1,721,019 research outputs found
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
Analysis of shaft resistance of jacked and drilled-displacement piles
No full textSignificant developments in piling technology over the last few decades have yielded a variety of new pile types. Jacked and Drilled-Displacement (DD) piles, for example, are two emerging pile types that are becoming increasingly popular in geotechnical engineering practice. Jacking of steel or precast concrete piles into the ground is an effective and environmentally friendly pile installation technique (produces minimal noise, vibration and air pollution). DD piles, which are installed using a drilling tool consisting of a partial-flight auger and a displacement body, are a new generation of rotary displacement piles. Different types of DD piles are available in practice; each type is classified according to the design of the drilling tool and associated installation method. Installation of a pile often involves complex loading modes that cause substantial changes in the state of the soil surrounding the pile. As a result of these changes, the response of piles to structural loads varies greatly depending on the installation method used. For reliable estimation of pile capacity, design methods should account for the effect of the installation technique. Empirical or semi-empirical equations, based on results of load tests performed on driven piles (i.e., piles installed using hammers or vibrators), are often used to calculate the capacity of jacked piles. However, the mechanics involved in pile driving (a dynamic process) differ from those prevalent in pile jacking (a quasi-static process). Similarly, the currently available design methods for DD piles rely exclusively on empirical relations developed based on the results of load tests performed on particular types of DD piles installed at specific sites. No theoretical research has been performed to assess the effect of the installation method on the shaft resistance of jacked and DD piles. In order to develop design equations for the calculation of the shaft resistance of these piles, we performed FE analyses using advanced constitutive models for sand and clay. The plasticity-based constitutive models capture key features of soil behavior during pile installation and loading. The proposed design equations involve installation parameters (e.g., number of jacking strokes for jacked piles, and rate of drilling for DD piles), in situ soil state and properties (e.g., relative density and confinement for sand and undrained shear strength for clay), and some other key soil characteristics (e.g., initial fabric anisotropy for sand, and residual shear strength for clay). Additionally, setup factors are proposed that can be used to estimate the gain in shaft resistance as a function of time after installation of jacked piles in clay. Good agreement was obtained between the shaft resistance values calculated with the proposed equations and the data available in the literature
Investigation of Monotonic and Cyclic Loading of Piles in Sand Using a DIC Calibration Chamber
No full textUnderstanding the response of piles subjected to cyclic loads is critical for piles subjected to extreme loading conditions, particularly in the offshore environment in which platforms and wind farms operate. Not only there is no specific understanding of quantitative aspects of the impact of cyclic loading on pile resistance, but also the mechanisms governing the cyclic and post-cyclic response of piles in silica sands are not well understood. The mechanisms governing pile resistance mobilization under monotonic (tensile and compressive) or cyclic axial loading were investigated by performing instrumented model piles tests in a novel half-cylindrical calibration chamber with three viewing windows that allow the capturing of digital images of the sand domain and the instrumented model pile during installation and testing.A set of tensile-compressive and compressive-tensile load tests were performed to study the effect of loading direction on the shaft resistance of model displacement and non-displacement piles. Measurements of displacements and deformations in the sand domain were obtained through the digital image correlation (DIC) technique. The tensile-to-compressive shaft resistance ratios were found to be a function of the loading history (installation method), loading sequence, and pile surface roughness. The results show that the tensile-to-compressive shaft resistance ratios are always less than one for jacked piles and nearly one for fresh preinstalled piles. The results from DIC analyses revealed that, when the loading direction is reversed, the soil elements near the pile shaft contract, and the direction of the principal strains rotate by about 90 degrees.A series of model pile experiments that included installation, monotonic and cyclic load tests were performed to study the effect of cyclic loading on the limit unit shaft resistance and limit and ultimate unit base resistance of displacement piles. The impact of (1) cyclic displacement half amplitude, (2) number of displacement cycles, (3) relative density, and (4) initial stress state on the pile resistance was assessed based on the pile load measurements obtained before and after cycling and on the displacement and strain fields from the DIC analysis. A minimal effect on the limit unit shaft resistance