Elevated Liquid Storage Tanks Research Articles

Seismic Performance and Control of Elevated Liquid Storage Tanks with Negative Stiffness and Inerter-Based Dampers

Seismic Performance and Control of Elevated Liquid Storage Tanks with Negative Stiffness and Inerter-Based Dampers

Seismic behaviour of elevated liquid storage tanks by considering the different soil types using MATLAB software

For a structure the soil structure interaction (SSI) is the connection between the super structure and the foundation. In this paper, the seismic responses of liquid storage elevated tank with SSI and without SSI effects are considered and effects were analysed. The consequences of SSI on peak seismic responses of tank like displacement, overturning moments are discussed. Furthermore, the impacts of different factors such as slenderness ratio and time period of liquid tank staging on the seismic performance of the raised tank are investigated. From the study it is observed that the soft soil is prone to overturning moment of water storage tank and also found that as the slenderness increases, the overturning moment decreases gradually irrespective of soil type and time period of the staging.

Nonlinear Seismic Analysis of RC Elevated Liquid Storage Tanks

Liquid storage tanks are strategically important due to their essential requirement of service in the post-earthquake situation. Numerical modeling of the liquid storage tank needs special attention and cannot be done in the same manner as that of the conventional buildings. In the present paper, a numerical simulation of the RC elevated liquid storage tank is presented. The staging of the tank is modeled as a multi-degree freedom system, and the container with contained liquid is modeled as a two-mass system. Free vibration analysis of the tank is carried out, and mode shapes are extracted. Further, to study the seismic response of the tank, nonlinear time history analysis is carried out. The tank is subjected to time histories of real earthquake ground motions. The varying level of the liquid in the container is another characteristic feature of tanks. The filled condition of the tank is taken into account by considering the aspect ratio (S), defined as the ratio of height of the liquid to the radius of the container. The response of the tanks with two different aspect ratios viz. 0.5 (broad) and 2.0 (slender) is studied. The linear modal analysis also carried out to understand the significance of nonlinear analysis, particularly in liquid storage tanks. Displacement, velocity, and acceleration response at the bracing levels, as well as at container levels, are obtained. Additionally, the base shear response is also obtained. The effect of aspect ratio on the free vibration analysis and the seismic response of the tanks are presented. Liquid storage tanks are special structures that have typically low fundamental natural frequencies. The nonlinear time history response of the tank showed that the higher displacement and velocity response occurs at the convective level. It is found that the linear modal analysis significantly underestimates the response of the liquid storage tank.

Performance of RC elevated liquid storage tanks installed with semi‐active pseudo‐negative stiffness dampers

The effect of semi-active pseudo-negative stiffness dampers (SAPNSDs) on the seismic response mitigation in the reinforced concrete (RC) elevated liquid storage tanks is investigated. The SAPNSDs are operated in two modes: Passive-ON and Passive-OFF. The effect of placement (location) of the dampers is also studied by placing the dampers in three different configurations. Two aspect ratios of the tanks, viz., 0.5 and 2.0, are considered to study the effect of the variable level of the liquid in the container. Time history analysis is carried out for total of 18 different earthquake ground motions. The differential equations of motion are solved by the state-space approach. The response quantities such as peak base shear, overturning moment, container level displacements, and bracing level displacements, along with the damper forces, are obtained. It is found that the SAPNSDs (Passive-ON) effectively control the response of the RC elevated liquid storage tanks. Further, seismic energy input to the structure without SAPNSDs and the percentage energy dissipated by SAPNSDs is obtained. The placement of the dampers plays a significant role in response reduction during ground motion with high peak ground acceleration (PGA) than that with low PGA. The SAPNSDs installed at alternate levels (Configuration II) is the most efficient configuration for response control of the RC elevated liquid storage tank installed with the SAPNSDs. The seismic input energy reduces considerably by the installation of the semi-active pseudo-negative stiffness dampers (SAPNSDs).

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.

Influence of Nonlinear Fluid Viscous Dampers on Seismic Response of RC Elevated Storage Tanks

The numerical investigation on the seismic response of RC elevated liquid storage tanks installed with viscous dampers is presented. A discrete two-mass model for the liquid and multi-degree of freedom system for staging, installed with the dampers are developed for Reinforced Concrete (RC) elevated liquid storage tanks. The elevated tank is assessed for seismic response reduction when provided with Linear Viscous Damper (LVD) and Nonlinear Viscous Damper (NLVD), installed in the staging. The RC elevated liquid storage tanks are analyzed for two levels of liquid containment in the tank, 100% and 25% of the tank capacity. Three Configurations of placements of dampers viz. dampers at alternate levels (Configuration I and Configuration II) and dampers at all the panels of the staging of the tank (Configuration III) are considered. To study the effect of peak ground acceleration, eight real earthquake time histories with accelerations varying from 0.1 g to 0.93 g are considered. The nonlinearity in the viscous damper is modified by taking force proportional to various velocity exponents. It is found that the nonlinear viscous dampers with lower damping constant result in a comparable reduction in the response of RC elevated liquid storage tank, to that of linear viscous dampers with higher damping constant. A lower damping constant signifies compact the size of the damper. Doi: 10.28991/cej-2020-SP(EMCE)-09 Full Text: PDF

Seismic Performance of Base-Isolated Elevated Liquid Storage Tanks Considering Soil–Structure Interaction

AbstractSeismic performance of elevated liquid storage tanks, considering soil–structure interaction (SSI), is investigated. The effects of considering SSI on the peak seismic responses, as well as...

