Abstract

It is well known that in civil engineering structures are designed so that they remain, whenever possible, in an elastic regime and with their mechanical properties intact. The truth is that in reality there are uncertainties either in the execution of the work (geometric errors or material quality) or during its subsequent use (loads not contemplated or its value has been estimated incorrectly) that can lead to the collapse of the structure. This is why the study of the failure of structures is inherently interesting and, once is known, its design can be improved to be the less catastrophic as possible or to dissipate the maximum energy before collapsing. Another area of application of fracture mechanics is that of processes of which interest lies in the breakage or cracking of a medium. Within the mining engineering we can enumerate several processes of this nature, namely: hydraulic fracture processes or fracking, blasting for tunnels, explosion of slopes in open pit mines, among others. Equally relevant is the analysis of structural failures due to natural disasters, such as large avenues or even tsunamis impacting protection structures such as walls or dikes. In this work numerous implementations and studies have been made in relation to the mentioned processes. That said, the objective of this work is to develop an advanced numerical method capable of simulating multi-fracture processes in materials and structures. The general approach of the proposed method can be seen in various publications made by the author and directors of this work. This methodology is meant to cover the maximum spectrum of engineering applications possible. For this purpose, a coupled formulation of the Finite Element Method (FEM) and the Discrete Element Method (DEM) is used, which employs an isotropic damage constitutive model to simulate the initial degradation of the material and, once the strength of the material has been completely exhausted, those Finite Element (FE) are removed from the FEM mesh and a set of Discrete Element (DE) are generated at its nodes. In addition to ensure the conservation of the mass of the system, these DE prevent the indentation between the fissure planes thanks to the frictional repulsive forces calculated by the DEM, if any. Additionally, in this work it has been studied how the proposed coupled method named FEM-DEM together with the smoothing of stresses based on the super-convergent patch is able to obtain reasonably meshindependent results but, as one can imagine, the crack width is directly related to the size of the elements that have been removed. This favours the inclusion of an adaptive remeshing technique that will refine the mesh where it is required (according to the Hessian of a nodal indicator of interest) thus improving the discretization quality of the crack obtained and thereby optimizing the simulation cost. In this sense, the procedures for mapping nodal and internal variables as well as the calculation of the nodal variable of interest will be discussed. As far as the studies of natural disasters are concerned, especially those related to free-surface water flows such as tsunamis, one more level of coupling between the aforementioned method FEM-DEM and one Computational Fluid Dynamics (CFD) formulation commonly referred to as Particle Finite Element Method (PFEM) has been implemented. With this strong coupled formulation, many cases of wave impacts and fluid flows have been simulated against solid structures such as walls and dikes, among others.

Abstract

The results of a predictive analysis of the mock-up of a reactor containment building, based on computer numerical simulation, are presented in this paper and compared with the results obtained in the context of the VeRCoRs project during the 2015–2018 experimental campaign. The analysis is based on the Serial-Parallel Rule of Mixtures theory applied on a three-dimensional finite element model of the building. All the singular parts of the structure (two buttresses, the main penetrations, the gusset, etc.) and the complete prestressing tendons system are included in the structural model. The non-linear constitutive models used to describe the behaviour of the concrete, reinforcing steel and the tendons are formulated. A description of the Serial-Parallel Rule of Mixtures algorithm is also given. The structural response computed for the successive pressure tests applied on the mock-up are compared with the monitored structural behaviour. Finally, results for a simulation considering the aging of the tendon system during 40 years are shown and discussed.

Abstract

The main purpose of this paper is to develop a reliable method based on a three-dimensional (3D) finite-element (FE) model to simulate the constitutive behaviour of reinforced concrete structures strengthened with post-tensioned or pre-stressed tendons well beyond the elastic domain. The post-tensioned concrete is modelled as a composite material whose behaviour is described with the serial-parallel rule of mixtures (S-P RoM) (Rastellini et al., 2008; Martinez et al., 2008; Martinez et al., 2014 [3]) and the nonlinear behaviour of each component is accounted for by means of plasticity and damage models. 3D FE models were used, where the nonlinear material behaviour and geometrical analysis based on incremental-iterative load methods were adopted. Several examples are shown where the capabilities of the method on large scale structures are exhibited taking into account the self-weight, the post-tension load and different pressure loads. A new metric for computing the crack opening displacement inside a finite element is proposed.

Abstract

The main purpose of this paper is to develop a reliable method based on a three-dimensional (3D) finite-element (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 post-tensioned concrete is modelled as a composite material whose behaviour is described with the serial-parallel rule of mixtures (S/P RoM) (Rastellini et al, 2008; Martinez et al., 2008, 2014) 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 linear steel tendon and for a parabolic pre-tensioned steel tendon embedded. Some viscoelastic cases are presented 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.

Abstract

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 Zarate2D. 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 4-noded linear tetrahedron elements correctly captures the onset of fracture and its evolution, as shown in several 3D examples of application.

Abstract

This document explains the operation of the user interface of the FEM2DEM program to analyse two-dimensional solids using the simple FEM-DEM procedure proposed by Zarate & Oñate [A simple FEM–DEM technique for fracture prediction in materials and structures. Comp. Part. Mech. (2015) 2: 301-314] that is used to predict the initiation and propagation of fractures .

Abstract

Este documento explica el funcionamiento de la interface de usuario del programa FEM2DEM para analizar sólidos bidimensionales utilizando el sencillo procedimiento FEM-DEM propuesto por Zarate & Oñate, ( A simple FEM–DEM technique for fracture prediction in materials and structures. Comp. Part. Mech. 2015  2: 301-314 ) que se utiliza para predecir el inicio y la propagación de fracturas .