was observed after cycling in tests performed with small cyclic displacement half amplitudes (= 0.25 mm), regardless of the number of cycles (up to 2,000 cycles). For 100 cycles or more applied with cyclic displacement half amplitudes greater 0.7 mm, the limit unit shaft resistance after cyclic loading was found to be always smaller than the limit unit shaft resistance before cyclic loading. It was observed that the degradation of the limit unit shaft resistance after cycling increases with increasing initial vertical stress and with decreasing relative density. From the DIC analysis, it was found that the decrease in the limit unit shaft resistance after cyclic loading is linked to the radial contraction and the development of cyclic and permanent shear strains in soil elements near the pile shaft during cyclic loading. Finally, the results show that the ultimate unit base resistance can drop significantly after cycling. The magnitude of the drop in the ultimate unit base resistance depends on both the magnitude of the cyclic displacement and the number of cycles. This experimental program\u27s results provide a framework to improve the prediction of the capacity of piles subjected to cyclic loading
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
Study of the loading of piles using a semi-analytical method and the digital image correlation technique
Full text linkThe response of single piles and pile groups to axial and lateral loading and the displacements induced in the soil by it are studied in this work using theoretical and experimental approaches. The theoretical solution for the loading of piles is based on idealized displacement forms, energy principles and calculus of variations. The idealized displacement field is expressed in terms of a group of unknown functions that determine both the vertical profile of the displacement along the axis of the pile, which are obtained using the eigenvalue/eigenvector method, and another that determines the displacement within the soil domain, which are obtained numerically using the finite difference method. The piles can have any cross-sectional shape, and the soil profiles can comprise as many layers as needed. The pile and soil materials are assumed linear elastic. Analysis results are in a good agreement with results from the finite element method (FEM), with the advantage that the results are obtained at a lower computational cost. The experimental method used to study the displacement field in soil is the Digital Image Correlation (DIC) technique, used on images consists resulting from axial and lateral load tests on model piles installed in a calibration chamber. The calibration chamber is a half-section cylinder with transparent observation windows on its flat face. The soil and piles are photographed during the load tests and the response of soil is studied by analyzing the acquired images using the DIC technique. The information is combined with data from instrumentation of the piles and the load and deflection at the pile head to provide comprehensive data and insights into the response of the pile-soil system to loading
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
Use of tire shred-sand mixtures as backfill material for mechanically stabilized earth retaining walls
No full textEnormous quantities of waste tires are generated annually in all countries around the world. Efforts have been made to find applications for scrap tires in various industries. As a result, over the last few years there has been increased use of scrap tires in a variety of applications. One of the applications of scrap tires in civil engineering is in their use as a lightweight backfill material for mechanically stabilized earth (MSE) walls, where the shredded tires are mixed with sand. This has been shown to have several advantages, including lower vertical stress on weak foundation soils, lower horizontal pressures on the wall and good drainage properties. For tire shred-sand mixtures to be used as backfill material for MSE walls, their geotechnical properties need to be estimated. The pullout resistance of reinforcements embedded in tire shred-sand mixtures and the shear strength characteristics of the mixtures need to be determined. Conventional testing equipment proved to be unsuitable due to their small sizes relative to the size of the tire shreds. In this study, large-scale laboratory pullout tests were performed on reinforcement ladders embedded in mixtures prepared with tire shreds (size: 50-100 mm in length) and Ottawa sand. The pullout tests were performed at various mixing ratios (0:100, 20:80, 25:75, 35:75 and 45:55 by weight of tire shreds to sand) and confining pressures (40, 65 and 90 kPa). Large-scale direct shear tests were performed on tire shred-sand mixtures at mixing ratios of 20:80 and 35:65 by weight of tire shreds to sand. The results from the pullout tests showed that the pullout capacity of reinforcement ladders was higher in tire shred-sand mixtures than in pure sand. This can be attributed to the interlocking of tire shreds in the grids of the reinforcement ladder, thus providing higher passive resistance against pullout compared to that of pure sand. The pullout capacity increased with increases in the confining pressure at all mixing ratios. At a given confining pressure, increases in the tire shred content in the mixture typically resulted in higher pullout resistance. According to the results from the large-scale direct shear tests, critical-state friction angles of 30.1° and 32.0° and peak friction angles of 31.0° and 32° were obtained for tire shred-sand mixtures prepared at mixing ratios equal to 20:80 and 35:65 by weight of tire shreds to sand, respectively. When the results of the large-scale direct shear tests were plotted with a nonzero cohesive intercept, c-phi fitting parameters of 14.5 kPa and 27.1° and 10.3 kPa and 29.6° were obtained for tire shred-sand mixtures prepared at mixing ratios of 20:80 and 35:65 by weight of tire shreds to sand, respectively