Semi-Active Fluid Viscous Dampers for Seismic Mitigation of RC Elevated Liquid Storage Tanks

The effectiveness of the semi-active control strategies using fluid viscous dampers (SAFVDs) for seismic mitigation of reinforced concrete (RC) elevated liquid storage tanks is investigated. Three control algorithms are employed for regulating the damping coefficient of the SAFVDs: (1) Passive-OFF, (2) Passive-ON, and (3) Clipped Optimal Control (COC). The uncontrolled response of the tank is compared with those installed with SAFVD of different control algorithms. Focus is also placed on various positions of the dampers, viz., dampers installed at alternate levels (Configurations I, II, IV, and V) and at all levels (Configurations III and VI) of the staging. A discrete two-mass model for the liquid and multi-degree-of-freedom system for the staging, installed with the dampers, is developed for the RC elevated liquid storage tanks. The response of the broad and slender tanks is studied, for which the ratios of the height of the liquid to the radius of the container are 0.5 and 2.0, respectively. The time-history response of the elevated tank is evaluated for eight different earthquake ground motions, including near- and far-field earthquakes. A MATLAB code was developed to solve the coupled differential equations of motion of the system using the state-space approach. Key parameters, viz., convective displacement, rigid mass displacement, base shear, overturning moment, and damper force, are evaluated. The results show that all the control systems considered herein are beneficial in reducing the seismic responses. The frequency response function for the uncontrolled and semi-actively controlled liquid storage tank in frequency domain exhibits significant response reduction, highlighting the effectiveness of the SAFVDs. The structural response is effectively controlled using the SAFVDs with Passive-OFF (valve closed) and COC algorithms. The COC algorithm employed in this study is a promising candidate for the seismic mitigation of RC elevated liquid storage tanks using the semi-active control.

RESPUESTA SÍSMICA DE TANQUES ELEVADOS TIPO PÉNDULO INVERTIDO

La mayoría de los tanques elevados para el almacenamiento de líquido son considerados como estructuras que forman parte de instalaciones vitales ya que deben permanecer funcionando correctamente aún después de la ocurrencia de un sismo. Los tanques elevados difieren de los tanques apoyados sobre el terreno debido a que están formados por dos partes: el elemento de apoyo y el contenedor. En décadas pasadas se han presentado numerosas fallas en este tipo de estructuras debidas a eventos sísmicos. En este artículo se plantea la ecuación general de movimiento de un tanque elevado considerando el modelo simplificado masa-resorte para modelar el líquido contenido en el tanque con paredes rígidas y la posibilidad de que se presente rotación en la base del contenedor. Los resultados indican la importancia de considerar en la ecuación de movimiento al menos tres modos convectivos del líquido, principalmente en la zona del Valle de México, además de la importancia de no despreciar la contribución de la rotación de la base del contenedor en el cálculo del momento en la cimentación del tanque.

Passive energy dissipation-based retrofit strategies for R/C frame water towers

Pre-normative elevated liquid storage tanks with reinforced concrete (R/C) frame staging are among the most seismically vulnerable structures in urban areas, due to their unfavourable earthquake-resistant configuration. A representative case study, i.e. a R/C water tower designed by the world-famous Italian engineer Pier Luigi Nervi and built in the early 1930s, is examined herein. The assessment of the structure was developed with a detailed finite element model, which includes a multi spring-mass assembly to reproduce the fluid–tank dynamic interaction. The time-history evaluation analysis, initially carried out by assuming an elastic behavior of the staging members, showed general unsafe response conditions of beams and columns under seismic action scaled at the maximum considered earthquake (MCE) level. These results were confirmed at a second step of the analysis, where the plastic behavior of beams and columns was investigated after incorporating lumped plastic hinges at their end sections, which resulted in the collapse of the model. Based on these data, two passive energy dissipation-based retrofit measures were proposed, for which dissipative bracing systems incorporating either pressurized fluid viscous spring-dampers or added damping and stiffness steel yielding devices, respectively, were installed. The two systems were designed with a mutual energy-based criterion and for the same target performance objectives, that is, reaching elastic response up to the MCE. The benefits induced by the two protective systems to the seismic response of the tank structure are discussed, and the geometrical dimensions and relevant architectural impact are compared with the ones of a conventional non-dissipative bracing retrofit solution developed for the same performance.

