1,344 research outputs found
On the cyclic behaviour of new pier-to-deck connections for short-medium span composite I-girder bridges
No full textShort-medium span steel–concrete composite I-girder bridges are becoming more and more popular, because of the reduced construction time and costs. The light weight renders them particularly suitable also is seismic areas, even though this advantage has not been yet adequately investigated. In fact, in case of seismic loading, significant tensile forces might be exhibited at the bottom flange of the steel girder, especially when monolithic connection between deck and pier is adopted, and the connection, conceived for sustaining prevailing hogging bending moments, could experience an excessive damage. With this aim, the cyclic behaviour of new pier-to-deck joints involving the use of concrete cross-beams (CCB) has been recently analysed within the European project (SEQBRI). This paper deals with the results of a wide experimental investigation of these new joints, performed with the aim of characterizing their hysteretic behaviour. Three different typologies were tested: one designed according to the German standard DIN-FB-104, generally utilized for gravity loads only, and other two types proposed for bridges located in low (VAR-1) and medium (VAR-2) seismicity. A series of displacement-imposed cyclic tests highlighted a good seismic behaviour of all the tested solutions. In particular, the DIN-FB-104 VAR C and VAR-2 displayed a similar global behaviour in terms of maximum force and displacement, but with a more pronounced crack development and buckling of steel girders of the first solution. The VAR-2 also avoids possible pull-out phenomena in the CCB thanks to the beneficial action of pre-stressing bars. A damage analysis of the proposed connections was finally performed in view of the application of the performance-based earthquake engineering methodology and the quantification the seismic performance of this bridge typology, which was among the aims of SEQBRI project
Seismic vulnerability analysis of storage tanks for oil and gas industry
No full textPetrochemical and oil processing plants are complex systems of numerous integrated components and processes, which can make them particularly vulnerable to natural hazard events, in particular, earthquakes. Steel fuel storage tanks are recognized as the most vulnerable equipment to the earthquakes, 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. 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. The attention is paid to an analytical method, i.e., cloud method, which is conducted by using a probabilistic seismic demand model and nonlinear time history analyses. A broad tank, which is located in a refinery of 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
Scores: an algorithm for records selection to employ in seismic risk and resilience analysis
No full textModern approaches for the assessment of seismic behavior of structures (i.e. PBEE) are often based on nonlinear dynamic analyses. In this respect, the selection of ground motion records is of paramount importance, because of the record-to-record variability of the structural response. In the past, selection of natural records was often performed based on the compatibility between the response spectra and a target spectrum, usually derived from a PSHA or a code spectrum. Spectral matching can be considered the most commonly proposed earthquake record selection, currently adopted by many seismic codes. The main problem of this approach is that the record-to-record variability can result excessive, obtaining a considerable scatter in the non-linear response. For these reasons, it is usually preferable to synthetize the seismic hazard properties by using a scalar or vector-valued Intensity Measure (IM). Nevertheless, the selection of efficient, sufficient and practical IMs leads to different approaches, without converging toward a unified approach. Consequently, aim of this paper is to propose a novel algorithm for records selection to employ in risk analysis, which is able to control the dispersion without resorting to the artificial scaling of the accelerograms and thus easily employed in three-dimensional structural analysis. It is based on the idea to control the record-to-record variability rather than to reduce it by scaling the accelerograms. The proposes methodology has been implemented in the software SCoReS and used for the risk assessment of a RC frame structures
On the use of proper fragility models for Quantitative Seismic Risk Assessment of process plants in seismic prone areas
No full textQuantitative Risk Assessment (QRA) is a classical method for the calculation of risk in process plants, which is based on the logic of the consequence analysis. This intrinsically probabilistic method has been thought for classical accident conditions, where the damage events and the relevant consequences start from a preselected component and a standard loss of containment (LOC) and follow all possible scenarios for the calculation of individual and societal risk. This final risk metric is usually expressed in terms of probability of fatality in a specific location of the surrounding area or a certain number of fatalities in the area surrounding the accident. In presence of Na-Tech events, like earthquakes, a multi-source condition can be caused by multi-damage conditions simultaneously involving more than one equipment, which in turn can generate a multiple-chain of events and consequences. In literature, several attempts of modifying the classic QRA approach to account for this important aspect have been formalized without converging toward a unified approach. In this paper, a fragility-based method for Quantitative Seismic Risk Analysis (QSRA) of a process plant is investigated. This method takes into account all possible damage/losses of containment conditions in the most critical equipment, e.g., storage tanks. Fragility curves, which are analytically evaluated for each unit with respect to its seismic damage conditions, are utilized inside the procedure. The Monte Carlo Simulation (MCS) method is then used with the aim to follow all steps of QSRA. In particular, starting from the seismic hazard curve of the site where the plant is placed, a multi-level approach is proposed. In this approach, the first level is represented by the components seismically damaged, whereas the following levels are treated through a classical consequence analysis, including the propagation of multiple simultaneous and interacting chains of accidents. These latter are applied by defining proper correspondences for all relevant equipment between structural damage (i.e., limit states) and LOC events. The application of the method to an actual process plant permits to investigate its high potentiality and the dependency of the risk assessment from the proper fragility models
A probabilistic approach for the assessment of LOC events in steel storage tanks under seismic loading
No full textThe damage states in a storage tank subjected to seismic
loading can induce loss of containment (LOC) with possible
consequences (fire, explosion, etc..) both for the surrounding
units and people. This aspect is particularly crucial for the
Quantitative Risk Analysis (QRA) of industrial plants subjected
to earthquakes. Classical QRA methodologies are based on
standard LOC conditions whose frequency of occurrence is
mainly related to technological accident rather than natural
events and are thus useless. Therefore, it is evident the necessity
of establishing new procedures for the evaluation of the
frequencies of occurrence of LOC events in storage tanks when
subjected to an earthquake.
Consequently, in this work a simple procedure founded on a
probabilistic linear regression-based model is proposed, which
uses simplified numerical models typically adopted for the
seismic response of above ground storage tanks. Based on a set
of predetermined LOC events (e.g. damage in the pipes, damage
in the nozzles, etc..), whose probabilistic relationship with the
local response (stress level, etc..) derives from experimental
tests, the probabilistic relationship of selected response
parameters with the seismic intensity measure (IM) is
established. As result, for each LOC event, the cloud analysis
method is used to derive the related fragility curve
Seismic vulnerability mitigation of liquefied gas tanks using concave sliding bearings
No full textThe aim of this paper is to evaluate the effectiveness of a concave sliding bearing system for the seismic protection of liquefied gas storage tanks through a seismic fragility analysis. An emblematic case study of elevated steel storage tanks, which collapsed during the 1999 İzmit earthquake at Habas Pharmaceutics plant in Turkey, is studied. Firstly, a fragility analysis is conducted for the examined tank based on a lumped-mass stick model, where the nonlinear shear behaviour of support columns is taken into account by using a phenomenological model. Fragility curves in terms of an efficient intensity measure for different failure modes of structural components demonstrate the inevitable collapse of the tank mainly due to insufficient shear strength of the support columns. A seismic isolation system based on concave sliding bearings, which has been demonstrated a superior solution to seismically protect elevated tanks, is then designed and introduced into the numerical model, accounting for its non-linear behaviour. Finally, a vulnerability analysis for the isolated tank is performed, which proves a high effectiveness of the isolation system in reducing the probability of failure within an expected range of earthquake intensity levels
Refined and simplified numerical models of an isolated old highway bridge for PsD testing
No full textSeismic fragility analysis of steel storage tanks
No full textEarthquakes 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
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