Structural Safety Analysis Research Articles

A robust risk assessment methodology for safety analysis of marine structures under storm conditions

Accidents involving vessels and/or offshore structures (henceforth referred to as marine structures) may pose high financial, environmental and fatality risk. To effectively manage these risks a methodical approach is required to model accident load and the stochastic behaviour of the marine structure that are arising from storm effects. This paper introduces a proactive framework that identifies and considers all the initial relevant risks. Compared to the conventional approaches that rely on precursor data for accident modelling, the developed methodology utilizes the critical stochastic variables directly from the hydrodynamic analysis of the floating structure. For this purpose, a novel numerical model is proposed to replicate a storm based on Endurance Wave Analysis (EWA) method. This approach reduces the computational cost (time and load) of the simulations. The critical stochastic variables are subsequently used in Bayesian Network (BN) to develop the risk model. The EWA and BN based integrated methodology assists in better understanding of accident causation and associated risk in changing operational conditions. The application of the methodology is demonstrated through a Floating Storage Unit (FSU) experiencing capsizing scenario.

Anomaly detection with the Switching Kalman Filter for structural health monitoring

Detecting changes in structural behaviour, i.e. anomalies over time is an important aspect in structural safety analysis. The amount of data collected from civil structures keeps expanding over years while there is a lack of data-interpretation methodology capable of reliably detecting anomalies without being adversely affected by false alarms. This paper proposes an anomaly detection method that combines the existing Bayesian Dynamic Linear Models framework with the Switching Kalman Filter theory. The potential of the new method is illustrated on the displacement data recorded on a dam in Canada. The results show that the approach succeeded in capturing the anomalies caused by refection work without triggering any false alarms. It also provided the specific information about the dam's health and conditions. This anomaly detection method offers an effective data-analysis tool for Structural Health Monitoring.

Integrated structural safety analysis of San Francisco Master Gate in the Fortress of Almeida

ABSTRACTAfter more than 300 years of being exposed to human and nature actions the Master Gate of San Francisco in Almeida, Portugal, has sustained visible extended damage. Although its importance, as a historical monument, is undeniable, no attempts have been done so far to determine its level of safety. In this article, several models are developed in order to achieve this goal. A brief description of the Gate’s history is presented followed by a summary of the inspection and diagnosis procedures employed in this study and the results obtained from them. Later, the type of numerical models selected are discussed as well as the methodologies used to represent damage. Finally results from the numerical models are presented in a first attempt to identify the safety level of this historic construction. Results indicate that although the structure has lost a great percentage of its original capacity is still safe.

Effect of Different Cold Working Plastic Hardening on Mechanical Properties of 316L Austenitic Stainless Steel

It is the important foundation data that the material mechanics properties parameters in the important structure integrity evaluation and safety analysis. Since cold working will change the mechanical parameters of the local region material, and these local regions often play an important role in structural integrity analysis. To obtain the preliminary data of the mechanical parameters with different cold deformation, the relation of the cold deformation and mechanical parameters of 316L austenitic stainless steel is analyzed by combining the theoretical analysis, numerical simulation and uniaxial tensile testing in this paper. The investigated results indicate that the cold working will increase the yield stress of the material to some extent, but has little effect on the reduction factor. The approach proposed in this paper could be used to preliminary estimate the mechanical properties parameters of materials subjected to cold working in the important engineering structures.

Inverse problems in structural safety analysis with combined probabilistic and non-probabilistic uncertainty models

In problems of structural safety analysis, depending upon the nature and extent of availability of empirical data, uncertainties could be quantified by using probabilistic and/or non-probabilistic models. The options for non-probabilistic representations include intervals, convex functions, and (or) fuzzy variable models. We consider a few inverse problems of structural safety analysis aimed at the determination of system parameters to ensure a target level of safety and/or to minimize a cost function for problems involving combined probabilistic and non-probabilistic uncertainty modeling. The treatment of this problem calls for combining methods of uncertainty analysis with finite element structural modeling and numerical optimization tools. Development of load and resistance factor design format, in problems with combined uncertainty models, is also presented. We employ super-ellipsoid based convex function models for representing non-probabilistic uncertainties. The target safety levels are taken to be specified in terms of indices defined in standard space of uncertain variables involving standard normal random variables and/or unit hyper-spheres. A class of problems amenable for exact solutions is identified and a general procedure for dealing with more general problems involving nonlinear performance functions is developed. Illustrations include studies on inelastic frame with uncertain properties. Accompanying supplementary material contains additional illustrations.

