1,721,024 research outputs found
The role of soil constitutive modelling on the assessment of seismic performance of caisson foundations
No full textIn this paper, the influence of inelastic soil behaviour on the seismic performance of bridge piers supported by caisson foundations is assessed. The results of an extensive parametric study, performed assuming a linear elastic and an elastic-plastic soil behaviour, are compared, showing the strong influence of the inelastic soil response. The geometrical properties of caissons and piers are varied; the systems are subjected to seismic records capable of mobilising the shear strength of the soil. 3D dynamic analyses are performed in the time domain and in terms of effective stresses but assuming undrained conditions. The role of soil constitutive modelling is assessed by comparing the deck drift and the forces transmitted by the superstructure to the caissons, both computed under the assumption of linear elastic and elastic-plastic soil behaviour. The results clearly indicate for which systems the linear elastic assumption is satisfactory and when, conversely, soil non-linearities should be considered
Numerical back-analysis of dynamic centrifuge tests on the seismic behaviour of caisson foundations supporting bridge piers
No full textOver the last few years, an ever-increasing interest on a sort of a “Reversed” Capacity Design of geotechnical systems has been emerging, particularly when looking at the seismic design of bridge foundations, such as shallow, piled and caisson foundations. In this approach, soil irreversible behaviour is triggered on purpose during strong seismic events, so as to protect the superstructure. Although the capacity of soil-caisson systems is quite high if compared to shallow and piled foundations, limit conditions of these systems may be actually attained during destructive seismic events. The above-mentioned framework boosted the research on the dynamic response and interaction diagrams (i.e., failure envelopes) of rigid and massive caisson foundations [1][2]. Gaudio et al. [3] recently performed an experimental campaign via dynamic centrifuge tests, where a typical layout of a cylindrical caisson supporting a bridge pier was subjected to a series of ground motions. The caisson was embedded in a typical alluvial deposit, where the clay stratum was either soft and very soft. In this paper, the results of preliminary 3D Finite Element back-analyses reproducing the centrifuge test are presented and discussed, for the specific soft-clay case. The analysis first aimed at reproducing and then extending the experimental investigation, so as to both validate and better understand the phenomena observed in the centrifuge. It is shown that, even with a simple but still comprehensive calibration of handy soil constitutive models, the main features ruling the seismic performance of the systems at hand can be fairly captured
An uncoupled approach for estimating seismic-induced pore water pressures in liquefiable sandy soils
No full textProper evaluation of seismic-induced excess pore water pressures in saturated sandy soils is still an open issue, which can be tackled with fully coupled to uncoupled approaches. The former are more accurate but computationally onerous, while the latter require seismic demand and pore pressure build-up to be computed in two successive steps, typically employing simple constitutive assumptions. Starting from the work by Seed et al. (1975), this paper presents a novel uncoupled procedure to compute excess water pressures developing in a 1D soil column under partially drained conditions, when subjected to horizontal seismic excitations. Fundamental modifications are introduced to account for: non-uniform distribution of equivalent loading cycles; soil stiffness degradation; and modification of the frequency content of ground motion due to pore pressure build-up. The approach was implemented in Matlab via the Finite Difference Method and validated against both fullycoupled Finite Element analyses and one centrifuge test. An extensive parametric study was also performed for a two-layer soil column, by varying the thickness and hydraulic conductivity of the shallow layer, as well as the seismic input. The good agreement with both numerical and experimental data demonstrates that key features of liquefaction are well-captured by the proposed uncoupled approach
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
A simplified procedure for the evaluation of the seismic performance of bridge piers on caisson foundations
Full text linkIn this paper, a simplified procedure for the evaluation of the seismic performance of bridge piers founded on caissons subjected to strong ground motions is outlined. To this end, the up-per-bound semi-empirical relationships proposed in [1] are considered for the estimation of the seismic performance, expressed in terms of the maximum and permanent values of the deck drift ratio attained during and at the end of the seismic event. These drifts were related to the period ratio Teq/T0 between the fundamental periods of the deck-pier-caisson-soil sys-tem and of the soil column in free-field conditions. The deck drift and the period ratios were extracted from the results of an extensive parametric study, where 14 different systems were subjected to 6 real high-intensity seismic records. In the parametric study, 3D dynamic anal-yses were performed with the Finite Element Method in the time domain, in terms of effective stresses but assuming undrained conditions and adopting an elastic-plastic constitutive model to reproduce the irreversible soil behaviour under cyclic loading. As 3D dynamic numerical analyses are not expected to become an every-day design tool, the period ratios Teq/T0 are evaluated through empirical and analytical relationships available in the literature as well and then compared with the ratios obtained from the parametric study, to assess the possibil-ity of using simplified relationships while still getting a reliable estimate of the deck drift ra-tio. It is shown that these relationships can be profitably adopted provided that a fair estimate of the equivalent shear wave velocity, depending on the intensity of the seismic inputs, is used
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
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe 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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