Open-topped Tanks Research Articles

Proposition of economic ring-stiffener cross-section to meet the requirements of wind-buckling stability of open-top cylindrical tank

Proposition of economic ring-stiffener cross-section to meet the requirements of wind-buckling stability of open-top cylindrical tank

Stability response assessment of steel thin-walled open-top tanks subjected to local support edge settlement

Purpose Vertical cylindrical welded steel tanks are typical thin-walled structures that are very susceptible to buckling under settlement. The major concern in the design of these thin-walled structures is buckling failure. On this basis and by considering the findings of the previously reported research works, the stability performance of open-top steel tanks with various industrial applications under local support edge settlement is further investigated in this paper. This study aims to contribute to the current state-of-the-art in the design and retrofit of such thin-walled structures. Design/methodology/approach The buckling behaviors of numerous cylindrical shell models with various height-to-radius, radius-to-thickness and settlement span ratios are investigated through linear and nonlinear buckling analyses. The effects of addition of a top stiffening ring on the buckling behavior of cylindrical steel tanks are studied as well. Findings This parametric study demonstrates that the choice of the height-to-radius, radius-to-thickness and settlement span ratios as well as addition of the top stiffening ring can be quite effective on the stiffness and strength performances, deformations and stress distribution as well as intensity of vertical cylindrical welded steel tanks subjected to local support edge settlement. Originality/value This research endeavor was formulated on the basis of a comprehensive literature survey and demonstrates the relationship between geometrical as well as stiffening features and buckling stability performance of open-top tanks subjected to local support edge settlement and also provides practical recommendations for design and retrofit purposes.

Experimental study on the wind-induced buckling of open-top storage tanks with wind girders via 3D-DIC technique

Large open-top storage tanks are susceptible to buckling failure under the combination of external and internal wind pressures. Therefore, wind girders are recommended to be installed on the tank wall to improve its buckling capacity. Most previous experiments on buckling of cylindrical shells typically measured the response at a certain point with a single displacement sensor, and the buckling modes are not readily available. In this study, a measurement technique based on the three-dimensional digital image correlation method is utilized to analyze the buckling behavior of several elastic tank models with aspect ratios of 0.5 and 0.2 in the boundary layer turbulence. The critical buckling pressure and instantaneous displacement field on the windward side of models with and without wind girders are presented and compared with the results of finite element analysis. In addition, the effects of wind girders and imperfections are further discussed. The results indicate that the deformation of the tank wall can change the wind pressure, making it more difficult to return to the pre-buckling state. The wind girders can significantly restrain the buckling deformation and increase the critical buckling load. However, as the wind girders become rigid, the strengthening effect becomes almost constant, and the stiffened tanks are more sensitive to initial geometric imperfections. Based on the cylindrical shell buckling theory and existing calculation methods, an empirical formula for the critical buckling wind pressure of open-top storage tanks with different numbers of wind girders in the boundary layer is proposed.

Design and Non-Linear Modeling of New Wind Girder Used for Bolted Tanks

Large-capacity bolted cylindrical tanks for liquid storage are used in many applications. The tanks are made of thin steel sheets that are connected by bolts. A common problem associated with tanks is deforming under extreme loads. Adding wind girders to the tank increases the tank’s buckling capacity, which is defined as the limit load at which the structure loses stability. The girders are usually placed in the horizontal joints of the tank wall. The girders are bent from standard or non-standard steel bars with a uniform cross-section. This type of design is difficult to produce, especially with large profiles or large curvatures, to avoid distortion of the cross-section during bending. Furthermore, the girders are customized to the given openings and curvature for various tank diameters. The resulting solution is then uneconomical and more complicated to store. This paper deals with the design and non-linear modeling of a new shape of wind girder for bolted tanks that eliminates the above-mentioned disadvantages. To analyze the new shape of the girder, a non-linear numerical model of an open-topped tank with various dimensions is designed to study its buckling capacity.

