Unanchored steel storage tanks, commonly used in industrial facilities, can suffer damage during major earthquakes due to various failures. To better understand the seismic behaviour of such ...structures, a pushover-based seismic performance assessment of four tanks with varying slenderness ratios was performed. The emphasis was placed on understanding the relationship between engineering demand parameters, tank slenderness ratio, and wall geometrical imperfections, which were, however, imposed only to the lower course around the tank circumference to assess the upper limit of the effect of geometrical imperfections on the elephant-foot buckling (EFB). The findings reveal that axial compressive stress in the tank wall correlates with increased slenderness and geometrical imperfections. This implies that the axial compressive stress in the wall of broader tanks is relatively low, and the bulging at the bottom of the wall is mainly due to high hydrodynamic pressure and the resulting hoop stress. In contrast, the wall of slender tanks buckles primarily due to high axial stresses, leading to EFB. Through dynamic analysis, the study showed that the pushover analysis can underestimate the axial stress if the tank’s base plate is uplifted significantly before EFB occurs. The effect of the impact should thus be considered, especially in the case of slender tanks, because the base plate uplift mechanism is more pronounced than in broader tanks. Further research is needed for a more accurate prediction of the axial compressive stress in slender tanks. However, the safety margin in the post-yielding range is low because the yielding area of the tank wall rapidly increases after the occurrence of steel yielding. In the absence of a detailed 3D model of tanks, simplified formulas for estimating stresses in the tank wall may be used for the broader tanks but not for more slender tanks because of their inability to simulate the highly non-linear relationship between the ground motion intensity and the stresses observed in the plastic region of the tank wall.
•Slenderness and geometrical imperfection correlated to axial stress in tank walls..•Slender tanks buckle from axial stress, broader ones also due to high hoop stress.•Dynamic analysis revealed base plate impact triggers EFB, mainly in slender tanks..•Dynamic analysis including base plate-foundation impact necessitates further research..•Simplified formulas to evaluate slender tank stresses overestimate seismic capacity.
In this study, the seismic response and buckling of aboveground cylindrical steel liquid storage tanks subjected to horizontal components of earthquake ground motions is investigated using ...incremental dynamic analyses (IDA). A broad steel tank with diameter of 30 m and height to diameter (H/D) ratio of 0.40 was designed using API 650 standard. The incremental dynamic analyses of liquid storage tank were performed for seven real seismic ground motions, which were scaled for PGAs of 0.05g to 0.50g. To verify the accuracy of the propose finite element model of the tank-liquid system, natural periods of the tank-liquid system vibration modes computed from finite element analysis compared to those obtained by analytical solutions and other numerical study. Small difference between natural periods indicates the acceptance accuracy of the finite element model. The mean peak base shear and overturning moment of the steel tank are estimated using mass spring model and compared with those obtained by finite element model. The mean peak base shear and overturning moment from finite element model greater than those obtained by mass spring model for PGA less equal 0.20g and vice versa for PGA from 0.30g to 0.50g. The incremental dynamic analysis results show that buckling of tank shell occurred at a height of 2.8 m above the tank base. Also mean critical horizontal peak ground acceleration (critical PGA) and mean critical dynamic base shear force, which induces buckling at the bottom of the cylindrical shell, are estimated.
Abstract Unanchored steel storage tanks are used in industrial plants to store oil and other petrochemical liquids. In a major earthquake, such tanks may sustain different types of damage, including ...elasto‐plastic buckling in the shape of an elephant's foot, which is the object of the research. The methodology introduced in this paper consists of cloud‐based 1D site response analysis (SRA) and pushover‐based seismic performance assessment of the tank wall using a 3D non‐linear model of the tank. The SRA, which considers the recorded ground motions on the rock outcrop and the sample of interval shear‐wave velocity profiles, is carried out to estimate spectral accelerations at the tank impulsive period. By adopting the code‐based model of hydrodynamic pressures, the seismic demand on the tank wall is then calculated by pushover analysis. The risk‐targeted decision model is used for safety verification. The proposed methodology is demonstrated through an example of a large liquid storage tank for which it is shown that the fragility function for peak ground acceleration at the rock outcrop is on the left side of the target fragility function, indicating that the tank cannot be considered safe from elephant‐foot buckling. The introduced assessment process is relatively simple if the cloud‐based SRA is automated. However, further experimental and numerical investigations are required to confirm the validity range of the pushover analysis for the seismic performance assessment of tanks.
AbstractLarge and small cylindrical shells have long been used as tanks and silos to store materials such as oil and its derivatives. The radius-to-thickness ratio of these shells is 500∶2000; as a ...result, buckling collapse of these thin-walled structures is of major concern for designers. The present study examined inelastic buckling behavior of cylindrical shells near the base, known as elephant foot buckling. This form of buckling occurs under high internal pressure exerted simultaneously with axial compression. The buckling of cylindrical shells subjected to combined axial loads and internal pressure was experimentally studied and tested and a new method of strengthening steel cylindrical shells using fiber-reinforced polymer (FRP) composite materials is presented. The proposed method was studied by numerical methods using a nonlinear algorithm, and the results were evaluated for resistance to buckling of cylindrical shells. The results provide effective and useful information for use in retrofitting cylindrical shell tanks.
