Base-isolated Liquid Storage Tanks Research Articles

Performance of a force-restricted viscous mass damper incorporated into base-isolated liquid storage tanks

Base isolation systems have been widely used to protect large liquid storage tanks (LSTs) from the damaging effect induced by strong earthquake events. In the previous study, viscous mass dampers (VMDs) were incorporated into the isolation layer for suppressing the isolator displacement and liquid sloshing responses of base-isolated LSTs under long-period ground motions. However, it was recently concerned that VMDs may degrade the isolation performance under more commonly occurring short-period ground motions because of their excessive dynamic stiffness and control forces at high frequencies. To address this issue, a modified VMD with a force-restriction mechanism, referred to as force-restricted viscous mass damper (FRVMD), was employed to enhance the seismic performance of base-isolated LSTs. The acceleration and control force transmissibility of the FRVMD controlled system was investigated by using the harmonic balance with alternating frequency/time domain (HB-AFT) method, and compared with the traditional damping devices. A base-isolated benchmark LST model was employed as a numerical example to identify the benefits of FRVMDs in protecting base-isolated LSTs from short- and long-period ground motions, where the result showed that the FRVMD can effectively suppress the isolator displacement and liquid sloshing response of base-isolated LSTs without compromising the base shear. Furthermore, parametric studies were conducted to investigate the influence of aspect ratios, isolation periods, and restriction forces of FRVMDs on the seismic response of the controlled LST. It was suggested that the performance of the FRVMD controlled structure was robust against the variation of aspect ratios and isolation periods.

Negative stiffness and inerter-based dampers: Novel seismic response control approach for base isolated liquid storage tanks

Liquid storage tanks (LSTs) have become indispensable to civil engineering infrastructure. LSTs are used not only for storing harmless fluids but also explosive, toxic, and hazardous substances. Thus, the ability of LSTs to withstand significant seismic activity without damage is a major worry. Strong pulse-type characteristics in near fault (NF) type of ground motions have shown significant base and sloshing displacements for a commonly adopted structural control measure: base isolation (BI). The current study introduces negative stiffness and inerter dampers (NSIDs) as supplemental response control measures to LSTs with BI (BILSTs). Conventional supplemental damping applications in the isolation system are helpful in displacement reduction at the isolator level, but the upper structure response gets severely affected. This study presents NSIDs, characterised by the damping magnification effect, as supplemental dampers to BILSTs. The continuous liquid mass within the tank is represented by discrete lumped masses referred to as sloshing, impulsive, and rigid mass. The stiffness constants of these lumped masses are derived by considering the tank wall and stored liquid physical parameters. The optimal supplemental damping parameters are deduced by developing contour plots describing the sloshing and base displacement response reduction (mitigation) ratios. Through analytical studies conducted using real earthquake records, it has been demonstrated that appropriately designed Negative Stiffness and Inerter Devices (NSIDs) yield enhanced performance for Base Isolated Liquid Storage Tanks (BILSTs). These optimised combinations of NSIDs effectively mitigate isolator displacement, base shear, lumped sloshing mass displacement, and sloshing mass height in response to both near-field (NF) and far-field (FF) base excitations.

Behavior of Base-Isolated Liquid Storage Tanks with Viscous Dampers under Historical Earthquakes Considering Superstructure Flexibility

Liquid storage tanks (LSTs) can be efficiently protected from far-fault earthquakes by base-isolation. However, large isolation system and sloshing displacements may threaten the tank’s safety under near-fault earthquakes. Although the application of supplemental viscous dampers (VDs) at the base-isolation systems of LSTs located in near-fault areas may help, it may also increase superstructure demands under far-fault earthquakes. In addition to the characteristics of the earthquake, the isolation system and the superstructure properties may affect the success of base-isolated LSTs with supplemental VDs. Therefore, a numerical investigation is conducted in this study in order to determine the influence of the supplemental viscous damping ratio, the isolation system period, the tank wall flexibility, and the tank slenderness ratio on the seismic responses of base-isolated cylindrical steel LSTs with supplemental VDs including the base displacement, the sloshing displacement, and the normalized isolation system shear force under both near-fault and far-fault historical earthquake records. The tank is modeled by single-degree-of-freedom systems representing different modes on a common isolation basemat and the nonlinear dynamic analyses are carried out in 3D-BASIS-ME software. Findings show that while supplemental damping is required especially when LSTs with long-period isolation systems are subjected to large magnitude near-fault earthquakes, it may also cause amplifications in the sloshing displacement and isolation system shear force demands in case of far-fault earthquakes. Furthermore, it is determined that the influence of tank flexibility on both the superstructure and the isolation system responses is negligibly small while the tank slenderness ratio may have considerable effects.

