Eugenio Oñate

A plastic-damage model for concrete

In this paper a constitutive model based on an internal variable-formulation of plasticity theory for the non-linear analysis of concrete is presented. The model uses a new yield criterion which matches experimental data quite well and it accounts for both elastic and plastic stiffness degradations effects. Onset and amount of cracking can be studied by a simple postprocessing of the finite-element plasticity solution. The accuracy of the model is checked with some examples of application.

A FINITE POINT METHOD IN COMPUTATIONAL MECHANICS. APPLICATIONS TO CONVECTIVE TRANSPORT AND FLUID FLOW

The paper presents a fully meshless procedure fo solving partial differential equations. The approach termed generically the ‘finite point method’ is based on a weighted least square interpolation of point data and point collocation for evaluating the approximation integrals. Some examples showing the accuracy of the method for solution of adjoint and non-self adjoint equations typical of convective-diffusive transport and also to the analysis of compressible fluid mechanics problem are presented.

A stabilized finite point method for analysis of fluid mechanics problems

In this paper a meshless procedure termed ‘the finite point method’ for solving convection-diffusion and fluid flow type problems is presented. The method is based on the use of a weighted least-square interpolation procedure together with point collocation for evaluating the approximation integrals. Special emphasis is given to the stabilization of the convective terms and the Neumann boundary condition which has been found to be essential to obtain accurate results. Some examples of application to diffusive and convective transport and compressible flow problems using quadratic FP interpolations are presented.

Plate bending elements with discrete constraints: New triangular elements

Abstract In recent years a series of elements based on Reissner-Mindlin assumptions and using discrete (collocation type) constraints has been introduced. These elements have proved to be very effective, however their relation to straightforward mixed approximations has not been clear. In this paper this relationship is discussed and the reasons for their success explained. This allows new and effective triangular elements to be developed. The presentation shows the close relationships with the DKT (Discrete Kirchhoff Theory) element previously available only for thin plates and allows extension of their applications

The intrinsic time for the streamline upwind/Petrov-Galerkin formulation using quadratic elements

Abstract In this paper the functions of the Peclet number that appear in the intrinsic time of the streamline upwind/Petrov-Galerkin (SUPG) formulation are analyzed for quadratic elements. Some related issues such as the computation of the characteristic element length and the introduction of source terms in the one-dimensional model problem are also addressed.

Finite element nonlinear analysis of concrete structures using a “plastic-damage model”

Abstract In this paper a plastic damage model for nonlinear finite element analysis of concrete is presented. The model is based on standard plasticity theory for frictional materials. Details of the expressions of a new yield function proposed and of the evolution laws of the model parameters are given. The model allows to include elastic and plastic stiffness degradation effects. This is also discussed in the paper together with the problem of mesh objectivity, and the a posteriori determination of cracks. Finally, one example of application which shows the accuracy of the model is also given.

Polyhedrization of an arbitrary 3D point set

Given a 3D point set, the problem of defining the volume associated, dividing it into a set of regions (elements) and defining a boundary surface is tackled. Several physical problems need to define volume domains, boundary surfaces and approximating functions from a given point distribution. This is for instance the case of particle methods, in which all the information is the particle positions and there are not boundary surfaces definition. Until recently, all the FEM mesh generators were limited to the generation of simple elements as tetrahedral or hexahedral elements (or triangular and quadrangular in 2D problems). The reason of this limitation was the lack of any acceptable shape function to be used in other kind of geometrical elements. Nowadays, there are several acceptable shape functions for a very large class of polyhedra. These new shape functions, together with a generalization of the Delaunay tessellation presented in this paper, gives an optimal marriage and a powerful tool to solve a large variety of physical problems by numerical methods. The domain partition into polyhedra presented here is not a standard mesh generation. The problem here is: for a given node distribution to find a suitable boundary surface and a suitable mesh to be used in the solution of a physical problem by a numerical method. To include new nodes or change their positions is not allowed.

An anisotropic elastoplastic constitutive model for large strain analysis of fiber reinforced composite materials

In this work a generalized anisotropic elastoplastic constitutive model for the large strain analysis of fiber-reinforced composite materials in the frame of the mixing theory and the finite element method is presented. The isotropic equivalent formulation proposed assumes the existence of a fictitious isotropic space where a mapped fictitious problem is solved. Both real anisotropic and fictitious spaces are related by means of linear fourth-order transformation tensors that contain the complete information about the real anisotropic material. Details of the numerical implementation of the model into a non-linear or large strain finite element solution scheme are provided. Application examples showing the performance of the model for analysis of fiber reinforced composite materials are given.

VISCOUS DAMAGE MODEL FOR TIMOSHENKO BEAM STRUCTURES

Abstract A local damage constitutive model based on Kachanovs theory is used within a finite element frame and applied to the case of 2D and 3D Timoshenko beam elements. The model takes into account viscous effects, thus allowing damping to be considered in a rigorous way. A damage index based on potential energy criteria, useful in evaluating the behaviour of structures or of parts of structures, is proposed. The procedure is applied to estimate the damage produced by seismic actions in reinforced concrete building structures, whose response is computed by using a non-linear Newmark-type incremental time integration scheme. Three numerical examples are included; one of them compares results obtained by using the proposed model with results of a laboratory test.

A simple method for automatic update of finite element meshes

A simple method to automatically update the finite element mesh of the analysis domain is proposed. The method considers the mesh as a fictitious elastic body subjected to prescribed displacements at selected boundary points. The mechanical properties of each mesh element are appropriately selected in order to minimize the deformation and the distortion of the mesh elements. Different selection strategies have been used and compared in their application to simple examples. The method avoids the use of remeshing in the solution of shape optimization problems and reduces the number of remeshing steps in the solution of coupled fluid–structure interaction problems. Copyright