Seismic Response of Elevated Liquid Storage Tanks Using Double Concave Friction Pendulum Bearings with Tri-Linear Behavior

In the current paper, the seismic response of elevated liquid storage tanks using double concave friction pendulum bearings (DCFP) considering bi-linear and tri-linear behaviors have been investigated. After deriving the coupled differential equations of motion, the MATLAB programming language is employed to solve the differential equations in each time step in order to obtain the time history response of isolated tank under near fault ground motions. The advantages and disadvantages of tri-linear behavior over bi-linear one on the response of isolated tanks is scrutinized by studying the effects of main parameters such as isolation period, tank period with fixed base, tank aspect ratio and base mass ratio on the tank response. It is demonstrated that change in bearing behavior form bi-linear to tri-linear dramatically affects the bearing maximum displacement while the peak value of other parameters such as sloshing displacement or tower shear force may experience less variations.

Comparative Performance of Elevated Isolated Liquid Storage Tanks (With Shaft Staging)

Liquid storage tanks are important components of lifeline and industrial facilities. They are critical elements in water supply scheme and fire fighting system, and extensively used for storage and processing of variety of liquid like material such as petroleum product, liquefied natural gas, chemical fluid and wastage of different forms. In this paper, the seismic response of base isolated cylindrical liquid storage tanks is investigated under real earthquake ground motion. The isolation systems considered is elastomeric bearings (without lead core), the specific objectives of the study are to carry out the comparative performance of the tanks with isolation and without isolation (i.e. Fixed tanks) also to investigate the response of the tanks for varying capacity with varying heights. For this study forty tanks of varying heights such as 8m,10m,11m,11.5m,12.5m,14m,16m with varying capacities of 500kl,265kl,200kl,100kl,50kl are considered. For this a time history analysis has been carried out by using a three time history of varying magnitude with varying peak ground acceleration. It is observed that the base shear of elevated liquid storage tanks supported on shaft is significantly reduced due to isolation. The drift of the tank relation to base of shaft is also significantly reduced due to isolation. The earthquake response of isolated short tanks is relatively more, i.e. Isolation is not effective for stiffer shafts, and however in general, the effectiveness of base isolation is achieved for tall tanks. Although the effectiveness of seismic isolation increases with the increase of bearing flexibility and damping these properties needs to be modified for desired response.

Seismic analysis and modeling of isolated elevated liquid storage tanks

In this paper, the seismic response of elevated broad and slender liquid storage tanks isolated by elastomeric or sliding bearings was investigated. The accuracy of predictions of SAP2000 vs. 3D-BASIS-ME programs was examined. A comparative study of the performance of base isolated tanks when isolation bearings are placed at the top or at the bottom of the supporting tower structure was conducted. It was found that base isolation is quite effective in reducing the earthquake response of elevated liquid storage tanks in which high reductions of base shear and shaft displacement were achieved. Modeling the isolated tanks in SAP2000 was very successful in producing results that are nearly identical to those of program 3D-BASIS-ME. Placing the isolators at the top of the shaft in elevated tanks proved to be much better than placing them at the bottom.

The seismic response of elevated liquid storage tanks isolated by lead-rubber bearings

The seismic response of elevated liquid storage tanks isolated by the lead-rubber bearing is investigated under real earthquake ground motion. Two types of isolated tank models are considered in which the bearings are placed at the base and top of the tower structure. The tank liquid is modelled as lumped masses referred as convective mass, impulsive mass and rigid mass. The corresponding stiffness associated with these lumped masses has been worked out using the properties of the tank wall and liquid mass based on simple single-degree-of-freedom concepts. The mass of the tower structure is lumped equally at top and bottom. The assembled equations of motion are solved by Newmark's step-by-step method with iteration. The seismic response of two types of tanks, namely slender and broad tanks is obtained and a parametric study is carried out to study the effects of important system parameters on the effectiveness of seismic isolation. The various important parameters considered are the tank aspect ratio, the time period of the tower structure, damping and the lime period of the isolation system. It has been observed that the earthquake response of the isolated tank is reduced significantly. Further, it is observed that the isolation is more effective for the tank with a stiff tower structure in comparison to flexible towers. In addition, a simplified analysis is also presented to evaluate the response of the elevated tanks using a two-degrees-of-freedom model and two single degree-of-freedom models. It is observed that the proposed methods predict accurately the seismic response of elevated liquid storage tanks with less computational efforts.

Seismically Induced Fluid Forces on Elevated Tanks

Seismically induced fluid forces on elevated liquid storage tanks and their supporting systems are evaluated. X-braced as well as pedestal towers are analyzed. The interaction between liquid sloshing modes, tank rotation, tank translation and tank wall flexibility is taken into consideration to assess the relative importance of such effects on the overall earthquake response of elevated tanks. Ideal liquids and elastic towers are assumed throughout the first phase of the study. A comparison between the calculated forces and those provided by applicable codes is made.