Interaction of open-top, short, cylindrical tank with wind-driven rain

Driving rain or wind-driven rain (WDR) is defined as rain, falling in an inclined manner due to the driving force of the wind, inflicting damage to the envelope of building, due to rain droplet impingement, hygrothermal effect, and, rain water ingress. When rain is driven by wind, especially high wind (during storm, cyclone, etc.), the rain droplet impact can increase. There is no availability of literatures on the interaction of shell structures with driving rain, which incurs damage to the thin wall of the tank through droplet impact. This scope is the main motivation behind the present study, which is focused on fluid–structure interaction analysis of an open-top, ground-supported, cylindrical tank with a slenderness ratio of 1.0, affected by wind driven rain. The thickness of the tank wall is varied, and, open terrain condition is considered. The study exhibits that the force coefficient (Cf) of WDR is higher between 0° to 53° peripheral position and decreasing upto 140° circumferential location. Maximum 28% increase of force coefficient of WDR noticed for 45° position in comparison to the wind force coefficient. Also, the top of the tank wall exhibits greater deformation and vulnerable under the effect of wind-driven rain load. Also, it is evident that 0° to 18°, and, 0° to 27° circumferential area exhibit higher deformation for radius: thickness (R/t) ratios 500, and 250, respectively. In case of R/t ratios 125, and 166.67, the higher deformation zone is distributed 0° to 15° and 77° to 82° peripherally. This deformation behaviour of the tank wall, shows that the open-top tanks need to be stiffened at the top to withstand the wind-driven rain force. The magnitude of deformation exhibits increments with the decrease in the thickness of wall of the tank. Maximum deformation is observed for lowest thickness of the tank wall.

Effect of simplified wind girder modelling on MNA-LBA analysis of open steel tanks

The MNA/LBA design methodology for metal shells, including open-top tank steel shells, plays an important role in the European Standard on Strength and Stability of Shell Structures. However, when using this design format, particular doubts as to the correctness of the obtained results may arise when simplifications are used in modelling of key elements of tank structures in order to improve modelling and numerical calculation processes. This paper presents the results of numerical studies that address the question of how the simplifications in the modelling of the primary wind girder affect the values of the elastic buckling resistance and the plastic reference resistance determined from linear bifurcation analysis (LBA) and materially nonlinear analysis (MNA), respectively. Forty-two computational models of wind-loaded open storage tanks with three height-to-diameter ratios and with variable or constant wall thickness of a cylindrical shell, equipped with six different representations of the wind girder, were investigated in order to provide guidelines in the above-mentioned scope. It has been proven that the applied simplifications in the modelling of the primary wind girder allows for relatively faithful representation of the reference models, i.e. models in which the stiffening ring was modelled using shell finite elements, in the LBA analysis. In turn, a varied influence of the applied simplifications in modelling on the results of the MNA analysis was observed. The obtained results indicated a limited range of applicability of the results of the materially nonlinear analysis for the formal assessment of the relative overall slenderness of the considered shells. Finally the obtained results allowed for the formulation of practical conclusions for the purposes of design of open-top steel tanks using the MNA/LBA methodology.

Fragility of open-topped oil storage tanks under wind in Patagonia

Fragility of open-topped oil storage tanks under wind in Patagonia

Wind Buckling Analysis of a Large-Scale Open-Topped Steel Tank with Harmonic Settlement-Induced Imperfection

In this study, the wind buckling capacity of an open-topped steel tank with harmonic settlement-induced imperfection is numerically investigated. Although the single effect of the wind load or differential settlement on the open-topped steel tanks is widely studied, the interaction of the two loads to the tank shell is scarcely examined. The prototype of a 100,000 m3 open-topped steel tank with a floating roof is selected, and the harmonic settlements (wave numbers n = 2, 3, and 4) and the wind profile considering internal pressure (EN 1993-4-1) are applied. Firstly, the finite element model is established and validated by the replication of peer-reviewed research. Then, the wind buckling analysis of the tank shell with harmonic settlement-induced imperfection is studied. Next, the effects of the harmonic settlement-induced imperfection (HSII) and the wind attack angle (WAA) on the wind buckling capacity are discussed. The results show that the effect of the HSII on the wind buckling capacity is complex. When the wind attack angle is the case of β=0°, the wind load capacities (λcig) with HSIIs decrease to 73.4% (wave number n=2), 37.5% (wave number n=3) and 41.3% (wave number n=4) of the non-settlement wind load capacity (λcg). Given that the case of β=0° is the basis, when the harmonic settlement level is low, such as settlement load No.1 and No.2, the biggest increase of wind buckling capacity is less than 20% with an exception; when the harmonic settlement level is high, such as settlement load No.3, No.4 and No.5, the biggest increase of wind buckling capacity is more than 40%, with a few exceptions.

