Numerical modelling of ground-tunnel support interaction using bedded-beam-spring model with fuzzy parameters

The study of the ground-tunnel interaction by introducing a predetermined degree of variation (fuzziness) in some parameters of the chosen model is presented and discussed. This research comes from the consideration that tunnel model parameters and geometry are usually affected by a degree of uncertainty, mainly due to construction imprecision and the great variability of rock mass properties. The research has been developed by using the fuzzy set theory assuming that three model parameters are affected by a certain amount of uncertainty (defined by the so-called membership functions). The response of the numerical model is calculated by solving the fuzzy equations for different shapes of the membership functions. In order to investigate the effects of some model parameters, and to provide a simple procedure and tool for the designers, a study on the effect of tunnel boundary conditions, based on a fuzzy model, has been carried out using a simple but well known and widely used design method such as the bedded-beam-spring mode

Uncertainty and Intelligence in Computational Stochastic Mechanics

Classical structural reliability assessment techniques are based on precise and crisp (sharp) definitions of failure and non-failure (survival) of a structure in meeting a set of strength, function and serviceability criteria. These definitions are provided in the form of performance functions and limit state equations. Thus, the criteria provide a dichotomous definition of what real physical situations represent, in the form of abrupt change from structural survival to failure. However, based on observing the failure and survival of real structures according to the serviceability and strength criteria, the transition from a survival state to a failure state and from serviceability criteria to strength criteria are continuous and gradual rather than crisp and abrupt. That is, an entire spectrum of damage or failure levels (grades) is observed during the transition to total collapse. In the process, serviceability criteria are gradually violated with monotonically increasing level of violation, and progressively lead into the strength criteria violation. Classical structural reliability methods correctly and adequately include the ambiguity sources of uncertainty (physical randomness, statistical and modeling uncertainty) by varying amounts. However, they are unable to adequately incorporate the presence of a damage spectrum, and do not consider in their mathematical framework any sources of uncertainty of the vagueness type. Vagueness can be attributed to sources of fuzziness, unclearness, indistinctiveness, sharplessness and grayness; whereas ambiguity can be attributed to nonspecificity, one-to-many relations, variety, generality, diversity and divergence. Using the nomenclature of structural reliability, vagueness and ambiguity can be accounted for in the form of realistic delineation of structural damage based on subjective judgment of engineers. For situations that require decisions under uncertainty with cost/benefit objectives, the risk of failure should depend on the underlying level of damage and the uncertainties associated with its definition. A mathematical model for structural reliability assessment that includes both ambiguity and vagueness types of uncertainty was suggested to result in the likelihood of failure over a damage spectrum. The resulting structural reliability estimates properly represent the continuous transition from serviceability to strength limit states over the ultimate time exposure of the structure. In this section, a structural reliability assessment method based on a fuzzy definition of failure is suggested to meet these practical needs. A failure definition can be developed to indicate the relationship between failure level and structural response. In this fuzzy model, a subjective index is introduced to represent all levels of damage (or failure). This index can be interpreted as either a measure of failure level or a measure of a degree of belief in the occurrence of some performance condition (e.g., failure). The index allows expressing the transition state between complete survival and complete failure for some structural response based on subjective evaluation and judgment

Influence of the Tunnel Shape on Shotcrete Lining Stresses

Tunnel excavation is frequently carried out in rock masses by the drill and blast method and the final shape of the tunnel boundary can be irregular due to overbreaks. In order to investigate the effects of overbreaks a study of the effect of tunnel boundary irregularity has been carried out. This is done developing a computational tool able to take into account fuzzy variables (i.e., thickness of the beams of the bedded spring approach used for the model). The obtained results show that irregularity effects should be considered when a shotcrete lining is used as the final tunnel lining (for the case where the tunneling procedure does not permit a smooth surface to be obtained). This is crucial to obtain a durable linin

Performance-based seismic design of steel structures accounting for fuzziness in their joint flexibility

