Seismic Isolation of Liquefied Natural Gas Tanks: a Compartive Assessment

In severe seismic environments, tanks for storage of liquefied natural gas may benefit from seismic isolation. As the design accelerations increase, the inner tank undergoes progressively greater demands and may suffer from corner uplift, elephant’s foot buckling, gross sliding, shell thickness requirements beyond what can be reliably welded and, eventually, global uplift. Some of these problems cause extra costs while others make the construction impossible. The seismic environments at which the previous problems arise are quantified for modern 160,000 m3 tanks, whether supported on shallow or pile foundations, for both a conventional design and one employing seismic isolation. Additionally, by introducing some cost assumptions, comparisons can be made as to the cost of dealing with the seismic threat for each seismic environment and tank design option. It then becomes possible to establish the seismic environments that require seismic isolation, as well as to offer guidance for decisions in intermediate cases

Analysis and Design Procedure for Liquid-Filled Conical Tanks Under Seismic Loading

Steel conical tanks are widely used for liquid storage in North America and elsewhere. A number of those tanks collapsed in the last decades as a result of instability of the steel shells. Despite being widely used, no specific design procedure is available for conical tanks under dynamic conditions. The research conducted in the current thesis presents a simplified approach for the design of steel conical tanks when subjected to ground excitations in the form of horizontal and vertical excitations. First, the capacity of steel conical tanks to avoid yielding and buckling of the tank vessel under hydrodynamic pressure resulting from horizontal ground excitation is evaluated using non-linear static pushover analysis. The capacity of steel conical tanks under hydrodynamic pressure resulting from vertical ground excitation is then evaluated using the same procedure. The analyses are conducted numerically using a non-linear finite element model that accounts for the effects of large deformations and geometric imperfections on the stability of steel conical tanks. Based on the obtained capacities, a design approach is proposed which is based on satisfying an interaction formula that avoids both yielding and buckling of the tank vessel. This formula is a function of the steel conical tank capacities and the seismic demands resulting from hydrodynamic pressure including both impulsive and sloshing components. Finally, this design approach is validated through comparison with the results of non-linear dynamic analysis. The effect of the base rocking motion on the seismic behaviour of conical shaped steel tanks is then studied and a mechanical analog that simulates the forces acting on a conical tank subjected to a horizontal excitation including the effect of this base rocking motion is developed. This mechanical model takes the flexibility of the tank walls into consideration as well the hydrodynamic pressure acting on the tank base

Effect of MetaFoundation on the seismic responses of liquid storage tanks

Cylindrical liquid storage tanks are vital lifeline structures, playing a critical role in industry and human life. Damages to these structures during previous earthquakes indicate their vulnerability against seismic events. A novel strategy to reduce the seismic demands in the structures is the use of metamaterials, being periodically placed in the foundation, called MetaFoundation (MF). The periodic configuration of metamaterials can create a stop band, leading to a decrease in wave propagation in the foundation. The aim of this paper is to study the effect of MF on the dynamic behaviour of liquid storage tanks. To that end, the governing equations of motion of the liquid storage tank equipped with MF are derived and solved in the time domain to obtain the time history of the responses under a set of ground motions. Then, the peak responses of tanks, mounted on MF, are compared with the corresponding responses in the fixed base condition. Besides, a parametric study is performed to assess the effect of the predominant frequency of earthquakes, the number of layers of metamaterials, the thickness of soft material, and the damping ratios of soft material on the performance of the MF. The obtained results indicate that the MF improves the dynamic behaviour of the squat tank, in which the mean ratio of responses using MF to the ones in the fixed base conditions equals 0.551 for impulsive displacement, overturning moment, and base shear