Buckling resistance of the cylindrical shells with two secondary stiffening rings under external pressure

The common way to amplify strength and stiffness of the tank wall is to use the stiffening rings. These stiffening rings can be classified as the primary and secondary stiffening rings (PSRs and SSRs). PSR is placed around the top of the tank shell and it assists to avoid ovalization at the top when the open-top tank is exposed to the external pressure. PSR having small dimensions may be used for fixed roof tanks since the roof system attached to the top of the cylindrical shell provides a natural restraint at this location. On the other hand, one or more SSRs may be required to preclude local buckling in both fixed and open-top cylindrical steel tanks (CSTs) which are exposed to external pressure. The requirements of single secondary stiffening ring have been investigated in detail in previous studies. However, in same cases, a single SSR does not provide sufficient resistance to maintain stability over the entire shell height. Thus, buckling capacity of the CSTs with two identical secondary stiffening rings have been explored in this present work. Pursuant to this aim, the requirements for stiffness of the SSRs which are given in terms of minimum second moment of area (SMA) were evaluated by performing Linear Elastic Bifurcation Analysis (LBA) of CSTs under uniform external pressure. Analysis results show that minimum SMA expression proposed by Blackler underestimates critical buckling value for the tanks, having especially low height-to-diameter ratios and low radius-to-thickness ratios. Furthermore, to trace strength reduction in the tank due to geometrical imperfections, Geometrically Nonlinear Analysis including Imperfections (GNIA) was performed. Analysis findings affirm that thin-walled structures are very sensitive to geometrical imperfections.

Stiffness requirements for wind girders in open-top cylindrical steel tanks

Aboveground cylindrical storage tanks are very thin shell structures which are prone to buckling when subjected to wind pressure. Both external and internal pressures are developed due to wind action, and the magnitudes of the pressures generally vary around the circumference. A wind girder is generally used in open-top cylindrical tanks to increase their resistance against buckling. The wind girder must have adequate strength and stiffness in order to fulfill its function properly. Widely used design specifications provide recommendations for the design of the wind girder. Strength requirements are given in terms of stress resultants, while a minimum second moment of area is provided as a stiffness requirement. The recommendations for the stiffness requirement were developed by conducting Linear Elastic Bifurcation Analysis (LBA) of cylindrical shells subjected to uniform external pressure. This paper explores stiffness requirements for the wind girder in open-top cylindrical steel tanks. The relationship between the buckling strength and the second moment of area of the wind girder was explored through a finite element parametric study. Tank shells with different radius-to-thickness and height-to-diameter ratios and having different wind girder sizes were investigated by means of LBA. A buckling strength curve was developed based on the LBA results where the strengths can be predicted with 90% accuracy. In addition, a new second moment of area requirement was proposed. The parametric study was extended to investigate the behavior using Geometrically Nonlinear Analysis including Imperfections (GNIA). The same tank geometries were studied using GNIA and considering different imperfection amplitudes. A buckling strength curve, which takes into account imperfection amplitudes, was developed to be used in design.

The stability of anchored cylindrical steel tanks with a secondary stiffening ring