This paper presents a performance-based earthquake engineering framework to explicitly take into account fuzziness in the design parameters, with application to steel structures. Semi-rigidity of column-to-foundation and beam-to-column connections is considered as a relevant example of design parameters that can be conveniently modelled using fuzzy variables. Without lack of generality, their fixity factors are described by means of triangular membership functions, fully defined by lower and upper values of admissibility and their most likely value, i.e. their reference value. For demonstration purposes, the procedure is applied to analyse two different case studies, namely a 5-storey single-bay plane frame and an industrial 3D modular structure. The analyses are performed accounting for the fuzziness of the connections, which is then propagated onto representative engineering demand parameters, within a general performance-based design (PBD) approach

Advanced Approaches Applied to Materials Development and Design Predictions

This thematic issue on advanced simulation tools applied to materials development and design predictions gathers selected extended papers related to power generation systems, presented at the XIX International Colloquium on Mechanical Fatigue of Metals (ICMFM XIX), organized at University of Porto, Portugal, in 2018. In this issue, the limits of the current generation of materials are explored, which are continuously being reached according to the frontier of hostile environments, whether in the aerospace, nuclear, or petrochemistry industry, or in the design of gas turbines where efficiency of energy production and transformation demands increased temperatures and pressures. Thus, advanced methods and applications for theoretical, numerical, and experimental contributions that address these issues on failure mechanism modeling and simulation of materials are covered. As the Guest Editors, we would like to thank all the authors who submitted papers to this Special Issue. All the papers published were peer-reviewed by experts in the field whose comments helped to improve the quality of the edition. We also would like to thank the Editorial Board of Materials for their assistance in managing this Special Issue

A holistic approach to assessment of value of information (VOI) with fuzzy data and decision criteria.

The research presented in this thesis integrates theories and techniques from statistical analysis and artificial intelligence, to develop a more coherent, robust and complete methodology for assessing the value of acquiring new information in the context of the oil and gas industry. The classical methodology for value of information assessment has been used in the oil and gas industry since the 1960s, even though it is only recently that more applications have been published. It is commonly acknowledged that, due to the large number of data acquisition actions and the capital investment associated with it, the oil and gas industry is an ideal domain for developing and applying value of information assessments. In this research, three main gaps in the classical methodology for value of information are identified and addressed by integrating three existing techniques from other domains. Firstly, the research identifies that the technique design of experiments can be used in value of information for providing a holistic assessment of the complete set of uncertain parameters, selecting the ones that have the most impact on the value of the project and supporting the selection of the data acquisition actions for evaluation. Secondly, the fuzziness of the data is captured through membership functions and the expected utility value of each financial parameter is estimated using the probability of the states conditioned to the membership functions - in the classical methodology, this is conditioned to crisp values of the data. Thirdly, a fuzzy inference system is developed for making the value of information assessment, capturing the decision-making human logic into the assessment process and integrating several financial parameters into one. The proposed methodology is applied to a case study describing a value of information assessment in an oil field, where two alternatives for data acquisition are discussed. The case study shows how the three techniques can be integrated within the previous methodology, resulting in a more complete theory. It is observed that the technique or design of experiments provides a full identification of the input parameters affecting the value of the project, and allows a proper selection of the data acquisition actions. In the case study, it is concluded that, when the fuzziness of the data is included in the assessment, the value of the data decreases in comparison with the case where data are assumed to be crisp. This result means that the decision concerning the value of acquiring new data depends on whether the fuzzy nature of the data is included in the assessment, and on the difference between the project value with and without data acquisition. The fuzzy inference system developed for this case study successfully follows the logic of the decision maker and results in a straightforward system to aggregate decision criteria. Sensitivity analysis of the parameters of two different membership functions is made, reaching consistent results in both cases

Towards an Operational Framework for Financial Stability: "Fuzzy" Measurement and its Consequences