Investigation of the response of pile groups subjected to combined loads
No full textVery limited experimental test data are available on the response of pile groups under the combined action of vertical and lateral loads. In practice, the loads applied on piles are often a combination of both vertical and lateral loads. In addition, piles are often arranged in groups, and the behavior of a pile group may differ substantially from that of a single pile. In this research, tests were performed on model pile groups subjected to both axial and lateral loads in order to evaluate the effects of pile-pile interaction in pile groups and to study the influence of axial loads on the lateral load response of pile groups in sands. The model pile groups tested consisted of 2×2, 1×2, and 1×3 piles. The model piles were driven into sand samples prepared at different densities using a large pluviator. The piles were then connected by a solid steel pile cap placed above ground level. The axial load (base and shaft) for a pile cap displacement of 10% of the pile diameter was first obtained from axial load tests. For all the model pile groups tested in dense sand, the group efficiency was a little less than unity, while in the case of the pile groups tested in medium dense and loose sand values of group efficiency higher than one were measured. The results of the lateral pile load tests were presented in terms of the lateral load-pile head displacement response of the model pile groups, the load experienced by the individual piles in the groups, and the bending moment profiles of the individual piles. The lateral load carried by each pile was obtained from strain gauges that were attached to the shaft of the piles 10cm below their head. The results showed that the leading piles experienced larger loads and bending moments than those experienced by the trailing piles due to the more intense pile-pile interaction. The combined load tests were performed for axial loads of 0% (pure lateral load), 25%, 50%, and 75% of the axial loads of the pile groups corresponding to a settlement of 10 % of the model pile diameter. The results of the combined load tests demonstrated that the bending moments and lateral deflections of the pile head increases substantially in the presence of axial loads with antifriction devices which provide minimal restraint to the lateral movement of the test piles
Dynamic analysis of dynamic cone penetration test for subgrade compaction assessment
Full text linkIn practice, soil compaction quality assessment relies on the determination of the in-place compacted dry unit weight, which is then compared with the maximum dry unit weight obtained from a laboratory compaction test. Most DOTs typically require that the in-place dry unit weight for compacted soil be over 95% of the laboratory maximum dry unit weight obtained from Standard Proctor compaction test results. Nuclear gauges may be used to determine the in-place dry unit weight, however, they are potentially hazardous and require safety precautions. Other tests, such as the Dynamic Cone Penetration Test (DCPT), can be used for soil compaction quality assessment. The main objectives of this research were to develop criteria for soil compaction quality assessment for different soils based on DCPT results. A number of DCPTs were performed on Indiana road sites, in a test pit, and in the soil test chamber at Purdue University. Since soil compaction varies spatially, a statistical approach was applied to the test measurements in the development of the criteria for soil compaction quality control. Based on the results of DCP tests performed on INDOT road sites and the requirement that the in-place dry unit weight of the fill material be over 95% of the laboratory maximum dry unit weight obtained from standard Proctor compaction tests, correlations that can be used to obtain the minimum required DCP blow count (NDCP)req were proposed for soils belonging to three groups of the AASHTO (American Association of State Highway and Transportation Officials) soil classification system. A series of tests were performed in the laboratory to determine the matric suction in compacted silty clays for different compaction conditions. Based on the results of the tests performed in this research and those available in the literature, a method was proposed that can be used to estimate the shear strength and small-strain shear modulus of compacted silty clays. A dynamic analysis, accounting for the increase in shear strength and stiffness due to matric suction in compacted soils, was used to predict DCPT results, which were then compared with DCP blow counts measured in the field. The results of this study are very useful for facilitating the use of DCPT as a tool for compaction quality control
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