1,720,999 research outputs found
Testing Aggregate Backfill for Corrosion Potential
Get PDFThe Kansas Department of Transportation (KDOT) has designed and constructed numerous mechanically stabilized earth (MSE) walls to support new and expanded highway projects throughout Kansas. MSE walls often contain galvanized steel strips as mechanical reinforcement within layers of specified backfill material. Inclusion of these strips creates a stronger composite material connected to a visually appealing wall facing, however galvanized steel reinforcement is potentially vulnerable to corrosion. Corrosivity of MSE backfill is typically characterized using electrical resistivity among other properties. KDOT currently uses the American Association of State Highway and Transportation Officials (AASHTO) standard T 288 to calculate the resistivity of MSE backfill. There is concern that this method may not reflect field conditions well, and thus may mischaracterize the corrosivity of backfill. AASHTO T 288 tests were conducted as a part of this research, and the condition of these samples during testing was not consistent with expected field conditions. A new procedure has been proposed to ASTM that appears to more accurately simulate field conditions behind MSE walls. This ASTM C XXX-XX (the New ASTM) has been extensively tested and compared with AASHTO T 288 in this experimental study. The New ASTM simulated expected field conditions more accurately than the AASHTO test. Results also appear to indicate the need for a larger resistivity box to accurately characterize the corrosivity of larger aggregates. Preliminary recommendations for box geometry are 8:1 minimum electrode spacing to maximum particle size and 3:1 minimum height to maximum particle size. It was also observed that increasing the number of soak/drain cycles of the material resulted in a substantial increase in resistivity values that plateaued at a higher value than observed for both the AASHTO and proposed ASTM methods
Effect of Column Stiffness on Consolidation Behavior of Stone Column-Treated Clay
Get PDFStone columns have been proved an effective ground improvement technique. The increase in land prices and the existence of soft clay deposits in many areas around the world has encouraged the use and development of this technique. Stone columns can be used to accelerate the consolidation of soft clay deposits through two mechanisms. First, the stone columns act as vertical drains that provide additional drainage path for excess pore water pressure to dissipate. Second, they reduce the excess pore water pressure by transferring more load from the soil to the columns because they are stiffer than the surrounding soil. Stone columns may not work well in very soft soil due to bulging of the columns. Woven geotextile has been used to minimize bulging of the columns and improve their performance (capacity and stiffness). For the geotextile encased stone columns, geotextile filtration adds another benefit by minimizing fine particles migrating from the surrounding soil into the stone columns and maintaining their high permeability in a long term. The increased stiffness of the stone columns by the geotextile is expected to have an effect on the consolidation rate. However, this effect has not been well investigated. This study investigated the effect of column stiffness on the consolidation behavior and the stress transfer mechanism of the stone column-reinforced foundation through several small-scale model tests. Both ordinary and geotextile encased stone columns were utilized. For comparison purposes, a special PVD “column” was formed, which had nearly zero stiffness. In each test, a soil bed was first formed from a slurry by preloading in a rigid steel chamber with a dimension of 280 mm in diameter and 450 mm in height. A model stone column of 100 mm in diameter was installed in the center of the soil bed to the bottom of the steel chamber. Piezometers were placed inside the chamber at different depths and distances to the center to measure the generation and dissipation of excess pore water pressure. The pressure was applied in increments on a steel plate seated on the soil. After the application of each pressure increment, the pressure was maintained until the plate displacement was smaller than 1 mm/day. The vertical stress transfer between the soft soil and the column was monitored by earth pressure cells on the soil and the column. The test results show that the ordinary stone columns effectively reduced the consolidation time by 25%, as compared with the PVD “column”, while the encased stone columns further reduced the time by 40%. The ordinary stone columns also reduced the settlement by 36% as compared with the PVD “column” while the encased columns further reduced the settlement by 56%. The test results show that the stone columns with and without geotextile encasement carried more load than the surrounding soil. The steady stress concentration ratio, defined as the stress on the column to that on the soil, was found in the range of 4 to 6 for ordinary stone columns while it ranged from 4 to 11 for the encased stone columns. The modulus improvement factor, defined as the modulus of the PVD “column” treated foundation to that of a stone column treated foundation, was found to be 1.7 and 2.4 for the ordinary and encased stone columns, respectively. Finally, the theoretical solutions developed by Han and Ye (2001, 2002) were used to compare with the test results. The comparisons show good agreement between the theoretical solutions and the test results
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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
Pullout Resistance of MSE Wall Steel Strip Reinforcement in Uniform Aggregate