Pounding responses of a base-isolated liquid storage tank under bidirectional earthquakes

ABSTRACT The probability of seismic pounding of sliding isolation liquid storage tank (LST) is high. Considering normal impact force and tangential friction force at the location of pounding under bidirectional earthquake, a 3-D calculation model of sliding isolation LST is established based on finite element method. Pounding dynamic responses under unidirectional and bidirectional earthquakes are comparatively investigated, and frequency domain analysis is also conducted. Finally, mitigation measure for adverse effect caused by the pounding is proposed. Results show that the influence of concrete nonlinearity on the pounding is very significant. Dynamic responses are significantly increased due to the pounding, and the maximum tensile stress of tank wall reaches to 2.510MPa under ChiChi earthquake, which exceeds the concrete tensile strength. Besides, pounding causes the high frequency response. Reasonable rubber cushion design can ensure that the maximum displacement of the sliding isolation LST is limited by the moat wall and the failure probability caused by the pounding is decreased.

Effects of Uncertain Soil Parameters on Seismic Responses of Fixed Base and Base-Isolated Liquid Storage Tanks

ABSTRACT Effects of soil-structure interaction (SSI) on the seismic performance of cylindrical ground-supported liquid storage tanks are studied. The present study attempts to investigate the effects of uncertainties, associated with the critical soil parameters, on the seismic behavior of liquid storage tanks. Random multi-layered soil models coupled with the fixed base liquid storage tank are developed and analyzed. Further, the tank structure is considered base-isolated with lead rubber bearing and analyzed with the same set of soil models, to investigate the seismic behavior of base-isolated tank under uncertain soil condition. A set of three ground motions are selected from a large suite through a mean spectral matching scheme for investigating the effect of soil uncertainties on the seismic response. Distributions of the peak seismic response quantities observed herein show that the uncertainties in soil parameters critically affect the seismic responses of fixed base and base-isolated liquid storage tanks. Sloshing displacement of fixed base and base-isolated tanks is affected by both uncertainty in the soil parameters and ground motion characteristics. Nevertheless, for ground-supported tank, relatively larger dispersion or variability of base shear and overturning moment, as compared to that of the sloshing response, is observed.

Vector-Valued Intensity Measures for Seismic Risk Assessment of Base-Isolated Liquid Storage Tanks

The present study proposes vector-valued intensity measures (IMs), consisting of two IM parameters, for improved and efficient seismic risk assessment of liquid storage tanks base isolated with laminated rubber bearing (LRB) and lead rubber bearing or New Zealand base-isolation system (NZ system). To assess the seismic risk of the base-isolated liquid storage tanks, their seismic fragility was obtained using stripe analysis. The joint hazard of the selected IMs was obtained using vector-valued probabilistic seismic hazard analysis. It is shown that the vector-valued intensity measure consisting of peak ground acceleration (PGA) and spectral acceleration (Sa) at the isolation period (Tb) is efficient for predicting the peak base shear demand in the liquid storage tanks base isolated with LRB. Similarly, the vector-valued intensity measure consisting of PGA and peak ground velocity (PGV) is efficient for predicting the peak base shear in the liquid storage tanks base isolated with the NZ system. This study also presents parametric investigations on the effect of thicknesses of the tank wall (tw) and the slenderness ratio (S) of the tank on the seismic risk of the base-isolated liquid storage tanks.

