(2004) suggested that axially loaded piles may collapse as a result of buckling instability if the soil bracing effect is removed due to liquefaction. When axially-loaded piles lose the lateral support due to soil liquefaction, they behave like unsupported, axial and lateral load bearing structural elements. INTRODUCTION Piles are slender structural elements with lateral support offered from the surrounding soil. Pile, Foundation, Liquefaction, Buckling, Eigenvalue, Fixity.ġ. The FE, elastic-continuum model has then been used to analyse the buckling of pile foundations in liquefied soils for the parameters: depth of liquefaction, stiffness of the liquefied soil, and exposed length of the piles. Results from the FE, elastic-continuum model, for a pile embedded in soil, have been compared with documented equivalent Winkler foundation analytical studies, and experimental results. The program ABAQUS has been used to build and analyse a finite-element (FE), perfectly elastic, continuum, soil-pile model. This paper investigates the stability of pile foundations in liquefied soils via a more accurate three dimensional (continuum) model. Most research in the area of pile stability is based on the use of Winkler foundation (p-y method), which models the lateral restraining effect of the soil on the pile as a set of discrete one-dimensional springs distributed along the length of the pile. The method would be applicable to simple structures such as bridges or jetties, which provide no moment or lateral restraint at the top end of the pile. This paper presents a simple method, based on an elastic analysis, which may be used to estimate the unsupported buckling length of piles in liquefied soil. Buckling is a non-ductile method of failure which results in a rapid collapse and it should be avoided in the design process. This makes it vulnerable to buckling instability. Lubkowski4 1īuildings’ Structural Engineer, Arup, UK University Lecturer in Dynamics ,University of Bristol, UK 3 University lecturer in Engineering Science, University of Oxford, UK 4 Associate Director, Arup, UK 4 Email:, , 2ĪBSTRACT : A pile becomes laterally unsupported when the soil liquefies during strong earthquakes. All rights reserved.The 14 World Conference on Earthquake Engineering October 12-17, 2008, Beijing, ChinaįIXITY OF PILE FOUNDATIONS IN SEISMICALLY LIQUEFIED SOILS FOR BUCKLING CALCULATIONS – AN EIGENVALUE ANALYSIS 1Ī.
HGO MODEL ABAQUS 6.13 FULL
Significantly higher stress triaxiality and arterial compliance are computed when the full anisotropic invariants are used (MA model) instead of the isochoric form (HGO-C model).Īnisotropic Artery Finite element Hyperelastic Incompressibility Stent.Ĭopyright © 2014 Elsevier Ltd. To look at more practical applications, we developed a finite element user-defined material subroutine for the simulation of stent deployment in a slightly compressible artery. It also computes the correct anisotropic stress state for pure shear and uniaxial deformations. The MA model correctly predicts an anisotropic response to hydrostatic tensile loading, whereby a sphere deforms into an ellipsoid. In order to correctly model compressible anisotropic behaviour we present a modified anisotropic (MA) model, whereby the full anisotropic invariants are used, so that a volumetric anisotropic contribution is represented. Here, by using three simple deformations (pure dilatation, pure shear and uniaxial stretch), we demonstrate that the compressible HGO-C formulation does not correctly model compressible anisotropic material behaviour, because the anisotropic component of the model is insensitive to volumetric deformation due to the use of isochoric anisotropic invariants. A compressible form (HGO-C model) is widely used in finite element simulations whereby the isotropic part of Ψ is decoupled into volumetric and isochoric parts and the anisotropic part of Ψ is expressed in terms of isochoric invariants. Such materials can be regarded as incompressible, and when the incompressibility condition is adopted the strain energy Ψ of the HGO model is a function of one isotropic and two anisotropic deformation invariants. The Holzapfel-Gasser-Ogden (HGO) model for anisotropic hyperelastic behaviour of collagen fibre reinforced materials was initially developed to describe the elastic properties of arterial tissue, but is now used extensively for modelling a variety of soft biological tissues.
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