1,721,063 research outputs found
1st International Summer School on Smart Structures: New Technologies from a Civil and Mechanical Engineering Perspective
No full textEditorial for the special topic
No full textThe scientific community is currently paying particular attention on the effects of Na-Tech events to industrial facilities for the important economic and social impact that these events can entail on the society. In fact, effective risk analysis is critical for industrial plants to assure the necessary safety level as clearly demonstrated by very recent events as the 2011 Tohoku Earthquake. Nevertheless, the effort in developing new techniques is being more and more important as clearly proven by the rapid increasing of the contributions on this topic. This special topic, titled "Na-tech risk assessment methodologies and mitigation solutions in the process industries", promoted by the Guest Editors: Oreste S. Bursi, Fabrizio Paolacci and Tomoyo Taniguchi, within the Seismic Engineering Technical Committee of the ASME Pressure Vessel and Piping Division, is aimed to bring together the latest methodologies and techniques for a reliable estimation of Na-Tech risk in process plants that represents one of the most diffused hazards in industrial facilities. Contributions were called from researchers and industry professionals, strongly active in this area. A total of ten papers were accepted that cover many of the key topics related to Na-Tech events and consequences in Industrial Facilities
Performance-based analysis of coupled support structures and piping systems subject to seismic loading
No full textThe prevailing lack of proper and uniform seismic design guidelines for piping systems impels designers to follow standards conceived for other structures, such as buildings. The modern performance-based design approach is yet to be widely adopted for piping systems, while the allowable stress design method is still the customary practice. This paper presents a performance-based seismic analysis of petrochemical piping systems coupled with support structures through a case study. We start with a concept of performance-based analysis, followed by establishing a link between limit states and earthquake levels, exemplifying Eurocode and Italian prescriptions. A brief critical review on seismic design criteria of piping, including interactions between piping and support, is offered thereafter. Finally, to illustrate actual applications of the performance-based analysis, non-linear analyses on a realistic petrochemical piping system is performed to assess its seismic performance
Seismic performance assessment of oil & gas piping systems through nonlinear analysis
No full textPiping systems, a vital part of energy industries, e.g. petrochemical, oil & gas and chemical plants, have been found particularly vulnerable under earthquake loading, as reported in recent publications. During past earthquakes, piping systems and their components suffered significant damages causing severe consequences. Thus, seismic assessment/evaluation of these structures has become an imperative for their proper design to safeguard them against seismic events. Nevertheless, there exists an inadequacy of proper seismic analysis and design rules for petrochemical piping systems, and designers have to follow seismic standards conceived for other structures such as buildings and nuclear plants. Moreover, the modern performance-based design approach is still not widely adopted for piping systems, where the allowable design method is the customary practice. Along these lines, this paper presents a performance-based seismic analysis of petrochemical plants through two case studies. Initially, main issues on seismic analysis and design of industrial piping systems and components are addressed followed by a discussion on the selection of proper seismic inputs. The current allowable stress and strain based seismic verification methods are presented afterward. Then, nonlinear finite element analyses of two typical petrochemical piping systems under modern design earthquake levels are presented. Finally, performance of these piping systems is commented by comparing the maximum stress and strain levels - found from the analyses-with the allowable design values that exhibited a favourable behaviour of the analysed systems under earthquake limit state levels
A time domain procedure for the identification of periodic structures
Full text linkA procedure for the identification of dispersion curves and mechanical characteristics of linear and nonlinear
one-dimensional (1D) periodic structures is proposed herein. The procedure exploits the application of Floquet–
Bloch (F–B) boundary conditions to a reference subsystem (RS) extracted from a mechanical metastructure. The
dispersion curves (frequency vs. wavenumbers) are estimated from the computation of the frequency response
functions (FRFs) of the RS for different wavenumbers in input. The proposed procedure is applied and validated
on various models, including a 1D mass-in-mass system characterized by cubic nonlinear springs. As expected,
the nonlinear system exhibits a distinct dependence on the amplitude of the excitation. In addition, a revised
application of the subspace identification (SI) method is exploited for the identification of hardening-type
nonlinear mechanical characteristics. For the sake of completeness, the identification procedure is also tested
on a waveguide in axial and flexural vibrations. Due to its single output from a measuring cell, and two inputs,
the proposed method is particularly suitable for the experimental characterization of periodic structures.A procedure for the identification of dispersion curves and mechanical characteristics of linear and nonlinear one-dimensional (1D) periodic structures is proposed herein. The procedure exploits the application of Floquet–Bloch (F–B) boundary conditions to a reference subsystem (RS) extracted from a mechanical metastructure. The dispersion curves (frequency vs. wavenumbers) are estimated from the computation of the frequency response functions (FRFs) of the RS for different wavenumbers in input. The proposed procedure is applied and validated on various models, including a 1D mass-in-mass system characterized by cubic nonlinear springs. As expected, the nonlinear system exhibits a distinct dependence on the amplitude of the excitation. In addition, a revised application of the subspace identification (SI) method is exploited for the identification of hardening-type nonlinear mechanical characteristics. For the sake of completeness, the identification procedure is also tested on a waveguide in axial and flexural vibrations. Due to its single output from a measuring cell, and two inputs, the proposed method is particularly suitable for the experimental characterization of periodic structures