Feasibility analyses of negative-stiffness dampers for seismic performance enhancement of a base-isolated liquid storage tank

Base-isolation systems are widely used to reduce the hydrodynamic base shear and overturning moment of liquid storage tanks with increased isolator displacements and liquid sloshing responses. Supplementing conventional damping devices in the isolation layer can effectively reduce isolator displacements whereas having limited influence on the liquid sloshing. In the present paper, simultaneous reduction on the isolator displacement and sloshing response of a base-isolated liquid storage tank is achieved by using negative-stiffness dampers (NSDs). NSDs consisting of a negative-stiffness component coupled in parallel with a fluid viscous damping component are considered, and an equivalent linearization technique is proposed for designing their properties on the basis of the principle of equal average energy dissipation. A four-lumped-mass model considering high sloshing modes of liquid storage tank is used as a numerical example. The feasibility of NSDs for improving the seismic performance of base-isolated storage tanks with varying aspect ratios is verified. Moreover, nonlinear response history analyses are conducted to illustrate the benefits of the proposed method for the seismic protection of base-isolated storage tanks. The seismic responses of base-isolated storage tanks controlled by using the proposed and traditional methods are comprehensively compared, and it is suggested that the proposed method can be advantageous over conventional ones by more effectively reducing base shear and sloshing responses without compromising isolator displacements.

Elastic and viscous bumpers for seismic mitigation of base-isolated liquid storage tanks in near-fault zones

The use of friction pendulum system (FPS) as a base isolation system is one of the efficient and reliable techniques for seismic response reduction of liquid storage tanks. However, recent studies have shown that the FPS may experience substantial displacements under pulse-like near-fault earthquakes, which could lead to the collision of its articulated slider against the retainer ring. This internal impact in the FPS can make the isolation system less effective or even damaged. The best solution to this problem is to provide an appropriate displacement capacity of the FPS bearing to accommodate the resulting movements. However, due to any practical limitation or under extreme ground motions, the base displacement may exceed the displacement capacity provided and an internal impact may occur. This paper proposes and investigates the use of elastic and viscous bumpers in FPS-isolated tanks subjected to near-fault earthquakes to limit excessive bearing displacements and to prevent direct impact with the retainer. The material properties of the bumpers and their initial gap distance are used as variable parameters in the nonlinear time-history analyses of selected isolated tanks with different aspect ratios. The results, while showing the advantages of viscous bumpers over elastic ones, indicate the effectiveness of both shock absorbers in isolated tanks that are subject to large displacement demands. Based on the results of the parametric study, design recommendations are given for the use of such bumpers in FPS-isolated tanks.

Seismic vulnerability assessment of base isolated liquid storage tanks under near-fault ground motions

This paper aims to develop the fragility curves of base isolated liquid storage tanks under near-fault ground motions. Liquid storage tanks are important lifeline structures for industrial plants, but the damages from the past earthquakes showed their vulnerability. The seismic isolation technique is a promising approach to reduce the seismic demand in liquid storage tanks. It should be considered that near-fault ground motions can damage base-isolated liquid storage tanks due to their characteristics such as pulses in their time history velocity. Therefore, it is important to assess the vulnerability of the liquid storage tanks under near-fault ground motion. Fragility curves are useful tools for structural engineers to evaluate seismic performance of structures. In this study, two types of liquid storage tanks, i.e., broad and slender, are considered. The fragility curves for both non-isolated tanks and base-isolated tanks by Friction Pendulum System are developed and compared. Six failure criteria have been considered for the fragility curves, including vertical displacement of convective mass, elastic buckling of tank wall, yielding of anchorages, elephant foot buckling, pipe-line fracture and base isolation displacement. Furthermore, the effect of the isolation period and the coefficient of friction on the fragility curves are investigated. The results show that the pipeline fracture and the tank’s wall buckling are the two most important parameters, which govern the behaviour of liquid storage tanks.

Improving the seismic performance of base-isolated liquid storage tanks with supplemental linear viscous dampers

Improving the seismic performance of base-isolated liquid storage tanks with supplemental linear viscous dampers

Response and damage evaluation of base-isolated concrete liquid storage tank under seismic excitations

The present study analyzes flexible rectangular concrete base-isolated liquid storage tanks (LSTs) for bi-directional earthquakes. The base-isolated LST is modeled in ABAQUS finite element software. The liquid is modeled by the Equation of State (EoS) with arbitrary Lagrangian-Eulerian (ALE) remeshing algorithm, whereas the hexahedral solid finite elements model LST. Nonlinear time history analysis is performed by considering the LSTs’ material nonlinearity and the nonlinearity produced in LST due to the water-structure interaction. As illustrative examples, different LSTs are considered in the present study with five lead rubber bearing (LRB) isolators each, four at the corners and one at the center. The parameters varied for analysis are the isolators’ effective frequency, peak ground acceleration (PGA), height of water, and aspect ratio of LSTs. The response quantities of interest include Tresca stress, sloshing height, hydrodynamic pressure, overturning moment, and base shear. The numerical study results show that the liquid’s sloshing increases by about 20%–30% at optimum frequency. Still, the forces induced in the tank are considerably reduced. The height of water, and aspect ratio of LSTs significantly influences the response behavior of the isolated tank.