This paper presents an experimental and analytical investigation on the performance of partial penetration welds used to adjoin steel plates in irregular shaped multicell concrete filled steel tubes. ...The experimental program of this study is designed based on an actual implementation of such members as mega columns in a super high rise building in China. A total of six specimens are designed with different plate arrangements for the purpose of testing the performance of the partial penetration welds at different locations of the specimen. The designed specimens are tested under different load procedures and directions; this is achieved by placing them in vertical and slantwise manners between two loading plates which impose monotonic and cyclic actions. The failure conditions of each of the tested specimens are presented and discussed in detail and are based on the conclusions drawn from the experimental observations; the partial penetration weld at the corner of the tested specimens is found to be the most vulnerable. To facilitate large scale analysis, a finite element model constructed by the finite element analysis program ABAQUS is verified against experimental results. The evaluation of the stress at the partial penetration welded corner is carried out following an empirical procedure, which is adopted due to the complexity of the problem domain. The adopted procedure consists of two steps: the first one is to initially evaluate the stress based on an existing method in the literature, and the second one is to fit the results of the initial evaluation with the finite element model results based on parametric and regression analysis. After performing regression analysis, a formula to predict the weld stress is concluded, and the results of the proposed equation are found to be satisfactory when compared with the finite element model results.
Assuming axisymmetric buckling and according to the adjacent equilibrium criterion, a buckling critical stress formula of a perfect tank wall is first obtained through analysis of elastic–plastic ...buckling carried out by J2 plastic flow theory. Furthermore, combining the current tank seismic design standards and the results obtained in this paper, a new critical buckling stress formula of the tank wall is derived after correction for material plasticity by introducing a plasticity influence coefficient. Comparisons between the results obtained and those from the relevant formulas in the design standards of America, Japan, China and Europe are also performed. Our research shows that under interaction of high hydraulic and axial compression, the material properties of the tank wall change rapidly, and the buckling strength of the tank wall also decreases rapidly. The relation between the tank wall buckling critical stress and the hydraulic pressure is similar to Rotter's semi-empirical formula. The results presented in this paper can provide technical support in further protection of large oil storage tanks.
These are buckling critical stresses of 5 × 104 m3 oil tank calculated by four standards and formulas obtained in this paper. With the increase of circumferential stress of the tank wall, buckling critical stresses from America, Japan and China standards keep constant, while values calculated by Europe standard and formulas in this paper decrease. This phenomenon is attributed to material plasticity. Display omitted
► We propose a simplified analytic model for large oil storage tank suffered elastic–plastic buckling. ► Elastic-plastic buckling analysis of a large oil storage tank was carried out by incremental theory of plasticity. ► A critical stress calculation formula of tank wall instability considering the correction of material plasticity was derived. ► Buckling strength of the tank wall would decrease rapidly under the interaction of high hydraulic pressure and axial pressure.
API650-2008 is one of the prominent codes consisting of seismic specifications to design steel storage tanks for earthquakes resistance. In spite of the code's broad application, there are some ...failure modes such as slide bottom, elephant-foot buckling, sloshing and uplift needing more evaluation. In this paper, 161 existing tanks in an oil refinery complex have been classified into 24 groups and investigated using both API650-2008 rules and numerical FEM models. Failure modes and dynamic characteristics of studied models have been calculated by numerical FEM analysis and compared with code requirements. The results demonstrate that, in some cases, there are some imperfections in the code requirements that require further investigation.
► Seismic performance of liquid storage tanks in an oil refinery complex investigated. ► Failure modes of studied steel storage tanks calculated by FEM analysis. ► Numerical FEM analysis results compared with API650-2008 code requirements. ► We report some imperfections of API650-2008 for seismic design requirements of tanks.
Elephant-foot buckling, characterised by an axisymmetric shell bulging adjacent to the base support, constitutes one of the main modes of failure in seismically-excited steel tanks and in most cases ...results in loss of tank contents due to weld or piping connection damage or may lead to total collapse of the tank. Current design codes deal with this mode of failure as a buckling failure and hence calculate an allowable buckling stress and compare it to the axial stress in the shell. Recent earthquake incidents have shown a compelling need to revise these codes. In this paper, an analytical study is performed using non-linear finite element modelling to investigate this mode of failure. A quasi-static hydrodynamic load is applied to the tank walls simulating the effect of the accelerated contained liquid. The elephant-foot buckling phenomenon was shown to correlate closely with the yielding of the steel shell as indicated by the Von Mises stress. A new design methodology is introduced using the Von Mises stress and an example is presented to illustrate this approach. A detailed analysis is also presented to estimate the location of the elephant-foot bulging failure for existing tanks which could serve as an aid in the process of repairing these tanks.
Elephant-foot buckling, characterised by an axisymmetric shell bulging adjacent to the base support, constitutes one of the main modes of failure in seismically-excited steel tanks and in most cases ...results in loss of tank contents due to weld or piping connection damage or may lead to total collapse of the tank. Current design codes deal with this mode of failure as a buckling failure and hence calculate an allowable buckling stress and compare it to the axial stress in the shell. Recent earthquake incidents have shown a compelling need to revise these codes. In this paper, an analytical study is performed using non-linear finite element modelling to investigate this mode of failure. A quasi-static hydrodynamic load is applied to the tank walls simulating the effect of the accelerated contained liquid. The elephant-foot buckling phenomenon was shown to correlate closely with the yielding of the steel shell as indicated by the Von Mises stress. A new design methodology is introduced using the Von Mises stress and an example is presented to illustrate this approach. A detailed analysis is also presented to estimate the location of the elephant-foot bulging failure for existing tanks which could serve as an aid in the process of repairing these tanks.
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