Fem Seismic Analysis of Steel Tanks for Oil Storage in Industrial Facilities (original) (raw)
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SEISMIC ANALYSIS OF STEEL STORAGE TANKS: OVERVIEW OF DESIGN CODES USED IN PRACTICE
Seismic provision of all types of structures is of paramount importance in regions defined by medium and high seismic hazard. This is all the more true in the case of steel storage tanks, as these often contain toxic, flammable and explosive substances or the fuels needed for post-state recovery after a catastrophic event. Additionally, steel storage tanks could be an integral part of special facilities related to national security and defence. The current paper presents an overview of the European design codes used in practice regarding the analysis, behaviour and design of steel tanks under earthquake loading, namely EN 1998-4 (BDS EN 1998-4:2006, along with the national annex BDS EN 1998-4:2006/NA:2012) and EN 14015 (BDS EN 14015:2005). Other legislative documents-API Standard 650 and API Standard 620 are also considered. The aim of the paper is to compare the provisions provided by the aforementioned documents focusing on the aspects that require further investigation and regulation, as well as those not dealt with in the regulatory framework. Special attention is paid to the effects that a seismic event would have on the stationary roofs of vertical cylindrical steel storage tanks.
Analysis and structural behavior of cylindrical steel tanks under seismic effects
International Conference of Metal Structures 2011 (Poland), 2011
"The use of large steel oil storage tanks that provide adequate safety and reasonable economy has always been an issue of major concern for the petroleum industry. To this end, efficient design and comprehensive analysis of such structures is important. This paper addresses specific issues regarding the analysis and behavior of cylindrical self supported tanks under earthquake loading and more importantly their seismic design, by comparing current codes used in practice with the finite element method (FEM). The results refer to two large cylindrical tanks and they show that even though the current design methods fail to describe their exact behavior, they do not violate fundamental safety considerations."
Journal of Loss Prevention in the Process Industries, 2013
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 FRAGILITY ANALYSIS OF STEEL STORAGE TANKS
Earthquakes can cause significant damages to industrial liquid storage tanks resulting in losses of functionality, fires or environmental contamination due to the leakage of hazardous chemicals. Typical damages of ground supported tanks during past earthquakes were in the form of cracking at the corner of the bottom plate and compression buckling of tank wall due to uplift, sliding of the base, anchorage failure, sloshing damage around the roof, failure of piping systems and plastic deformation of base plate. Liquid tanks can be also located at some elevated positions due to operational purposes. This makes them susceptible to collapse due to increased base shears and overturning moments. The seismic response of elevated tanks has been widely investigated in the past considering different materials and configurations of support structures. This paper addresses the problem of elevated tanks with particular attention focused on the steel storage tanks resting on short RC columns. The vulnerability of a real example of elevated tanks is assessed though the probabilistic analysis performed using non-linear lumped mass models. Consequently different fragility curves are built for identifying the most important damage states and calculating the corresponding probability of occurrence. The results show how the support structure, especially when composed by RC columns, is the most influencing one, whereas the remaining damage states have a limited influence.
ISRN Civil Engineering, 2012
The seismic behavior of steel tanks is relevant in industrial risk assessment because collapse of these structures may trigger other catastrophic phenomena due to loss of containment. Therefore, seismic assessment should be focused on for leakage-based limit states. From a seismic structural perspective, damages suffered by tanks are generally related to large axial compressive stresses, which can induce shell buckling near the base and large displacements of unanchored structures resulting in the detachment of piping. This paper approaches the analysis of seismic response of sliding, nonuplifting, unanchored tanks subject to seismic actions. Simplified methods for dynamic analysis and seismic demand estimation in terms of base displacement and compressive shell stress are analyzed. In particular, attention is focussed on some computational issues related to the solution of the dynamic problem and on the extension of the incremental dynamic analysis (IDA) technique to storage tanks.