Effects of Soil-Structure Interaction on Seismic Response of Fixed Base and Base Isolated Liquid Storage Tanks

ABSTRACT A detailed numerical framework for seismic analysis of liquid storage tanks considering soil-structure interaction (SSI) is presented. Lumped mass model for the tank and finite element approach for the soil domain are adopted. Effects of SSI on seismic performance of ground supported and elevated liquid storage tanks, with fixed base and base isolated conditions, are studied under near-field and far-field ground motions. Effect of SSI on fixed base tanks is found to be similar under different types of ground motions. Nevertheless, effectiveness of isolation systems with different stiffness characteristics depends on soil type, tank slenderness ratio, and ground motion types.

Performance limits of base-isolated liquid storage tanks with/without supplemental dampers under near-fault earthquakes

In order to ensure the continuity of the production process and avoid health, security, and ecological problems, the protection of the liquid storage tanks (LSTs) in industrial complexes against earthquakes is vital. Although base-isolation is successful in protecting LSTs from the detrimental effects of far-fault earthquakes, it is challenged by large-amplitude and long-period velocity pulses observed in near-fault earthquakes which may cause large isolator and sloshing displacements. Employing supplemental damping in the isolation system may reduce isolator displacements but the improvement in the superstructure response may be limited if not worsened. Thus, determining the performance limits of base-isolated LSTs with/without supplemental damping in terms of both isolation system and superstructure responses through a systematic examination considering different levels of earthquake magnitude and different fault distances is essential. Since the period and the amplitude of the ground velocity pulse is dependent on the earthquake magnitude and the closest fault distance, such an examination will also help reveal the influence of the characteristic properties of near-fault pulses on the responses of these structures. Therefore, here, a benchmark LST with different base-isolation systems with/without supplemental viscous dampers, located at different fault distances are subjected to synthetically generated near-fault earthquake records with different levels of moment magnitudes. Various isolator and viscous damper characteristics are taken into account. Non-linear time history analyses are conducted to obtain isolator displacement, sloshing displacement, and isolation system shear force responses and the performance limits of the benchmark LST with different base-isolation systems with/without supplemental dampers are presented in a comparative manner.

Optimizing the seismic response of base-isolated liquid storage tanks using swarm intelligence algorithms

Large-scale liquid storage tanks are used worldwide for storing water, chemicals and fuels, such as liquefied natural gas (LNG) and oil. Any major damage due to man-made or natural hazards, such as earthquakes, to these critical infrastructures would cause serious socio-economical losses and devastating environmental consequences. Moreover, they should remain functional even after a severe earthquake to support restoration actions, thus, their robust and optimal seismic design is deemed necessary. For this reason, base isolation is generally considered as a highly efficient technique for their seismic protection. Elastomeric bearings, such as lead-rubber bearings (LRB), high damping rubber bearings (HDRB) and friction bearings: single friction pendulum bearings (SFPB), double friction pendulum bearings (DFPB) and triple friction pendulum bearings (TFPB) have been used. In this work, the focus is given on the sizing optimization of the main parameters of SFPB and TFPB isolators. For this reason, efficient swarm intelligence optimization algorithms are used to derive optimal friction coefficient and radius of curvature values that enhance the dynamic performance of a base-isolated liquid storage tank. The main objective of the proposed formulation is to minimize the accelerations transmitted to the superstructure, while constraints related to damping and vibration period of the system are imposed.

Impact of damping modeling on the seismic response of base-isolated liquid storage tanks

Liquid-filled tanks are important infrastructure for the storage of water, chemicals and fuels, such as oil and liquefied natural gas (LNG). Many such large-scale tanks are located in regions with high seismicity. Therefore, very frequently base isolation technology has to be implemented to reduce the dynamic distress of the superstructure. In structural analysis software base isolators are modeled utilizing special nonlinear isolator elements. Global damping modeling of seismically isolated structures is a crucial issue, since improperly defined damping may worsen significantly the dynamic analysis results, mainly due to the so-called "damping leakage" phenomenon. For this purpose, this work is focused on the impact of damping modeling approach in the dynamic response of liquid storage tanks isolated via single friction pendulum bearings (SFPBs) under strong near-fault ground motions.

