1,720,953 research outputs found
Propagation and band width of smeared cracks
No full textThe crack band approach (in the smeared crack concept) is widely used for the modeling of concrete fracture and is an important analysis technique within advanced engineering. However, the simulations can be impeded by mesh-induced directional bias. Cracks prefer to propagate along continuous mesh lines, which causes a dependency of the numerical results on the structure and orientation of the finite element discretization. In this PhD research, two different enhancements of the crack band approach are proposed to reduce the mesh bias as much as possible. The performance of both enhancements is investigated by simulations of plain concrete fracture tests and a shear critical reinforced concrete beam without shear reinforcement. Both enhancements increase the accuracy of the crack band approach in the smeared crack concept and simultaneously preserve its relative simplicity. Hence, they can be valuable for engineering practice, supporting reliable predictions of ultimate load capacities, failure mechanisms and post-peak behaviors of quasi-brittle reinforced concrete structures.Structural EngineeringCivil Engineering and Geoscience
Sequentially linear modelling of combined tension/compression failure in masonry structures
No full textThe modelling of brittle fracture is essential for the assessment of structural safety. It remains a challenge due to sharp material softening after realization of the material strength. Standard nonlinear finite element analysis techniques using incremental-iterative solution procedures have been adapted to deal with the sharp softening curves associated with brittle materials, but convergence difficulties have stimulated the development of alternative modelling methods. The sequentially linear analysis method is an attractive alternative approach, since it is driven by increments of damage instead of increments of displacements, force or time. Consequently, this non-iterative procedure circumvents the aforementioned convergence difficulties. This method is still in its development stage and needs to be augmented, verified with tests and validated with experimental results with respect to multiple situations. In this thesis the recent sequentially linear analysis software is verified and combined tension-compression failure is validated with the aid of a masonry deep wall-frame structure.Structural MechanicsStructural EngineeringCivil Engineering and Geoscience
C¹ - continuous crack propagation for mixed-mode fracture problems
No full textStructural EngineeringCivil Engineering and Geoscience
A testing preocedure for the evaluation of directional mesh bias
No full textThis paper presents a dedicated numerical test that enables to assess the directional mesh bias of constitutive models in a systematic way. The test makes use of periodic boundary conditions, by which strain localization can be analyzed for different mesh alignments with preservation of mesh uniformity and with exclusion of boundary disturbances. After an exploratory study of the proposed test, the test is demonstrated by applying it to the classical and still widely used crack band model. An analysis series is performed on five meshes with different alignments. The meshes consist of squared quadrilateral elements with varying interpolation function and numerical integration scheme. From the results it can be concluded that the test identifies a significant mesh-induced directional bias.Structural EngineeringCivil Engineering and Geoscience
Extension and Verification of Sequentially Linear Analysis to Solid Elements
No full textWhen analyzing three-dimensional problems with nonlinear finite element analysis (NLFEA) often problems are encountered such as bifurcation and divergence of the solution. In particular, cases subjected to tension softening tend to encourage the emergence of multiple equilibrium paths. In order to overcome these problems the Sequentially Linear Analysis (SLA) method has been developed for three-dimensional solid elements. SLA is an alternative for incremental-iterative solution schemes to model the nonlinear fracture behavior of quasi-brittle materials. It is an attractive method since it avoids the well known convergence and bifurcation problems that are often encountered when using incremental-iterative schemes such as Newton-Raphson. SLA uses a series of linear analyses to model the nonlinear behavior of the structure. By directly specifying a damage increment in each linear analysis, extensive iterations within the load or displacement increment can be avoided. The main objective of this research was to see how the Sequentially Linear Analysis approach could be extended to solid elements, so that it could be used for three-dimensional fracture problems as well. Although three-dimensional geometries such as masonry structures have been analyzed before using SLA, it was always restricted to two-dimensional finite elements only (shell elements). Therefore, first a theoretical constitutive model for three-dimensional stress-strain states has been developed that served as the starting point. Implementation in DIANA was the major second step from which the third and last step could be started: the verification on various fictive and real cases. A single element pull test was used to solve programming errors, whereas the notched beam offered the possibility to check how the newly developed SLA-code would perform for larger models. Both cases showed excellent agreement with the experiment. However, most attention was dedicated to the verification and physical interpretation of a real reinforced concrete slab. The results were critically evaluated, interpreted and compared to results from the experiment and the incremental-iterative Newton-Raphson method. It was concluded that the Sequentially Linear Analysis is able to properly capture the quasi-brittle behavior of the reinforced concrete slab. Especially in comparison to the three-dimensional Newton-Raphson results, SLA turned out to be more robust and accurate.Structural EngineeringCivil Engineering and Geoscience
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Crack pattern observations to finite element simulation: An exploratory study for detailed assessment of reinforced concrete structures
No full textUncertainties regarding structural safety of reinforced concrete structures may warrant a need for a detailed assessment. A detailed assessment using nonlinear finite element analysis is one of the alternatives which could help in decision-making about maintaining, upgrading or even demolishing and rebuilding of the structure. A reliable assessment should account for the existing damage in the structure, which may cause re-distribution of stresses within the structure, giving rise to unexpected failure modes. The existing approaches in nonlinear finite element analysis which account for the effect of already undergone damage in concrete, pose a number of limitations which either makes structural analysis ambitious or the uncertainty of concrete damage is not effectively accounted for. An alternative approach is adopted in this thesis, which is phenomenological and probabilistic in nature. Existing damage in concrete is conceived as a statistical field, which can be input into a finite element model, such that the existence of damage is taken as the starting point of the structural analysis. Focusing on indications of damage on the surface of concrete, i.e. crack patterns, an exploratory methodology based on image analysis is developed, to account for information obtained from crack pattern observation into nonlinear finite element analysis of reinforced concrete structures. The methodology is implemented on MATLAB and validated on damaged experimental specimens. Results of the computational analyses indicate good efficiency in predicting residual load carrying capacities and failure modes, alongside insightful numerical crack patterns. Through a critical examination of the obtained results and reflection upon the assumptions and simplification made in the methodology, recommendations for future research are provided
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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