Effect of the model updating on the earthquake behavior of steel storage tanks
Journal of Constructional Steel Research, 2010
In this paper, effect of the finite element model updating on the earthquake behavior of steel storage tanks considering fluid–structure interaction is investigated. For this purpose, a cylindrical steel storage tank filled some liquid fuel oil located in Trabzon, Turkey is selected as an example. Initial finite element model of the storage tank is developed by ANSYS software and dynamic characteristics (natural frequencies, and mode shapes) are determined analytically. Ambient vibration tests are conducted on the storage tank under natural excitations to obtain dynamic characteristics (natural frequencies, mode shapes and damping ratios), experimentally. Peak Picking technique in the frequency domain is used to extract experimental dynamic characteristics. When the analytically and experimentally identified dynamic characteristics are compared to each other, some differences are found between both results. To minimize these differences, initial finite element model of the storage tank is updated according to experimental results using some uncertainties modeling parameters such as elasticity modulus. To investigate the effect of finite element model updating on the earthquake behavior of the storage tank, earthquake analyses are performed before and after model updating. In the earthquake analyses, YPT330 component of 1999 Kocaeli earthquake is selected and applied to the models in the horizontal directions. It is seen from the analyses that the displacements and the stresses after model updating are more effective than the displacements and the stresses before model updating.
Seismic Demand Analysis of Steel Storage Tanks
wpage.unina.it
Seismic behaviour of steel tanks for oil storage is relevant in the light of industrial risk assessment because collapse of these structures may trigger other catastrophic phenomena, as fires or explosions due to loss containment. Therefore, seismic assessment should be focussed on leakage-based limit states. Damages suffered by storage tanks under seismic actions are generally related to large axial compressive stresses that can induce shell buckling near the base and to large displacements of unanchored structures leading to detachment of piping, liquid. The present paper approaches the analysis of seismic response of sliding, non-uplifting, unanchored liquid storage tanks subject to three-dimensional ground motion. The algorithm to solve the equation of motion for a simplified tank's model is proposed and a sample estimation of the seismic demand by incremental dynamic analysis is discussed.
Seismic Performance of Storage Steel Tanks during the May 2012 Emilia, Italy, Earthquakes
Journal of Performance of Constructed Facilities, 2014
Field observations following the May 2012 Emilia, Italy, earthquakes have revealed the seismic vulnerability of storage steel tanks typical of the past Italian design practice, highlighting structural deficiencies observed during previous events in other areas and mostly related to lack of structural seismic design and detailing, lack of redundancy, and inadequate anchorage design and execution. Damage was disproportionately high, considering the moderate size of the events (M W ¼ 6.11 and M W ¼ 5.96 on 20th and 29th May, respectively). Failure modes observed are reported and classified. Comparison is provided with the results of high-definition finite element (FE) dynamic simulations, performed on tanks representative of those inspected. Numerical analyses, accounting for material and geometrical nonlinearities, at the element level, as well as for fluid-structure interaction through highly nonlinear methods, were able to capture the stress/strain concentrations that caused them to collapse. Elephant's foot and diamond buckling induced by hydrodynamic pressures as a result of inertial forces imparted during the earthquakes were reproduced, as well as shear-buckling failure of leg-supported tanks or sliding of unanchored systems.
Seismic vulnerability analysis of storage tanks for oil and gas industry
Pipeline Science and Technology, 2018
IL AND GAS TRANSPORTATION LINE components are particularly vulnerable to natural hazard events. Steel tanks are recognized as the most vulnerable equipment to seismic action, whose damage may result in the release of materials and thus the increase of overall damage to nearby areas. The seismic vulnerability of tanks is commonly expressed by fragility curves, which are conditional probability statements of potential levels of damage over a range of earthquake intensities. This paper aims to present an appropriate procedure for analytically deriving fragility curves of tanks with the treatment of uncertainties. At first, the analysis of critical damage states of steel storage tanks observed during past earthquakes is presented. Possible numerical models of tanks subjected to earthquakes are then discussed. An overview of seismic fragility methodologies for tanks is next presented. Attention is paid to an analytical method, i.e. cloud method, which is conducted by using a probabilistic seismic demand model and non-linear time-history analyses. A broad tank, which is located in a refinery in Italy, is considered for the fragility evaluation. Resulting fragility curves for critical damage states of the tank, such as the plastic rotation of the shell-to-bottom plate joint, the buckling of the bottom shell course, and the material yielding of the shell plate, show a high seismic vulnerability of the tank.
Structural issues in seismic risk assessment of existing oil storage tanks
2002
Abstract Large regions in many countries are exposed to earthquakes, thus seismic risk evaluation is a relevant issue and requires specific knowledge development and integration between different skills. Failure of critical constructions can have direct and indirect influence on public safety; in fact, pollution or damages due to explosions can be related to collapse of industrial facilities.