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UBC Theses and Dissertations

Engineering qualitative analysis and its application on fatique design of steel structures Zhou, Ye


Fatigue failures are often encountered in steel structures under heavy cyclic loadings. The advances in Linear Elastic Fracture Mechanics (LEFM) and Finite Element Analysis (FEA) provide engineers and researchers reasonably effective tools for solving fatigue problems. However, most structural and building design codes have not yet taken advantage of advanced theories in modern fracture mechanics due to the complexity of analysis as well as the large quantity of variables involved. The result is that practicing structural engineers are not able to fully utilize state-of-the-art research in fatigue analysis. This thesis considers fatigue problems in structural engineering using outcomes of recent advancements in numerical qualitative analysis. A major result of this research work is an integrated set of software modules for fatigue analysis and evaluation, which have the flexibility to be applied by practicing structural engineers in a variety of situations. The software combine techniques such as interval arithmetic and qualitative reasoning used in the fields of mathematics and information science, and apply them to fatigue analysis. Conventional computation methods generally limit practicing engineers from using complex formulations or considering uncertainties in general. A method is needed that can be implemented regardless of the uncertainty or linearity of the design parameters and their constraints. More exotic methods such as qualitative reasoning provide an effective and sound technique for solving complex and uncertain scenarios. Uncertainties in fatigue designs can be formulated as variables in the application domain and processed by numerical constraint reasoning. The capability of representing design parameters and outcomes in a two-dimensional solution space provides a practical way for engineers to leverage their existing knowledge and experience. The software expresses the results of the analysis in variable ranges and diagrams showing a two-dimensional design space. As a result, the use of qualitative reasoning to define solution trends and ranges can assist in the difficult process of making appropriate engineering assumptions and judgments when carrying out complicated analysis procedures. In addition, interval constraint analysis can be used to derive controlling parameters and design space, therefore giving engineers a good overall understanding of a problem when practical experience is not available.

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