Cylindrical steel tanks are used in most countries to store bulk volumes of liquid products such as oil, water and chemicals. These structures are commonly constructed from thin steel plates. The thin wall makes the tank vulnerable to buckling under external pressure due to wind, or to a partial vacuum when it is empty or partially emptied. A stiffening ring is widely used to enhance the strength of the tank wall against external pressure instability. Recent research by the author has determined stress resultants in order to provide a rational design procedure for the primary stiffening ring in open-top steel tanks considering interaction between the ring and the cylindrical tank shell. In addition to primary stiffening ring, one or more secondary stiffening rings are generally needed to enhance the buckling resistance under external pressure and wind. From this premise, the strength and stiffness requirements for the secondary stiffening ring in anchored cylindrical steel tanks are explored in this new study. Pursuant to this aim, the stress resultants in the isolated secondary stiffening ring subjected to non-uniform wind loading are derived using Vlasov's curved beam theory. Next, a new shell-to-ring stiffness ratio is presented by considering the ratio of the stiffness of the cylindrical shell to that of the secondary stiffening ring. In addition, a parametric study employing finite element analysis is performed to obtain the required strength and stiffness of the secondary stiffening ring in anchored cylindrical steel tanks. The variations in response quantities are expressed as a function of the proposed shell-to-ring stiffness ratio. These findings are finally expressed in terms of simple equations that can be easily used in practical design.

IMPACT ANALYSIS of CYLINDRICAL STEEL WATER STORAGE TANKS UNDER the SEISMIC ACTION

Cylindrical steel liquid tanks are widely used to store various liquids such as water, oil and industrial chemicals. In recent years, they are used in nuclear power plants for cooling purposes. Petroleum or other hazardous chemicals in steel liquid tanks can cause large financial and environmental damage due to damages in tanks during the earthquake. The main goal of this paper is to reveal buckling shape of cylindrical steel tanks with nonlinear seismic analysis according to roof shapes. Roof shapes were determined as open-top, flat-closed, conical-closed and torispherical-closed tanks. For this aim, El-Centro earthquake recording of 0.22 seconds was used for determine the significant shell buckling events. In addition, this earthquake values are ideal for impact analysis because ANSYS Workbench “Explicit Dynamics” tool provides very good results in the dynamic analysis of structures under destructive and short-term forces. In order to provide the interaction between the water and the tank wall, the "Eulerian Body" mesh technique is preferred in “Explicit Dynamics” model. As a result of this study, many collapse events were determined due to seismic ground motion in cylindrical steel liquid storage tanks. If the tank was closed in the shape of a torispherical, less buckling could occur in the tank.

Design of cylindrical steel liquid tanks with stepped walls using One-foot method

Cylindrical steel tanks are used in most countries to store bulk volumes of both solid and liquid products such as water, oil, gasoline and grain. Such steel tanks are prone to buckling when subjected to external pressure either due to vacuum or due to wind. These types of shell structures are generally controlled by elastic buckling failure because of the thin wall thickness. Cylindrical shells are commonly constructed with stepwise variable wall thickness due to economic reasons. The thickness of the tank shell wall is designed to increase from top to bottom because the stress resultants on the tank wall gradually increase towards the base of the tank. For open-top tanks, a primary stiffening ring is required at or near the top to maintain roundness under all loads. Stress resultants in a primary stiffening ring were previously identified by the Author for uniform wall thick tanks. In this new study, the applicability of this hand calculation method in stepped wall tanks has been investigated. Pursuant to this goal, a specified tank shell was designed considering One-foot method. Then, the stepped wall tank was transformed into an equivalent 1-course tank for hand calculation. Using the previously developed hand calculation method by Author, a test for the in-plane bending moment in the ring was conducted to achieve an acceptable value for stepped wall tanks. The analysis results show that the previously proposed method for uniform wall thick tanks may also be used for stepped wall tanks considering an equivalent thickness. On the other hand, using Linear Buckling Analysis (LBA), the buckling mode was obtained for two different stepped wall tanks in the study.