Over the last decade or so, addressing financial instability has become a policy priority. Despite the efforts made, policymakers are still a long way from developing a satisfactory operational framework. A major challenge complicating this task is the “fuzziness” with which financial (in)stability can be measured. We review the available measurement methodologies and point out several weaknesses. In particular, we caution against heavy reliance on the current generation of macro stress tests, arguing that they can lull policymakers into a false sense of security. Nonetheless, we argue that the “fuzziness” in measurement does not prevent further progress towards an operational framework, as long as it is appropriately accounted for. Crucial features of that framework include: strengthening the macroprudential orientation of financial regulation and supervision; addressing more systematically the procyclicality of the financial system; relying as far as possible on automatic stabilizers rather than discretion, thereby lessening the burden on the real-time measurement of financial stability risks; and setting up institutional arrangements that leverage the comparative expertise of the various authorities involved in safeguarding financial stability, not least financial supervisors and central banks.

Factor Analysis vs. Fuzzy Sets Theory: Assessing the Influence of Different Techniques on Sen's Functioning Approach

This paper explores a couple of specific operational interpretations of Sen's approach in view of assessing the extent to which the results originated by the implementation of Sen's concepts are influenced by the choice of the specific technique. By means of a survey based on a representative sample of Belgian individuals, seven achieved functioning's are identified via each technique and subsequently confronted. To structure the information and to facilitate comparisons, standard multivariate analysis is performed, while at the same time considering in more detail the sub-group of the most deprived individuals. In this way, a substantial accordance - yet no perfect equivalence - is uncovered in the general patterns of functionings' achievements.

Factor Analysis vs Fuzzy Sets Theory: Assessing the Influence of Different Techniques on Sen's Functioning Approach.

This paper explores a couple of specific operational interpretations of Sen's approach in view of assessing the extent to which the results originated by the implementation of Sen's concepts are influenced by the choice of the specific technique. By means of a survey based on a representative sample of Belgian individuals, seven achieved functioning's are identified via each technique and subsequently confronted. To structure the information and to facilitate comparisons, standard multivariate analysis is performed, while at the same time considering in more detail the sub-group of the most deprived individuals. In this way, a substantial accordance - yet no perfect equivalence - is uncovered in the general patterns of functioning's' achievements.

Aging structure life prediction and reliability assessment

Confront with the serious aging problem in aircraft structure field, the profession was tasked to unveil the mysterious in the mechanism of aging. In decades, many endeavours were put into different subjects such as, fatigue and crack calculation, corrosion analysis, reliability evaluation, life prediction, structure monitor and protection, structure repair, etc. In an effort of developing a reasonable model for life prediction and reliability evaluation, a wide range of topics in the field of aging structure reliability are reviewed. Many existing methods and tools are carefully studied to distinguish the advantages, disadvantages and the special application. With consideration of corrosion fatigue life, and based on the data obtained through investigating service status of the aging aircraft, a fuzzy reliability approach is proposed and presented. Initially, the thesis presents the literature review in the field, introducing the well-established theories and analysis tools of reliability and points out how such these methods can be used to assess the life and reliability of aging structure. Meanwhile, some characteristic parameters and distributions, as well as some crucial calculation formulations, procedures for aging aircraft reliability/risk analysis are given. Secondly, mathematical models are established to evaluate the initial crack size and to assess both randomness and fuzziness of the variables, which also successfully work out the probability of survival of existing structures over a time period and predict the operation time under specific reliability requirement. As a practical approach to the reliability of aging aircraft structure, example is presented and evaluated. While conduct the calculation, a few programs based on FORTRAN code are developed to solve the none-linear equation, to work out the multi dimension integration and to simulate the survival probability. The crack life prediction software AFGROW is selected for comparison of the calculation results, which also shows the appropriate accuracy of the established model. As conclusion, the effects of some variables including fuzzy factors on reliability and life of aging aircraft structure are finally discussed. It is apparent that the confines of the model are existing as fact because of the huge assumption of the parameters input and model uncertainties. Suggestions on further prospective research are proposed respectively