Seismic Performance of Storage Steel Tanks during the May 2012 Emilia, Italy, Earthquakes (original) (raw)

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.

DYNAMIC BUCKLING OF CYLINDRICAL STORAGE TANKS DURING EARTHQUAKE EXCITATIONS

The behavior of storage tanks' analysis in seismic areas is of major importance because of the strategic nature of these works. The steel cylindrical tanks are the most susceptible to damage due to dynamic buckling during earthquakes. In this study, three criteria are used to estimate the critical peak ground acceleration caused the tank instability. The liquid inside the tank was modeled using specific Ansys's finite elements and fluid-structure interaction. The calculation includes modal and time history analysis, including material and geometric non-linearity. The result values are compared with standard code previsions as well as the results of previous numerical research, and show the need to improve code provisions.

DI Serbatoi Non Ancorati Simplified Models of Unanchored Steel Tanks for Seismic Fragility Analysis

2005

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. 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. The present paper approaches the analysis of seismic response of sliding, nonuplifting, unanchored liquid storage tanks subject to three-dimensional ground motion. A procedure 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. SOMMARIO La risposta sismica dei serbatoi in acciaio per lo stoccaggio di olio combustibile ha grande importanza nelle valutazioni di rischio industriale per le conseguenze che il ...

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.

Seismic Fragility Assessment of Steel Liquid Storage Tanks

Volume 8: Seismic Engineering, 2015

A seismic fragility assessment procedure is developed for atmospheric steel liquid storage tanks. Appropriate system and component-level damage states are defined by identifying the failure modes that may occur during a strong ground motion. Special attention is paid to the elephant’s foot buckling failure mode, where the estimation of the associated capacity and demand requires thorough consideration within a probabilistic framework. A novel damage state is introduced to existing procedures with respect to the uncontrollable loss of containment scenario. Fragility curves are estimated by introducing both aleatory and epistemic sources of uncertainty, thus providing a comprehensive methodology for the seismic risk assessment of liquid storage tanks. The importance of dynamic buckling is acknowledged and the issue of non-sequential damage states is finally revealed.

Buckling Of Liquid-Filled Steel Storage Tanks Under Earthquake Loading

2017

The static and dynamic buckling loads of cylindrical liquid storage tanks were studied in this thesis. Finite element analysis was performed using ANSYS computer program. Twelve different geometries of the cylindrical tanks were analyzed with height to diameter (H/D) ratios of 0.5, 1.0, 1.5, and 2.0 and the diameter to thickness (D/t) ratios of 1000, 1500, and 2000 to cover tall and short cylindrical tanks. The transient dynamic analysis was performed to find the dynamic buckling loads. Applied dynamic loads in this study are horizontal earthquake excitations in terms of acceleration (g) due to gravity. Budiansky and Roth procedure was used to find the dynamic buckling load for both empty and tanks filled with water up to 90% of their height. Analysis results show that the dynamic buckling loads in terms of peak ground accelerations (PGA) are very high which are unrealistic for any recorded earthquake. For the cylindrical tanks filled with water up to 90% of their height; on the oth...

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.