A FLAT-PARALLEL TYPE PHOTOBIOREACTOR DESIGN FOR SEWAGE WATER TREATMENT

Organic and inorganic substances which were released into the environment as a result of domestic, agricultural and industrial water activities lead to organic and inorganic pollution. Effluent is loaded with inorganic nitrogen and phosphorus and causes eutrophication. Microalgae culture offers an interesting step for wastewater treatments, because they provide a tertiary biotreatment coupled with the production of potentially valuable biomass, which can be used for several purposes. Problem statement. The purpose of this article is to develop a photobioreactor design for wastewater treatment in which the application of new elements and connections reduces material consumption for the manufacture of transparent flexible tanks, reducing labor costs for installation and dismantling of tanks, and preventing the mixing of immobilized algae and their removal from the working area of the photobioreactor. Research methodology. Methods were based on a systematic analysis of theoretical research, synthesis, anology and comparison of various photobioreactor designs. Results and discussion. The problem is solved by the fact that the photobioreactor is made in the form of a transparent flowing rectangular open-topped tank. The flowing flat transparent containers, made with flexible material, are vertically, parallel to each other attached to the bottom of the tank with quick-release fasteners inside. Pipelines for supply saturated by carbon dioxide wastewater and microalgae are connected through non-return valves. Pipelines for drainage of a mixture of microalgae with residual wastewater are connected through non-return valves. Pipelines for drainage of treated wastewater and valves for release of accumulated gases are connected in the upper airtight part. The pipeline for the treatment of treated wastewater is connected to the guide tray for supplying treated wastewater in the middle of a flowing rectangular open-topped tank. A carbon dioxide supply pipeline is connected to the inlet part of the wastewater supply pipeline. At the outlet of the pipeline for the removal of a mixture of microalgae with residual wastewater is a separator of microalgae to separate the return and excess biomass to supply separated from microalgae wastewater in a flowing rectangular tank. Conclusions. The proposed construction of photobioreactor can have good perspectives to be use in communal services for sewage water purification from biogenic elements. Improved photobioreactor design also can be used in sewage systems of enterprises of different branches of industry, when it is necessary to purify sewage water. The proposed flat-parallel type photobioreactor design for sewage water treatment differs by changing the geometric shape of the tanks, which serves a mixture of water and microalgae, resulting in a reduction in material costs for the manufacture of tanks and labor costs for their maintenance

A study on the buckling behavior of in-service large open-topped oil-storage tanks

Oil storage tank is a typical thin-walled structure which is prone to buckling under external load. In this paper, the buckling behavior of the in-service open-topped oil-storage tank under wind loads is studied by analyzing four large in-service oil-storage tanks of 50000–150000 cubic meters. First, the general buckling behavior of oil-storage tanks under the external pressure without reinforcement device is analyzed by linear buckling. And the calculation accuracy of three calculation formulas for the critical buckling load of the storage tanks under uniform pressure is compared. Then the nonlinear buckling analysis is carried out by using the arc-length method, and the results show that the imperfection of the classical buckling mode has a significant influence on the buckling behavior of the storage tanks without reinforcement device. Finally, this paper focuses on the influence of wind girder and other reinforcement device on the buckling behavior of the tank, as well as the strengthening mechanism of the stored liquid on the in-service oil-storage tank. The results show that the reinforcement device affects the buckling behavior of the oil-storage tank by strengthening the stiffness of the tank top, while the stored liquid increases the stiffness of the tank bottom. Compared with the oil-storage tank without reinforcement device, the reinforcement effect of liquid on an oil tank equipped with a reinforcement device is more significant.

Experiments on Stability Performance of Thin-Walled, Open-Top Steel Storage Tanks Subjected to Local Support Settlement

Local support settlement is a typical differential settlement which may take place under steel storage tanks and can adversely affect the stability performance of such thin-walled structures. Considering the practical applications of the thin-walled steel storage tanks in industry, proper treatment of this problem is essential to ensure the high structural performance of such members which albeit requires detailed investigations. On this basis, this study investigates the effects of the local support settlement on the buckling stability of two tanks without and with a top stiffening ring through the experimental and numerical approaches. The considered tanks are small-scale models with the height-to-radius and radius-to-thickness (slenderness) ratios of 1.0 and 834, respectively. Both experimental and numerical results show that the behavior of the tank under the local support settlement is nonlinear. Moreover, the effectiveness of the top stiffening ring in limiting the buckling deformation and improving the buckling performance of the tank is demonstrated in this study.

