1,720,978 research outputs found
Kinematic bending of fixed-head piles in nonhomogeneous soil
No full textAbstractKinematic bending of elastic single fixed-head piles in continuously inhomogeneous soil is explored in both static and dynamic regime. A generalized parabolic function is employed to describe the variable shear modulus in the inhomogeneous stratum, which can simulate both cohesive and cohesionless soil deposits. The problem is treated numerically by means of rigorous elastodynamic finite-element analyses and simplified beam-on-dynamic-Winkler-foundation (BDWF) formulations. A novel expression is proposed for the active length of a pile in inhomogeneous soil, by means of kinematic interaction considerations. This allows an alternative interpretation of kinematic soil-pile interaction along an effective depth, contrary to existing definitions in which soil response is evaluated at a specific location. Following this interpretation, a design formula for kinematic pile-head moments is derived for both static and dynamic loading. A new dimensionless parameter is identified to govern dynamic pile bending, which allows a straightforward assessment of frequency effects in pile design
Reduction of Seismic Loading on Structures Induced by Piles in Inhomogeneous Soil
Full text linkThe kinematic response of flexible piles in inhomogeneous soil is explored under
harmonic and seismic excitation. The system under investigation consists of a long fixed-head
pile embedded in viscoelastic soil with stiffness varying continuously with depth. A generalized
power-law function is employed to describe the variable soil stiffness. The problem is
treated numerically by means of a Beam-on-Dynamic-Winkler-Foundation (BDWF) model
based on a layer transfer-matrix (Haskel-Thompson) formulation. This study aims at: (a) investigating
numerical and modeling aspects related to Winkler analyses of soil-pile kinematic
interaction in a non-homogeneous soil; (b) exploring soil-pile kinematic interaction as affected
by varying subsoil conditions under harmonic oscillations; (c) providing a novel closedform
expression for the kinematic interaction factor of pile-head over free-field response as a
function of a single dimensionless frequency controlling the physical phenomenon and (d)
elucidating the beneficial role of piles in the reduction of seismic loading imposed on pilesupported
structures in terms of spectral acceleration for different pile-soil configurations
and earthquake motions. Results show that: (a) large-diameter piles in soils with very low
stiffness at shallow depths may substantially reduce the seismic acceleration imposed on
structures and (b) the role of pile diameter becomes less important for strongly inhomogeneous
soils. The latter indicates that even small-diameter piles may induce substantial filtering
of ground motion if embedded in soft clays, which may be of importance in pile design practice
Evidenza sperimentale dell’interazione dinamica terreno-pali-struttura in argilla soffice da prove in centrifuga.
No full textKinematic Soil-Pile Interaction under Earthquake-Induced Nonlinear Soil and Pile Behavior: An Equivalent-Linear Approach
Full text linkThe kinematic bending and filtering potential of a fixed-head pile are explored when large shear strains are generated in the surrounding soil during the passage of seismic waves. The problem is treated numerically by employing a freely available 1D code to derive soil response at free-field conditions and an advanced 3D finite-difference (FD) model of the soil-pile system. Three idealized soil profiles with varying stiffness and strength and a real layered site are considered under earthquake excitations of increasing intensity, allowing investigation of the pile's non-linear kinematic response under shear strains exceeding the threshold of an equivalent-linear approximation. Simple analytical solutions are revisited in the context of soil response close to failure, by means of the FD solution, and an equivalent linear approach is proposed for assessing kinematic pile-head bending and filtering action in the presence of large earthquake-induced shear strains in the soil and non-linear pile behavior. A practice-oriented procedure requiring only a pertinent 1D soil response analysis is proposed to address kinematic effects in seismic design of piles
The beneficial role of fixed-head piles on the seismic loading of structures
No full textWe examine the kinematic response of fixed-head vertical floating piles embedded in continuously nonhomogeneous soils and subjected to upward propagating seismic waves. The problem is explored numerically by means of a rigorous finite element (FE) model of the soil-pile system to quantify the kinematically induced reduction of the horizontal free-field spectral acceleration. Soil stiffness varies continuously with depth according to a generalized power law function. We show that kinematic pile response in the harmonic regime is controlled by a unique dimensionless frequency parameter involving the active pile length in a generalized nonhomogeneous soil. A new, simplified expression for the horizontal kinematic interaction factor Iu is proposed for practical time-domain applications while a novel physical interpretation of the filtering action of piles is reported by introducing the role of pile stiffness in averaging soil motion over an effective pile length. Following a parametric study under transient motion, we propose a set of novel, ready-to-use formulae for a rapid assessment of the pile-induced filtering action. An application of the proposed formulae to clayey soils is finally presented, leading to useful indications for the selection of the pile diameter associated with the maximum filtering potential
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
Seismic Response of Inhomogeneous Soil Deposits with Exponentially Varying Stiffness
No full textThe response of an inhomogeneous soil layer with exponentially varying stiffness with depth is explored using one-dimensional viscoelastic wave propagation theory. The governing equation is treated analytically, leading to an exact harmonic solution of the Bessel type. Both positive and negative velocity gradients are examined using a pertinent dimensionless parameter. It is shown that (1) for positive stiffness gradients, strains attenuate with depth faster than displacements that, in turn, attenuate faster than stresses; and (2) close to the soil surface, curvatures are controlled by acceleration, whereas they are controlled by strain at depth. The fundamental natural frequency of the layer compares well against approximations on the basis of the Rayleigh quotient. Novel asymptotic and ad hoc approximate solutions for the base-to-surface transfer function are proposed, providing good alternatives to the complex exact solution at both high and low frequencies. New expressions are derived relating (1) shear strain and peak particle velocity; and (2) curvature and peak ground acceleration close to the soil surface. A full-domain approximation is provided, allowing the practical implementation of the specific velocity model. Numerical examples are presented
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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