INVESTIGATION OF STRESS REDUCTION EFFECT ON STRUCTURES DUE TO BASEMAT UPLIFT USING ENERGY CONCEPT

Abstract

This paper studies stress reduction effects induced on structures (such as bridge piers) due to
basemat uplift and soil yielding by the use of a macro-element model for foundations placed on sand. A
foundation-soil system is modeled as four cases; (1) fixed base, (2) elastic soil, (3) elastic soil with basemat
uplift and (4) elasto-plastic soil with basemat uplift. Time histories with different frequency characteristics
are considered as input motions to the models. Comparisons of responses of the models show a remarkable
reduction of section force due to basemat uplift and soil yielding, depending on characteristics of input
motions. Regarding the case where degree of stress reduction effect is largest, energy balance for the system
is estimated. In this case, the input energy imparted to the structure by an earthquake tends to be reduced due
to the effect of basemat uplift.