Study on Design and Test of Composite WIG Vehicle Considering on Impact Loading

This study proposed an example on preliminary structural design including trade-off study and design evaluation such as structural safety and stability analysis of a 20-seat composite WIG craft using the netting rule and the rule of mixture and a commercial FEM tool. The structural configuration of the wing adopted the skin-spar semi-monocoque type structure with foam sandwich, and the fuselage also used the semi-monocoque type structure with the skin to carry shear flow, the stringers to carry bending moments and the ring frames to carry local loads under consideration of various design local load cases. The used materials were Carbon/Epoxy (UD) for wing spar flanges and fuselage stringers and ring frames, Carbon/Epoxy (Fabric) for fuselage skins, the sandwich with Carbon/Epoxy face sheet (Fabric) and Al honeycomb core for the fuselage floor, and the sandwich with Carbon/Epoxy face sheet (UD) and Urethane foam core for wing skins and spar webs. Through the structural analysis, the structural safety and stability were confirmed.

Structural Safety Analysis of FPWEC During Sea Transportation

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일부타정식 케이블 시스템 장경간 사장교의 시공 중 동적 안전성 분석

일부타정식 케이블 시스템 장경간 사장교의 시공 중 동적 안전성 분석

Stochastic modelling and prediction of fatigue crack propagation using piecewise-deterministic Markov processes

Fatigue crack propagation is a stochastic phenomenon due to the inherent uncertainties originating from material properties, environmental conditions and cyclic mechanical loads. Stochastic processes thus offer an appropriate framework for modelling and predicting crack propagation. In this paper, fatigue crack growth is modelled and predicted by a piecewise-deterministic Markov process associated with deterministic crack laws. First, a regime-switching model is used to express the transition between the Paris regime and rapid propagation that occurs before failure. Both regimes of propagation are governed by a deterministic equation whose parameters are randomly selected in a finite state space. This one has been adjusted from real data available in the literature. The crack growth behaviour is well-captured and the transition between both regimes is well-estimated by a critical stress intensity factor range. The second purpose of our investigation deals with the prediction of the fatigue crack path and its variability based on measurements taken at the beginning of the propagation. The results show that our method based on this class of stochastic models associated with an updating method provides a reliable prediction and can be an efficient tool for safety analysis of structures in a large variety of engineering applications. In addition, the proposed strategy requires only little information to be effective and is not time-consuming.

Safety analysis of structures with probability and evidence theory

In safety analysis of structures, classical probabilistic analysis has been a popular approach in engineering. However, it is not always to obtain sufficient information to model all uncertain parameters of structures system by probability theory, especially at early stage of design. Under this circumstance, probability theory (used to model random uncertainty) combined with evidence theory (used to model epistemic uncertainty) may be utilized in safety analysis of structures. This paper proposed a novel method for safety analysis of structures based on probability and evidence theory. Firstly, Bayes conversion method is used as the way for precision of evidence body, and the mean and variance of epistemic uncertain variables is defined. Then epistemic uncertainty variables is transformed to normal random variables by reflection transformation method, and the checking point method (J-C method) is used to solve most probability point and reliability. A numerical example and two engineering examples are given to demonstrate the performance of the proposed method. The results show both precision and computational efficiency of the method is high. Moreover, the proposed method provides basis for reliability-based optimization with the hybrid uncertainties.

Design, development and tests of a compact thermofluid system

To mitigate temperature overshoot and dissipate highly concentrated heat from high-power electronic components, it is important to develop an ultrathin vapor chamber/heat spreader to fit in a compact 3D electronic system. As a semiconductor material, silicon is highly thermal conductive, micromachinable and process-compatible with microelectronic manufactures. Thus, a silicon based vapor chamber (SVC) can be directly integrated with microelectronic devices to achieve hot spot cooling, without introducing an additional thermal interface. This article reports the development of SVC, stating from analysis of structural safety, followed by numerical simulations of the liquid and vapor flows. Advanced multiscale wick structures are implemented to balance the heat and mass transports of high heat flux under a gravitational force. On these bases, SVC with structural reinforcement of a 13 × 8 pillar array is developed through a triple bonding approach. The successful development of the SVCs results in a large scale (50 mm × 70 mm) and ultrathin (1 mm thick) phase change heat transfer device, with the effective density less than 1.5 × 103 kg/m3. Using water as the operating fluid, we experimentally demonstrate a high effective thermal conductivity over 10,000 W/m⋅K in both 1D and 2D heat transfer modes.