Seismic Vulnerability Assessment of Liquid Storage Tanks Isolated by Sliding-Based Systems

Liquid-filled tanks are effective storage infrastructure for water, oil, and liquefied natural gas (LNG). Many such large-scale tanks are located in regions with high seismicity. Therefore, very frequently base isolation technology has to be adopted to reduce the dynamic distress of storage tanks, preventing the structure from typical modes of failure, such as elephant-foot buckling, diamond-shaped buckling, and roof damage caused by liquid sloshing. The cost-effective seismic design of base-isolated liquid storage tanks can be achieved by adopting performance-based design (PBD) principles. In this work, the focus is given on sliding-based systems, namely, single friction pendulum bearings (SFPBs), triple friction pendulum bearings (TFPBs), and mainly on the recently developed quintuple friction pendulum bearings (QFPBs). More specifically, the study is focused on the fragility analysis of tanks isolated by sliding-bearings, emphasizing on isolators’ displacements due to near-fault earthquakes. In addition, a surrogate model has been developed for simulating the dynamic response of the superstructure (tank and liquid content) to achieve an optimal balance between computational efficiency and accuracy.

Seismic response of base isolated liquid storage tanks to real and simulated near fault pulse type ground motions

In this paper, the seismic response of base-isolated liquid storage tanks subjected to real and simulated near-fault ground motions is investigated. It is assumed that the tanks are seismically isolated by single surface Concave Sliding Bearings (CSB) with different isolation periods. For the input data, the recorded and simulated ground motions having pulse type characters and their dominant waveforms are considered.For each case considered, numerical analyses are carried out to calculate the critical demand parameters such as base shear values, bearing and sloshing displacements of the tank. The results revealed that, the base shear response of the slender tank to real and simulated ground motions and equivalent pulses tend to approach each other at isolation periods around 3 s and then remain constant in higher periods. Similar findings are not observed for the broad tank. Depending on the special case considered in this study, it can be said that, for the preliminary design of slender tanks in the near-fault regions, the real earthquakes can be replaced by equivalent pulses especially for isolation periods larger than 3s.

Seismic Response of Base Isolated Liquid Storage Tanks under Near Fault Ground Motions

Seismic Response of Base Isolated Liquid Storage Tanks under Near Fault Ground Motions

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

Seismic response of base isolated steel liquid storage tanks is investigated in this study by a stochastic approach in frequency domain. For the purpose of evaluating different frequency contents of seismic events on the responses of fixed and isolated tanks, the earthquake excitation is characterized by power spectral density function. Since earthquake is a random process, stochastic seismic analysis is used and root mean square response predicts behavior of system properly. Two types of isolation system are assumed and nonlinear behavior of base isolation systems are developed by an iterative statistical linearization scheme. The study demonstrates the influence of each characteristic parameter of the storage tanks and isolation system and also excitation features. It is confirmed that near-fault earthquake excitations amplify the overall response of the system. Base isolation is known as an effective technique to reduce responses appropriately. It is demonstrated that the sloshing responses of the tanks is significantly reduced by sliding bearing. Further, excitation parameters, PGV/PGA ratio of records and pulse period in near-fault ground motions, that represent differences in two sets of earthquakes are defined to recognize variation of responses.

Fragility Analysis of Base-Isolated Liquid Storage Tanks under Random Sinusoidal Base Excitation Using Generalized Polynomial Chaos Expansion–Based Simulation

AbstractGeneralized polynomial chaos (gPC) expansion–based simulation technique is used to investigate the influence of input parameter uncertainty, on peak response quantities and fragility curves of base-isolated liquid storage tanks. Unidirectional horizontal sinusoidal base excitation is considered to develop the fragility curves for the base-isolated liquid storage tanks. Extensively used laminated rubber bearing (LRB), with linear force-deformation behavior, is considered as the isolation system. The liquid storage tank is modeled using a widely accepted lumped mass model. The failure of the liquid storage tank is defined corresponding to the elastic buckling of the tank wall. The uncertainties are considered in the isolator parameters and in the base excitation. Considerable difference in the peak response estimation is observed when the input parameters are represented using different probability distributions, especially when the uncertainties are higher. It is also observed that when the uncerta...