M.A.N. Hendriks

Development of guidelines for nonlinear finite element analyses of existing reinforced and pre-stressed beams

ABSTRACT The Dutch Ministry of Infrastructure and the Environment initiated a project to reevaluate the carrying capacity of existing bridges and viaducts through the use of nonlinear finite element analyses (NLFEA) which are more and more becoming an usual instrument of calculation in the daily design procedures. Numerical simulations of several case studies taken from experimental programs have therefore been performed in order to assess and criticize the finite element approaches. In this paper guidelines for nonlinear finite element analyses are proposed to optimize the results obtained from numerical simulations of reinforced and pre-stressed beams in order to reduce model and users factor. The numerical results are also compared with analytical procedures proposed by the new Model Code 2010 which proposes different numerical and analytical procedures to evaluate the carrying capacity of existing structures based on the definition of different safety levels.

Numerical homogenization of the rigidity tensor in Hooke's law using the node-based finite element method

Combining a geological model with a geomechanical model, it generally turns out that the geomechanical model is built from units that are at least a 100 times larger in volume than the units of the geological model. To counter this mismatch in scales, the geological data models heterogeneous fine-scale Youngs moduli and Poissons ratios have to be “upscaled” to one “equivalent homogeneous” coarse-scale rigidity. This coarse-scale rigidity relates the volume-averaged displacement, strain, stress, and energy to each other, in such a way that the equilibrium equation, Hookes law, and the energy equation preserve their fine-scale form on the coarse scale. Under the simplifying assumption of spatial periodicity of the heterogeneous fine-scale rigidity, homogenization theory can be applied. However, even then the spatial variability is generally so complex that exact solutions cannot be found. Therefore, numerical approximation methods have to be applied. Here the node-based finite element method for the displacement as primary variable has been used. Three numerical examples showing the upper bound character of this finite element method are presented.

A Hybrid Method to Determine Material Parameters of Composites

This paper presents a method to determine parameters in constitutive equations, used for the description of the mechanical behaviour of composites. The method is based on: numerical analysis, strain distribution measurements and systems identification techniques. The method is especially suitable to study the behaviour of inhomogeneous materials. By means of a simulation it will be shown that for a solid with a varying fibre direction it is possible to estimate the stiffness parameters as well as the local fibre directions from one single test.

Elasto-Plastic Design and Assessment of Pipelines: 3D Finite Element Modeling

A common finite element modeling approach for buried pipelines is the combined use of beam and spring elements. Typical loads are soil settlements, temperature variations, internal pressures, neutral topsoil loads and traffic loads. The beam elements represent the pipeline; assemblies of spring elements represent the surrounding soil comprising an elasto-plastic bedding and friction. The choice for such finite element models is a pragmatic one. The models are relatively easy to construct and the analyses can be performed within reasonable calculation time on an average PC. From a mechanical point of view the problem of a buried pipeline subjected to subsidence, or an offshore pipeline subjected to sand waves, is of a full 3D nature. Beam elements and spring elements only partly incorporate full 3D effects. In practice the common finite element models are therefore enhanced to take into account 3D effects that would be missed otherwise. A major point is the distinction between beam action and cross sectional behavior of pipes in straight and curved sections and their mutual interaction.

Non-Linear Finite Element Analyses of Existing Reinforced Concrete Bridge Beams

Three years ago, the Dutch Ministry of Infrastructure and the Environment initiated a project to re-evaluate the carrying capacity of existing bridges and viaducts (e.g. reinforced and pre-stressed concrete beams and slabs). Due to the increase of traffic and the reallocation of emergency lanes to traffic lanes, the safety verification of some concrete structures are not satisfied if the usual analytical procedures are followed. Nonlinear finite element analyses (NLFEA) are considered as one of the alternatives for the verification of the structural carrying capacity. Building codes hardly provide specific guidance on how NLFEA should be carried out and reported. Within the project guidelines for NLFEA have been developed in order to reduce model and user factors. The aim of the project well fits with the philosophy of the new Model Code 2010 (MC2010) that proposes analytical and numerical calculation methods for the evaluation of the design resistance of reinforced concrete (RC) structures. In the paper four reinforced concrete beams, characterized by different failure modes, have been analyzed through the analytical and numerical procedures proposed by the Model Code 2010 and following the Dutch guidelines. The results obtained have been compared with the experimental results available in literature. Furthermore in order to focus on the main sensitive parameters that influence the results obtained from NLFEA and to obtain reliable and, at the same time, safe results, parametric studies have also been carried out on the beams. The main indications of the guidelines for reinforced concrete beams are presented in the paper.

3-D Finite Element Analysis of Early-Age Bridge Deck Cracking

Early-age bridge deck cracking is the single most prevalent distress on bridges reported by all of the state department of transportations. Although there have been many studies performed with regard to the cause of early-age deck cracking, the problem still exists. The early-age deck cracking due to restraint thermal stresses can be predicted using the 3-D finite element program DIANA. It simulates hydration of young concrete, shrinkage and cracks due to environmental conditions during the construction period and the restraint of the girders and adjacent structural elements. The analysis covers two stages. The first stage covers the construction period before the bridge is opened to traffic. The second stage starts after removing the formwork including just the bridge self-weight. Simulation results including time and crack initiation enable the understanding of cracking mechanism in young concrete as a first step to avoid early-age bridge deck cracking.

3D Finite Element Modeling of Buried Pipelines: On the Interaction of Beam Action of Pipelines and Cross Sectional Behavior

A common finite element modeling approach for buried pipelines is the combined use of beam and spring elements. Typical loads are soil settlements, temperature variations, internal pressures, neutral topsoil weight load and traffic loads. The beam elements represent the pipeline; assemblies of spring elements represent the surrounding soil comprising an elastoplastic bedding with friction. The choice for such finite element models is a pragmatic one. The models are relatively easy to construct and the analyses can be performed within reasonable calculation time on an average PC. From a mechanical point of view the problem of a buried pipeline subjected to subsidence, or an offshore pipeline subjected to sand waves, is of a full 3D nature. Beam elements and spring elements only partly incorporate full 3D effects. In practice the common finite element models are therefore enhanced to take into account 3D effects that would be otherwise omitted. A major point is the distinction between beam action and cross sectional behavior of pipes in straight and curved sections and their mutual interaction. This paper discusses the pros and cons of two possible finite element approaches which deal with this full 3D problem. In the final example it is illustrated that the two approaches gives similar results for the relatively simple problem of a buried bended pipe subjected to a temperature load and internal pressure.Copyright