Interval process model and non-random vibration analysis

This paper develops an interval process model for time-varying or dynamic uncertainty analysis when information of the uncertain parameter is inadequate. By using the interval process model to describe a time-varying uncertain parameter, only its upper and lower bounds are required at each time point rather than its precise probability distribution, which is quite different from the traditional stochastic process model. A correlation function is defined for quantification of correlation between the uncertain-but-bounded variables at different times, and a matrix-decomposition-based method is presented to transform the original dependent interval process into an independent one for convenience of subsequent uncertainty analysis. More importantly, based on the interval process model, a non-random vibration analysis method is proposed for response computation of structures subjected to time-varying uncertain external excitations or loads. The structural dynamic responses thus can be derived in the form of upper and lower bounds, providing an important guidance for practical safety analysis and reliability design of structures. Finally, two numerical examples and one engineering application are investigated to demonstrate the feasibility of the interval process model and corresponding non-random vibration analysis method.

Risk Assessment of Safety Analysis of Nuclear Power Plant Structures in the Earthquake Active Zones

Risk Assessment of Safety Analysis of Nuclear Power Plant Structures in the Earthquake Active Zones

Risk Assessment of Safety Analysis of NPP Structures due to Earthquake Events

This paper presents the probabilistic safety assessment of nuclear power plant (NPP) in Slovakia due to earthquake event. The experiences from the deterministic and probabilistic seismic analyses of the structure resistance are mentioned. On the base of the geophysical and seismological monitoring of locality the peak ground acceleration was defined for the return period 104 years using the Monte Carlo simulations. The synthetic spectrum compatible accelerograms generated in program COMPACEL are presented in comparison with requirements of ASCE4/98 standard.

Finite element analysis for structural evaluation of marine loading arm

This paper describes a structural safety analysis of a marine loading arm that transfers liquids or gases to and from tank ships or cargo vessels. The structural design of the marine loading arm was performed in accordance with OCIMF. Stresses for ten load conditions considered in this study were drawn by finite element analysis, and were compared with the allowable stresses required by OCIMF in order to determine the design appropriateness of the marine loading arm.

Phase Field Approximation of Dynamic Brittle Fracture

AbstractThe numerical assessment of fracture has gained importance in fields like the safety analysis of technical structures or the hydraulic fracturing process. The modelling technique discussed in this work is the phase field method which introduces an additional scalar field. The smooth phase field distinguishes broken from undamaged material and thus describes cracks in a continuum. The model consists of two coupled partial differential equations ‐ the equation of motion including the constitutive behaviour of the material and a phase field evolution equation. The crack growth follows implicitly from the solution of this system of PDEs. The numerical solution with finite elements can be accelerated with an algorithm that performs computationally extensive tasks on a graphic processing unit (GPU). A numerical example illustrates the capability of the model to reproduce realistic features of dynamic brittle fracture. (© 2014 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Non-Linear Static Pushover Analysis of Real Life Reinforced Concrete Frame with ATENA 3-D Program