Fitness-for-service of open-top storage tanks subjected to differential settlement

A method for evaluating the mechanical integrity of open-top cylindrical storage tanks subjected to a differential settlement is given. The settlement profile underneath the bottom circumference of the tank shell can be transformed into different harmonic components using the Fourier transformation. The existing method in American Petroleum Institute’s standard API 653, which is currently used by the industry in North America, does not differentiate the effect of different harmonic components. Nevertheless, the proposed method evaluates a cumulative damage factor by considering the effects of first five harmonic components individually. The paper further discusses other limitations of the existing method in API 653 document. Numerous finite element analysis (FEA) simulations are conducted to formulate and validate the proposed method by employing geometric nonlinear algorithm with nonlinear plastic material properties (GMNA) in ABAQUS finite element software. The trend for limiting settlement values with respect to different harmonic components under consideration and different tank geometries are discussed. The proposed method is validated by performing FEA using four actual settlement data profiles on different tank geometries. Lastly, the comparison is drawn between the FEA results, the existing API 653 method and the proposed method. The results of the allowable settlement indicate that the existing method is not consistent with the FEA findings. For some of the actual settlement data, the existing method results in overly conservative values and for others it gives non-conservative values. Thus, the existing method may not capture the true behavior of tanks under settlement and needs modifications. The results of allowable settlement from the proposed method are found to be consistent with the FEA results for all different settlement data and tank geometries. Therefore, it is recommended that the new method is used instead of the existing method.

The Ethical Assessment of Touch Pools in Aquariums by Means of the Ethical Matrix

Touch pools are popular open-topped fish tanks often found in aquariums where visitors may interact with animals, by touching and sometimes even feeding them, for educational and recreational purposes. However, although animal interactions are becoming increasingly popular in recent years, the welfare impact on the animals and the educational effectiveness of such interactions is under debate. Awareness concerning the different, and sometimes controversial, aspects connected with such interactions has spread. The aim of this paper is to investigate the ethical issues arising from the presence of touch pools in aquariums and facilities alike. In particular, possible sources of moral conflicts between five interested parties will be identified and discussed: biodiversity; aquariums; staff involved with touch pools; individual animals used in the touch pools; visitors interacting with animals in touch pools. In order to assess the framework of ethical demands from different parties, it will be used an analytical tool provided by a revised version of the Ethical Matrix.

Buckling analysis of open-topped steel tanks under external pressure

Oil storage tanks are typically thin-walled structures which are susceptible to buckling under external load. This paper explores the buckling behavior of two in-services 100,000 m3 open-topped tanks under external load by finite element simulation. The finite element analyses are first carried out to explore the stability of in-services tanks under the uniform external pressure and the wind load. And comparison with that three formulae which uses for calculating the critical buckling load of the tank under uniform external pressure. Then carried out the nonlinear buckling analysis by arc-length method, the results show that for in-services tanks, the linear elastic bifurcation analysis also is a good signal for the buckling load. Finally, this paper focus on the influence of wind girders and other reinforcement devices on the buckling behavior of in-services tanks and the strengthening mechanism of the stored liquid to in-service tanks with reinforcement devices. The reinforcement device affects the buckling behavior of the oil-storage tank by strengthening the stiffness of the top of the tank. However, the stored liquid through increasing the stiffness of the bottom of tanks to add the stability of tanks. And the result shows that compared to the oil-storage tank without reinforcement devices. The strengthening effect of the liquid on the tank containing reinforcement devices is more significant.

Dynamic analysis of aboveground open-top steel tanks subjected to wind loading

Aboveground steel tanks are prone to buckle under wind loading if they are empty. Geometrically nonlinear explicit dynamic analysis of empty open-top tanks subjected to wind loading are conducted using finite element analysis (FEA). Tanks with five different height to diameter aspect ratios, 4.0, 2.0, 1.0, 0.4, and 0.2, are adopted. Tanks are subjected to a gust of wind which fluctuates in magnitude over time to investigate whether a minor fluctuation, 10% of the average pressure, will trigger resonant behavior. Tanks with geometrical imperfections are also investigated using both dynamic analysis and static geometrically nonlinear analysis including imperfection (GNIA). It is found that, no matter if the tank does or does not have geometrical imperfections, resonance is not observed. Thus, a static analysis may be adequate for a practical tank design. The natural vibration frequencies of empty open-top tanks are studied as well, and comparisons with theoretical solutions and FEA results from the literature are presented. The effective modal mass is discussed to investigate the dynamic characteristics of the tanks examined. Insights for conducting an explicit dynamic analysis, including converged mesh size and time step limits, are also presented.