1,720,976 research outputs found
Effects of principal stress rotation on resilient behaviour in rail track foundations
Full text linkThe design of a railway track substructure requires a realistic understanding of the resilient behavior of the underlying track foundation materials, namely, the subballast and subgrade layers. Currently, the best available method of characterizing the resilient behavior of track foundation materials is through the execution of cyclic triaxial tests, although these do not have the ability to impose principal stress rotation (PSR) on test specimens. A previous paper by the authors demonstrated that PSR increases the rate of permanent strain development. This paper reports on the effects of PSR on the resilient behavior of track foundation materials. Four different reconstituted soils selected to represent typical track foundation materials were subjected to undrained cyclic and torsional shear tests in a hollow-cylinder apparatus. It was established that PSR reduces the resilient modulus of the materials compared with cyclic loading without PSR. The effects of PSR as a function of clay content, overconsolidation ratio (OCR), and consolidation regime (isotropic or anisotropic) were also investigated
Effects of Principal Stress Rotation on Permanent Deformation in Rail Track Foundations
No full textA realistic assessment of the whole life cost of rail track foundations requires analysis of the effects of the repeated loadings applied by trains. This paper reports the effects of principal stress rotation (PSR) during cyclic loading on the permanent deformations measured in a series of hollow cylinder tests. The tests were carried out on a number of reconstituted soils selected in order to simulate foundation materials on an existing heavy haul railway line. Typical loadings and track geometry together with dynamic finite-element analyses were used to define representative stress changes to be applied to these soils, which were then tested with and without principal stress rotation during loading. It is shown that principal stress rotation has a significant and deleterious impact on permanent deformation of some materials. Therefore, it is concluded that cyclic triaxial testing, which cannot impose principal stress rotation, will not necessarily give good estimates of the long-term performance of rail track foundations. As PSR cannot be ignored when evaluating permanent displacements of rail track foundations, the use of more appropriate (realistic) testing methods such as the cyclic hollow cylinder or the cyclic simple shear apparatus is require
Measurements of transient ground movements below a ballasted railway line
No full textThis paper presents the results of a detailed investigation into the ground deformations that occur under a railway line during the passage of a train. Four horizontal boreholes were installed at different depths below a ballasted railway track. Ground deformations were measured using geophones at set distances from the centreline of the track within each borehole. The results show vertical displacements reducing with depth, from a maximum at the sleeper. Sleeper displacements are dominated by pairs of bogies at the ends of adjacent wagons (which have a frequency of loading 1 Hz), although the effects of individual bogies (2 Hz) and axles (6 Hz) are also apparent. Higher loading frequencies attenuate with depth so that at a depth of 0·780 m below the sleeper soffit no axles are visible within the displacement data and by a depth of 1·98 m only the combined effect of pairs of adjacent bogies is apparent. In contrast, longitudinal horizontal motion is greatest at a depth of 0·78 m below the sleeper soffit, and the longitudinal horizontal displacements at the sleeper and at a depth of 0·78 m are dominated by the individual axles (?6 Hz). By a depth of 1·98 m, the longitudinal horizontal motion is dominated by the bogie pairs. A dynamic linear-elastic two-dimensional finite element model was developed and validated using the measured displacements
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
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
Metrology of mesoscale ballast particle dynamics using kli-pi
Full text linkDissertation (MEng)--University of Pretoria, 2019.At first glance the operational performance of ballast appears trivial in its simplicity. However, various mechanisms affect the short and long term performance of the ballast and in turn, the response of the track structure, both on a macroscopic scale considering the track structure as an entity and on a discrete particle level or mesoscale. The nature and geometry of the material itself creates difficulty in instrumenting the ballast directly and analytical solutions of the track structure in three dimensions require complex numerical models. The importance of experimental studies to establish the influence of the granular fabric on both the static and quasi-static deformational response of granular materials has been repeatedly highlighted by other researchers. A three-dimensional, half-space model is extremely difficult, if not impossible, to be developed for the theoretical investigation of complex ballast vibrations. This information contributes to the fundamental understanding of mechanical behaviour of granular media.
The proliferation of low cost Micro-Electro-Mechanical Systems (MEMS) has evolved the science of metrology through the introduction of a new class of instruments, known as “smart ballast”, for use in railway and transportation research applications. These instruments are able to quantify both the micro- and macroscopic dynamic response of railway ballast. Such a smart ballast prototype, named Kli-Pi, has been developed by the author. The name is derived from the Afrikaans word “klippie”, which is synonymous with the description of “small rock”. The instrument provides sufficient resolution and fidelity to investigate the relationship between ballast translation and rotation in three spatial dimensions for both laboratory and in-service track environments. Using multiple Kli-Pis
arranged in succession, the dynamic performance and characteristics (for both the time and frequency domain) of ballast in both laboratory and field environments can be remotely monitored in real-time. Statistical parameters and energy metrics are formulated to compare and quantify the measured laboratory and field characteristics of ballast.
Through this research, Kli-Pi has been developed to provide valuable information surrounding the rotations and deflections in three dimensions, dominant frequencies and harmonics of the track components, indirect observations of principal stress rotations (PSR) and the underlying probabilistic micromechanics and statistical nature of the mesoscale ballast dynamics. Contrary to traditional deterministic mechanics, the probabilistic nature of the material does not conform to uniform-strain assumptions. Probabilistic behaviour governs the particle deflections where instances of alternating positive and negative strain are observed in the vertical direction. For both the laboratory and field experiments investigated, the largest component of the energy was concentrated along the vertical direction, parallel to the direction of the load. The passage of the locomotives coincided with significant longitudinal and lateral forces from the tractive effort, the influence of which extended to the subballast interface. Kli-Pi provided the necessary sensitivity to observe changes in the skeletal structure or “fabric” of the ballast and the influence of impact loads. Finally, the kinetic energy of each Kli-Pi was quantified which relates statistical parameters such as standard deviation and skewness with the particle coordination number (CN) and relative degrees of confinement. Of all the statistics investigated to quantify the ballast dynamics, the mechanical work proved to be the most suitable descriptor, exemplifying the fundamental, probabilistic response of ballast subjected to dynamic loading conditions.Civil EngineeringMEngUnrestricte
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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