Get PDFA wide range of reinforcement-backfill combinations have been used in mechanically stabilized earth (MSE) walls. Steel strips are one type of reinforcement used to stabilize aggregate backfill through anchorage. In the current MSE wall design, pullout capacity of steel strips is evaluated to ensure internal stability of the reinforced mass. The pullout resistance of reinforcement is expressed in terms of a pullout resistance factor that measures the reinforcement-backfill interaction. This pullout resistance factor is commonly determined by performing pullout tests. AASHTO (2012) LRFD Bridge Design and Specifications provides default values of the pullout resistance factor, F*, for strip reinforcement embedded in backfill material with a uniformity coefficient of Cu ≥ 4, where the uniformity coefficient is defined as the ratio of the particle size at 60% finer to that at 10% finer. However, for backfill with a uniformity coefficient, Cu<4, AASHTO (2012) requires project-specific pullout tests. This AASHTO requirement has disqualified a large amount of aggregates produced in Kansas quarries or made them difficult and/or costly to be used in MSE wall construction. To address this problem, an experimental study was undertaken in the Geotechnical Engineering Laboratory at the University of Kansas to examine the effect of aggregate uniformity on pullout resistance of steel strips when the uniformity coefficient of aggregate, Cu<4. Twenty-two pullout tests were carried out on ribbed steel strip reinforcements embedded in six aggregate backfills of uniformity coefficients ranging from 1.4 to 14. The pullout resistance of each reinforcement-backfill combination was investigated under normal stresses of 25, 41 and 69 kPa to simulate reinforcements placed at different depths of fill. Additionally, aggregate backfills with Cu=1.4 and 14 were tested under normal stresses of 103 and 138 kPa to further evaluate the pullout resistance at higher depths. Each test sample was prepared in a consistent way to minimize variations. One of the important influence factor was degree of compaction. The test results demonstrated that the overall trend for all types of aggregates was similar. The uniform aggregates generally behaved in the same way as the well-graded aggregates in terms of pullout resistance. The effect of aggregate uniformity was more obvious in the tests under a lower normal stress than under a higher normal stress. When the normal stress was at 69 kPa, there was no obvious effect of aggregate uniformity. Furthermore, the pullout resistance factors obtained from this study were compared with the default F* values for ribbed strip reinforcement provided by AASHTO (2012). The comparison shows that the pullout resistance factor for ribbed steel strips decreased with depth in the same way as suggested by AASHTO (2012). However, the F* values recommended by AASHTO (2012) are conservative as compared with the test results when aggregate backfills with the uniformity coefficients ranging from 1.4 to 14 were used. In other words, the F* values recommended by AASHTO (2012) can be used to design MSE walls with ribbed steel strips in aggregate backfills of the uniformity coefficient as low as 1.4 provided the backfill meets the AASHTO (2010) requirements
Thermodynamic Consistency of the currently used Beam Mathematical Models and Thermodynamically Consistent New Formulations for Bending of Thermoelastic, and Thermoviscoelastic Beams
Get PDFIn order to enhance currently used beam mathematical models in R^2 and R^3 to include mechanisms of dissipation and memory, it is necessary to establish if the mathematical models for these theories can be derived using the conservation and the balance laws of continuum mechanics in conjunction with the corresponding kinematic assumptions. This is referred to as thermodynamic consistency of the beam mathematical models. Thermodynamic consistency of the currently used beam models will permit use of entropy inequality to establish constitutive theories in the presence of dissipation and memory mechanism for the currently used beam mathematical models. This is the main motivation for the work presented in this dissertation. The currently used beam mathematical models for homogeneous, isotropic matter and reversible deformation physics are derived based on kinematic assumptions related to the axial and transverse displacement fields. These are then used to derive strain measures followed by constitutive relations. For linear beam theories, strain measures are linear functions of displacement gradients and stresses are linear functions of strain measures. Using these stress and strain measures, energy functional is constructed over the volume of the beam consisting of kinetic energy, strain energy and potential energy of loads. The Euler's equation(s) extracted from the first variation of this energy functional set to zero yield the differential equations describing the evolution of the deforming beam. Alternatively, principle of virtual work can also be used to derive mathematical models for beams. For linear elastic behavior with small deformation and small strain these two approaches yield same mathematical models. The energy methods or the principle of virtual work cannot be used for irreversible process, thus precluding their use in the presence of dissipation and memory mechanisms. In this dissertation we examine whether the currently used beam mathematical models for reversible deformation physics and with the corresponding kinematic assumption (i) can be derived using the conservation and balance laws of classical continuum mechanics or (ii) are the conservation and balance laws of non-classical continuum mechanics necessary in their derivation. In order to ensure that the mathematical models for various beam theories result in deformation that is in thermodynamic equilibrium we must establish the consistency of the beam theories with regard to the conservation and the balance laws of continuum mechanics, classical or non-classical in conjunction with their corresponding kinematic assumptions. Currently used Euler-Bernoulli and Timoshenko beam mathematical models that are representative of most beam mathematical models are investigated. This is followed by details of general and higher order thermodynamically consistent beam mathematical models that is free of kinematic assumptions and other approximations and remains valid for slender as well as deep beams. Model problem studies are presented for slender as well as deep beams. The new formulation presented here ensures thermodynamic equilibrium as it is derived using the conservation and the balance laws of continuum mechanics and remains valid for slender as well as non-slender beams. The new formulation presented for thermoelastic reversible mechanical deformation is extended for thermoviscoelastic beams with dissipation and for thermoviscoelastic beams with dissipation and memory. In each case model problem studies are presented using currently used mathematical models (when possible) and the results are compared with those obtained using the new thermodynamically consistent formulation presented here
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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