CONFIRMATION OF REDUCTION EFFECT DUE TO TANK'S ROCKING BEHAVIOR AND PROPOSAL FOR A SIMPLIFIED EVALUATION METHOD OF NONLINEAR SEISMIC RESPONSE

摘要

Aboveground LNG storage tank consists of inner and outer cylindrical containers. LNG is stored in the inner container made by 9%Ni steel. Anchorages are attached to some tanks in order to prevent bottom plate from excessive uplifting by seismic overturning moment. However tanks without anchorages have some probability that the seismic response factor decreases since the resonance period of tank is lengthened by nonlinear behaviors, for example uplifting of bottom plate (rocking behavior). In this paper, the reduction effect of response factor due to rocking behavior was quantitatively confirmed by 3-dimensional FEM nonlinear analysis and time-history nonlinear analysis that was modeled with single-degree-of-freedom spring-mass system. And a simplified evaluation method that allows easily calculating the reduction effect was proposed. As the result of study, it was proved that this method gave valid and conservative results.