Parametric study on dynamic behavior of rectangular concrete storage tanks

Tanks are used to store a wide variety of liquids such as oil, gasoline and water. It is reported that, a large number of tanks have been damaged during severe earthquakes. Therefore, understanding their behavior under earthquake is an important subject for structural engineers. In this paper, a comprehensive study is presented on dynamic response of tanks. A parametric study has been completed on the rectangular storage tanks with aid of finite element method (FEM). Various parameters are investigated, such as; liquid height, density and earthquake with different peak ground acceleration (PGA). When investigating these parameters, modal and time history method is used. Six different earthquake records are used for time history analysis. The analysis results show that when the PGA increases by 10.7 times, the maximum displacements, stress, sloshing and base shear increase by 11.4, 22.6, 5.46 and 17.8 times, respectively and when the liquid height increases by two times, the absolute maximum values of stress, displacements, base shear and sloshing increase 1.65, 2.04, 2.05 and 1.34. Furthermore, values of sloshing increase with decrease in density

Three-Dimensional Nonlinear Dynamic Analysis of Base Isolated Cylindrical Steel Tank

Failure of a tank during an earthquake can result in significant financial, human, and environmental losses. Thus, their lack of resiliency against strong earthquakes may result in refinery disruption. This has the potential to have a considerable impact on any economic system. As a result, more research into the seismic performance of tank structures is required to attain the highest possible level of resistance against strong earthquakes. In this paper, we aim to look into the installation of seismic isolation systems in cylindrical steel storage tanks. A nonlinear 3D finite element model is developed with ANSYS software. Moreover, tank wall material nonlinearity, fluid-structure-interaction, and sloshing components are considered. The bilinear hysteretic LRB is used for modal and time-history analysis. In this work, three tanks with varying aspect ratios are studied: "Model A", "Model B", and "Model C". Furthermore, the fixed tank's fundamental frequencies were compared to the analytical results of the American API 650 Standard. Subsequently, the dynamic behavior response of the researched tanks to the horizontal component of the El-Centro 1940 earthquake with PGAs of 0.34g and 0.5g is investigated. As a result, the dominating frequency of the seismic isolation system is within the effective frequency range of seismically isolated systems. The results illustrate that the base isolation limits the tank wall movement with a large displacement in the isolators; the mode shape is a cantilever beam in all isolated circumstances. The total seismic response reduction in the slender tanks is greater as compared to the broad case in the base-isolated tanks. The sloshing displacement increases with an increase in the tank aspect ratio. Additionally, the isolation device eliminates tank buckling at the base and top of the tank shell during seismic excitation (elephant foot and diamond buckling). It can be concluded that the seismic isolation technique has a more significant impact on reducing the dynamic response of ground-supported tanks, particularly in taller tanks as compared to broad tanks. Doi: 10.28991/CEJ-2022-08-06-013 Full Text: PD

Seismic analysis and strengthening of cylindrical steel storage water tanks

Silindirik çelik sıvı tankları su, petrol ve endüstriyel kimyasallar gibi çeşitli sıvıları depolamak amacıyla yaygın olarak kullanılmaktadırlar. Sıvı depolama tankları birçok farklı konfigürasyona sahiptirler; ancak bu çalışmada, tasarım ve konstrüksiyondaki sadelikleri ve diğer konfigürasyonlarla karşılaştırıldığında hidrostatik ve hidrodinamik yüklere karşı dayanımlarından dolayı, yerden destekli silindirik sıvı çelik tanklar tercih edilmektedir. Bu tez, yerden destekli silindirik (dikey) çelik su depolama tanklarının sismik tasarımına odaklanmaktadır. Üç boyutlu sonlu elemanlar analizi için, ANSIS Workbench yazılımı ile üstü-açık, düz-kapalı, konik-kapalı ve üstü-kubbe şeklinde kapatılmış tank modelleri tasarlanmıştır. Sismik analiz, El-Centro ve Kobe deprem yükleri altında dört farklı kapak şekline sahip, üç farklı duvar kalınlığındaki tanklar ile gerçekleştirilerek, eksenel deformasyon, eşdeğer gerilme ve burkulma sonuçları sırasıyla hem impulsif hem de konvektif kütleler için sunulmuştur. Sonuçlar, eksenel deformasyonun, konik ve kubbeli tanklarda ciddi şekilde azaldığını göstermektedir. Öte yandan, düz kapatılmış tankların hiçbir avantajının olmadığı görülmüştür. Duvar kalınlığı arttırıldığında, düz kapalı tanklarda eksenel deformasyonun azalmadığı ve düz çatı üzerinde bu deformasyon ve burkulmanın meydana geldiği gözlemlenmiştir. Bu tezin önemli amaçlarından biri de, silindirik çelik sıvı depolama tanklarının güçlendirilmesidir. Gerilmeleri ve burkulmaları azaltmak için tanklara epoksi-karbon sarılmıştır. Sonlu elemanlar metodu kullanılarak epoksi-karbon ile sarılmış tanklarda eksenel deformasyonun azaldığı görülmüştür. 4 mm kalınlığındaki bir tankın 6 mm kalınlığındaki korunmamış bir tanktan daha iyi bir performansa sahip olabileceği vurgulanarak, epoksi-karbon tankların güçlendirilmesi için öneriler getirilmiştir. Son olarak, kısa deprem yükü altında gerçekleştirilen etki analizi ile, tank duvarlarında meydana gelen plastik deformasyonları görebilmek için 0,22 saniyelik El-Centro deprem kaydı, deplasman kaydı olarak kullanılmıştır. Bu analiz sonucunda depremlerde meydana gelmiş burkulma şekillerine benzer sonuçlar ortaya çıkarılmıştır

