Civil Engineering Association

SEISMIC RESPONSE OF UNANCHORED CYLINDRICAL LIQUID-TANK SYSTEMS

The "uplift mecbanismn, developed in response to large overtuniing moment, is the dominant response behaviour of unanchored liquid-tank systems under seismic load. Associated wi t h the base plate uplift , significant deformation and intensive stresses are developed in the tank structure. intense iiquid motion, both the impulsive and the convective component, is also induced fiom the coupling effect. The uplift mechanism is highly nonlinear. Its significance and mechanism in contributing to the seismic behaviour is not fully understood. In this thesis, the seismic behaviour time history of an unanchored broad liquid- tank system is analyzed with the focus on the uplift mechanism. The 1940 El Centro
and the 1994 Northridge earthquakes are used as the ground excitations. The up- lift phenomenon of the base plate, its effects on the shell wall deformation and the dynamic characteristics of the liquid-tank system are studied. The liquid motion developed in the partially uplifted liquid- tank system and the corresponding hydro- dynamic loads are analyzed. The intensive stress developed in the tank structure and the failure mechanism are discussed. A parametric study is conducted to define the effects of the properties of the liquid-tank system on the uplift rnechanism. The seismic behaviour tirne history of mode1 liquid-tank systems with variant structural stiffness and liquid height to tank radius ratio are studied. By varying these parameters, the uplift behaviour, liquid motion and structural stress of the liquid-tank system are carefully compared 2nd deterrnined.