A machine learning framework for seismic risk assessment of industrial equipment
No full textThe paper aims to propose a novel machine learning framework for seismic risk assessment of industrial facilities. In this respect, a compound artificial neural network model is employed, which is based on two different artificial neural network models in series. The first artificial neural network is a regression model employed to generate samples of a vector-valued intensity measure. The second one is a classification model that is used to predict structural damage, starting from the outcomes of the first artificial neural network model. The datasets used for training and validation of the two artificial neural networks are based on hazard-consistent accelerograms and numerical analyses that are performed with an efficient finite element model of the structure. The methodology entails a preliminary feature selection phase for the identification of the aforementioned vector-valued of intensity measures that better classifies the damage/no-damage condition of the structure. This phase is implemented through the principal component analysis method. Subsequently, the Metropolis–Hastings algorithm is used to generate samples of a selected intensity measure, feeding the first ANN model. In turn, the chosen features are used as input parameters of the second ANN model to generate samples of damage/no-damage events. Using the two ANN in series, the mean annual frequency of exceeding a specific limit state is derived. The proposed framework is validated using a typical multi-storey steel frame, focusing on the seismic risk assessment of a vertical storage tank located at the first floor of the primary structure. The proposed method exhibits some clear advantages of combining numerical models with ANN techniques, mainly related to: a reduced computational time; the avoidance of any prior information on the probabilistic model of fragility curves; and the use of model-driven data
Performance-based Earthquake Evaluation of a Full-Scale Petrochemical Piping System
Full text linkAssessment of seismic vulnerability of industrial petrochemical and oil & gas piping systems can be performed,
beyond analytical tools, through experimental testing as well. Along this line, this paper describes an experimental test campaign carried out on a full-scale piping system in order to assess its seismic behaviour. In particular, a typical industrial piping system, containing several critical components, such as elbows, a bolted flange joint and a Tee joint, was tested under different levels of realistic earthquake loading. They corresponded to serviceability and
ultimate limit states for support structures as suggested by modern performance-based earthquake engineering standards. The so called hybrid simulation techniques namely, pseudo-dynamic and real time testing with dynamic substructuring, were adopted to perform seismic tests. Experimental results displayed a favorable performance of the piping system and its components; they remained below their yielding, allowable stress and allowable strain limits without any leakage even at the Near Collapse limit state condition for the support structure. Moreover, the favourable comparison between experimental and numerical results, proved the validity of the proposed hybrid techniques alternative to shaking table tests
Role and Application of Testing and Computational Techniques in Seismic Engineering
No full textThe paper presents an evaluation of structural performance in terms of forces and deformations on a 3D two-storey moment-resisting steel-concrete composite structure designed according to Eurocode 8. It was subjected to different pseudo-dynamic tests, simulating earthquakes scaled up to the collapse onset limit state, followed by a final cyclic test. Performance-based seismic design approaches require both experimental and numerical data able to understand the overall behaviour of a structure up to collapse, taking into account material and geometrical nonlinearities, strength degradation, stiffness deterioration and topology changes, such as separation and detachment. In order to pursue these goals two different testing techniques were integrated with non-linear identification and model updating techniques. In particular, the continuous pseudo-dynamic testing and the recent structural behaviour monitoring that employs limited sensors to collect mission-critical data only from the part of a structure that potentially experiences damage - beam-to-column joints and column bases in this case- were employed. It is shown how integration of experimental and numerical techniques can achieve a better damage assessment and demand/capacity spectra design informatio
Seismic fragility analysis of elevated steel storage tanks supported by reinforced concrete columns
No full textThis study aims to investigate the seismic vulnerability of elevated steel storage tanks rested upon reinforced concrete columns through a probabilistic seismic assessment approach. In particular, an elevated steel storage tank which collapsed during the 1999 Kocaeli earthquake in Turkey is considered. In this respect, in order to evaluate the earthquake performance of the tank components during earthquakes, nonlinear time history analyses are conducted on a three-dimensional finite element stick model. Then, probabilistic seismic demand models incorporating uncertainty parameters for the tank components are established using two sets of ground motion records that represent the near-source and far-field characteristics of the earthquakes. Relevant fragility curves which present the most likely damage states of the tank components are derived using both cloud and incremental dynamic analysis methods. The efficiency and sufficiency of different ground motion intensity measures are also evaluated, leading to the conclusion that in analyzed case, the peak ground acceleration demonstrates the best performance among selected intensity measures
A fractional-order model for aging materials: An application to concrete
No full textIn this paper, the hereditariness of aging materials is modeled within the framework of fractional calculus of variable order. A relevant application is made for the long-term behavior of concrete, for which the creep function is evaluated with the aid of Model B3. The corresponding relaxation function is derived through the Volterra iterated kernels and a comparison with the numerically-obtained relaxation function of Model B3 is also reported. The proposed fractional hereditary aging model (FHAM) for concretes leads to a relaxation function that fully agrees with the well-established Model B3. Furthermore, the FHAM takes full advantage of the formalism of fractional-order calculus to yield semi-analytic expressions in terms of material parameters
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