Seismic Response of Tanks and Vibration Control of their Pipelines

The purpose of this work is to detail some methodologies applied for analysis of the seismic behaviour of existing bottom supported storage tanks and pipelines, under predominantly horizontal seismic actions. Developments on the established finite element method (FEM), permitted to analyse tanks and their liquid contents by two possible approaches: Ritz method coupled with FEM applied to an analytical solution of the tank-liquid system; FEM of the full system by modelling the liquid as a degenerated solid. Both formulations permit to determine seismic response envelopes. Further, some considerations on active control of cylinders by piezoceramic stacks of actuators are outlined, for potential uses in pipelines and tube-like structures

Predicting Dynamic Capacity Curve of Elevated Water Tanks: A Pushover Procedure

Despite the importance of water tanks for water supplies and supporting the community resilience through the firefighting usages in catastrophic conditions, post-earthquake situations especially, a few studies have been done on seismic behavior of water tanks so far. The scope of this paper is to propose a new pushover procedure to evaluate seismic responses of elevated water tanks (EWT) supported on the concrete shaft in the form of dynamic capacity curves (i.e. base shear versus top displacement). In this regard, a series of shaft supported EWTs are simulated considering soil-structure and fluid-structure interactions. The shaft is modelled with frame elements and plastic hinges are assigned along the shaft to consider the material nonlinearity. The effect of soil-structure interaction and fluid-structure interaction are considered through the well-known Cone model and modified Housner model, respectively. At first, parametric studies have been conducted to investigate the effects of various essential parameters such as soil type, water level and tank capacity on seismic responses of EWTs using incremental dynamic analysis (i.e. nonlinear-time-history-analyses with varying intensities). Thereafter, pushover analyses as nonlinear static analyses are performed by variation of lateral load patterns. Finally, utilizing these results and comparing them with mean IDA curve, as an exact solution; a pushover procedure based on the most reliable lateral load patterns is proposed to predict the mean IDA curve of the EWTs supported on the concrete shaft. The obtained results demonstrate the accuracy of the proposed pushover procedure with errors limited to 30 % only in the changing stage from linear to nonlinear sections of the IDA curve

Seismic behavior of a low-rise horizontal cylindrical tank

Abstract Cylindrical storage tanks are widely used for various types of liquids, including hazardous contents, thus requiring suitable and careful design for seismic actions. The study herein presented deals with the dynamic analysis of a ground-based horizontal cylindrical tank containing butane and with its safety verification. The analyses are based on a detailed finite element (FE) model; a simplified one-degree-of-freedom idealization is also set up and used for verification of the FE results. Particular attention is paid to sloshing and asynchronous seismic input effects. Sloshing effects are investigated according to the current literature state of the art. An efficient methodology based on an "impulsive-convective" decomposition of the container-fluid motion is adopted for the calculation of the seismic force. The effects of asynchronous ground motion are studied by suitable pseudo-static analyses. Comparison between seismic action effects, obtained with and without consideration of sloshing and asynchronous seismic input, shows a rather important influence of these conditions on the final results