOF Structures

Abstract

The effect of base uplift on the maximum response of single‐degree‐of‐freedom (SDOF) structures is examined in this paper. A parametric investigation performed for the case of a rigid foundation and a harmonic excitation shows that the maximum deformation is greatly affected by the ratio of the period of the structure to the period of the excitation, while the effects of the amplitude of the excitation, the slenderness of the structure, and its damping are much less. Based on these results an empirical formula for the estimation of the peak response is established. Using this formula and the classical response spectrum, derived for the fixed‐base system, an approximate method is proposed for the estimation of the maximum earthquake deformation with base uplift. The simplified method can also be applied to the case of a flexible foundation, under certain substitutions, based on the classical theory of soil‐structure interaction. Using modal decomposition, the response of multi‐degree‐of‐freedom systems can also be predicted. The results show that uplift is beneficial to the structure for a wide range of natural periods but leads to a larger response for short periods.