Seismic response of liquid storage steel tanks with variable frequency pendulum isolator

Abstract

The seismic response of liquid storage steel tanks (slender and broad) isolated with Variable Frequency Pendulum Isolators (VFPIs) is investigated under normal component of six near-fault ground motions. The continuous liquid mass is lumped as convective mass, impulsive mass and rigid mass. The corresponding stiffness associated with these lumped masses is worked out depending upon the properties of the tank wall and liquid mass. The frictional forces mobilized at the interface of the VFPI are assumed to be velocity independent. The governing equations of motion of liquid storage steel tanks isolated with the VFPIs are derived and solved in the incremental form using Newmark's step-by-step method assuming linear variation of acceleration over small time interval. For comparative study, the seismic response of liquid storage steel tanks with the VFPIs is compared with that of the same liquid storage steel tanks isolated using the Friction Pendulum Systems (FPSs). In order to measure the effectiveness of isolation system, the seismic response of isolated steel tanks is compared with that of the non-isolated steel tanks. Further, a parametric study has been carried out to critically examine the behaviour of liquid storage steel tanks isolated with VFPIs. The important parameters considered are the friction coefficient of the VFPI, the Frequency Variation Factor (FVF) of the VFPI and the tank aspect ratio. The difference between the liquid storage tanks isolated with the VFPI and the FPS isolators subjected to the harmonic and far-field ground motions was also investigated in this study. Effect of vertical component of ground motions on the behaviour of the VFPI-isolated liquid storage tanks is investigated under triaxial ground excitations by considering the interaction of forces in two orthogonal directions. From these investigations, it is concluded that seismic response, viz. the base shear, the sloshing displacement and the impulsive displacement, of liquid storage steel tanks during near-fault ground motions can be controlled within a desirable range with the installation of the VFPI. Under strong harmonic excitations, the base shear of the VFPI reduces than that of the FPS whereas the sloshing displacement, the impulsive displacement and the isolator displacement of the VFPI exceeds than that of the FPS. It is also found that the isolation by the FPS and VFPI isolators has almost the same effect in the tank to the far-field ground motions. The triaxial ground motions have noticeable effect on the response of the VFPI-isolated liquid storage tanks relative to unilateral ground motion and if ignored, the sliding displacement and base shear will be underestimated.

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Pounding Dynamic Responses of Sliding Base-Isolated Rectangular Liquid-Storage Structure considering Soil-Structure Interactions

“…One of the main shock absorption measures is rubber isolation, which can reduce dynamic responses, such as base shear, overturning moment, and wall internal force, of the liquid-storage structure, but its effect on liquid sloshing is very limited and may even produce the opposite effect [1][2][3][4]. However, some new types of sliding isolation methods can achieve independence of the isolation period and liquid sloshing period [5] and avoid the resonance phenomenon, which can reduce both the structural dynamic responses and liquid sloshing simultaneously [6,7]. Therefore, if this design is reasonable, the effect of this sliding base-isolated technology will be better than rubber base isolation [8,9].…”

Parametric study of stochastic seismic responses of base-isolated liquid storage tanks under near-fault and far-fault ground motions

“…Considering near and far fault earthquakes Soni et al. (2011) and Panchal and Jangid (2011) analyzed isolated liquid storage tanks with pendulum systems. Curadelli (2013) introduced an equivalent linear stochastic seismic analysis and provided some guidelines for preliminary design of isolated tanks.…”