The non-linear static analysis (push over analysis) provides good understanding of seismic behavior of structures. Pushover analysis produces pushover curve which consists of capacity spectrum. In the current paper, the non-linear response of four storeyed RC frame under the pushover loading (monotonically incremental load) has been obtained to study the response and load-carrying capacity of RC frame using non-linear finite element analysis. An analysis model for four storeyed RC frame using software ATENA, a computer program using stress analysis with finite element method, is presented. The results obtained from FE analysis are compared with the experimental data for four storeyed RC frame, at the same location as used in experimental test. The correctness of the finite element model is assessed by the comparison with experimental results which are to be in good agreement. The pushover curves (base shear versus displacement curves) obtained from finite element analysis agree with the experimental results in linear and non- linear range. The concrete has been the most preferred construction material for many decades due to its wonderful properties There are a variety of factors which are responsible for the degradation of RC structures such as increasing load, deterioration of steel due to corrosion, seismic forces, environmental degradations and accidental impacts on the structure. The increase in height of modern structures is intimately related with the extent and impact of disaster in terms of human and economical loss in the occurrence of structural failure. The existing structures can also become seismically deficient since design code requirements are constantly upgraded due to advancement in engineering knowledge. In India most of the buildings constructed over past two decades are seismically inadequate due to lack of knowledge regarding seismic behavior of structures. Hence a careful and systematic structural safety analysis becomes compulsory. To evaluate RC structures against failure an accurate estimation of the ultimate load is necessary and the prediction of the load-deformation behavior of the structure throughout the range of linear and non-linear response is advantageous. To obtain a global mechanism for the structure with a ductile behavior the non-linear analysis is required to be carried out. Nowadays the statically nonlinear method called pushover method, is becoming a popular tool for seismic performance evaluation of new and existing structures. The pushover analysis is a nonlinear static analysis for a reinforced concrete framed structure subjected to lateral loading. The gravity loads are applied and then lateral loading is applied first in X- direction starting at the end of the gravity push and next in y- direction again starting at the end of gravity push(1). The pushover analysis provides ample information on seismic demands imposed by the design ground motion on the structural system and its components. The objective of pushover analysis is to evaluate the expected performance of structural systems by estimating performance of a structural system by estimating its strength and deformation demands in design earthquakes by means of static inelastic analysis, and comparing these demands to available capacities at the performance levels of interest. The inelastic static pushover analysis can be viewed as a method for predicting seismic force and deformation demands, which accounts in an approximate manner for the redistribution of internal forces that no longer can be resisted within the elastic range of structural behavior (2).

Fracture Toughness of Ferritic Steels: Lower Bounds and their Implications on Testing and Application

For physical reasons fracture toughness KJc of ferritic steels in the brittle-to-ductile transition regime is affected by a pronounced scatter, which requires statistical methods to be applied for evaluation of test results as well as for application in safety analysis of structures. For this purposes the probabilistic Master-Curve-approach according to ASTM E1921 is often used. However, for engineering purposes like a screening safety analysis of a defect-containing component it is usually preferable to use a deterministic lower bound. However, within the framework of ASTM-standards there is no possibility to determine KIc experimentally. So KIc needs to be determined indirectly from the reference temperature T0. In the present paper it is shown how lower bounds of fracture toughness – either plane strain KIc for large components or thickness-dependent KJc for smaller ones - can be derived from T0, and how the latter can be determine with sufficient accuracy from one or a few KJc values.

Comprehensive Analysis of Structural Safety and Durability for Aero-Engine

In order to meet the airworthiness requirements (FAR33.70) of large commercial aero-engines, a new approach of probabilistic risk assessment linked durability is presented, and aiming at the issue of low-failure probabilities of key aero-engine structures, probabilistic risk assessment based on the Monte Carlo Radius-Outside Sampling (MCROS) in combination with the Kriging is used, then random factors such as the material, loading and environment can be considered in the given method. Example of probabilistic risk assessment based on fatigue for lower pressure compressor disk of aero-engine demonstrates the applicability, versatility and accuracy of the approach.

Structural Safety Analysis Based on Seismic Service Conditions for Butterfly Valves in a Nuclear Power Plant

The structural integrity of valves that are used to control cooling waters in the primary coolant loop that prevents boiling within the reactor in a nuclear power plant must be capable of withstanding earthquakes or other dangerous situations. In this study, numerical analyses using a finite element method, that is, static and dynamic analyses according to the rigid or flexible characteristics of the dynamic properties of a 200A butterfly valve, were performed according to the KEPIC MFA. An experimental vibration test was also carried out in order to verify the results from the modal analysis, in which a validated finite element model was obtained via a model-updating method that considers changes in the in situ experimental data. By using a validated finite element model, the equivalent static load under SSE conditions stipulated by the KEPIC MFA gave a stress of 135 MPa that occurred at the connections of the stem and body. A larger stress of 183 MPa was induced when we used a CQC method with a design response spectrum that uses 2% damping ratio. These values were lower than the allowable strength of the materials used for manufacturing the butterfly valve, and, therefore, its structural safety met the KEPIC MFA requirements.