This paper extends to three dimensions (3D) the computational technique developed by the authors in 2D for predicting the onset and evolution of fracture in a finite element mesh in a simple manner based on combining the finite element method (FEM) and the discrete element method (DEM) approach [23]. Once a crack is detected at an element edge, discrete elements are generated at the adjacent element vertexes and a simple DEM mechanism is considered in order to follow the evolution of the crack. The combination of the DEM with simple 4noded linear tetrahedron elements correctly captures the onset of fracture and its evolution, as shown in several 3D examples of application.

No abstract

The main purpose of this paper is to develop a reliable method based on a three-dimensional (3D) finiteelement (FE) model to simulate the constitutive behaviour of reinforced concrete structures strengthened with post-tensioned tendons taking into account the reduction of the pre-stressing stress due to the steel relaxation. The pre-tensioned concrete is modelled as a composite material whose behaviour is described with the serial-parallel rule of mixtures (S/P RoM) [1-3] whereas the stress relaxation of the steel is simulated using a viscoelastic model called Generalized Maxwell. A 3D FE model was used, where the nonlinear material behaviour and geometrical analysis based on incremental-iterative load methods were adopted. Validation by comparison with the analytic solution will be done for the case of a concrete beam with a parabolic pre-tensioned steel tendon embedded and some viscoelastic cases are performed in order to perceive the behaviour of the Generalized Maxwell model. Several examples are shown where the capabilities of the method on large scale structures are exhibited.

This paper presents an enhanced coupled approach between the Finite Element Method (FEM) and the Discrete Element Method (DEM) in which an adaptative remeshing technique has been implemented. The remeshing technique is based on the computation of the Hessian of a selected nodal variable, i.e. the mesh is refined where the curvature of the variable field is greater. Once the Hessian is known, a metric tensor is defined node-wise that serves as input data for the remesher (MmgTools) that creates a new mesh. After remeshing, the mapping of the internal variables and the nodal values is performed and a regeneration of the discrete elements on the crack faces of the new mesh is carried out. Several examples of fracturing problems using the enhanced FEM-DEM formulation are presented. Accurate results in comparison with analytical and experimental solutions are obtained.