Non-intrusive analysis of damaged zone of concrete structures for real cracks description
Résumé
The analysis and prediction of the degradation process and cracking of concrete structures with numerical models is an important issue in the field of civil engineering. In order to describe the global behavior of a structure composed of quasi-brittle material as well as local fields, a continuous approach using nonlinear constitutive law (e.g. damage, plasticity,…) remains the most efficient one regarding the computational time. However, one has to consider additional tools to extract discrete information about cracks like spacing and openings from these computations. The objective of this research is to propose tools capable of extracting local information such as cracking using two post-treatment methods of a global finite element analysis. First, in the proposed method, a global non-linear finite element analysis of the whole structure is performed. This analysis reveals the zones of degradation that are to be reanalyzed via a local analysis using two post-treatment methods. The first method combines a topological search method used to locate cracks developed by Bottoni et al. [1] and a continuous/discontinuous approach used to compute the crack opening initially proposed by Dufour et al. [2].. It consists in comparing the computed strain fields, with the analytical one derived from the displacement profile described as a strong disconti-nuity. Both strain fields are regularized using a Gaussian function. The crack opening can then be adjusted so as to reduce the gap between the regularized strain field and the regular-ized strong discontinuity strain field. Furthermore, a general formulation of these tools for 2D and 3D problem is proposed in this work. The direction of the mode I crack at a point is determined as the one which maximizes the crack opening along the associated 1D profile. The second method is a non-intrusive reanalysis at the local scale performed with a discrete model in order to extract fine information about crack opening. A region of interest (ROI) corresponding to the damaged area obtained from the global analysis is defined. Then, the loading steps corresponding to the steps of reanalysis are determined, where boundary conditions are extracted from the continuous displacement field and applied on the non-free surfaces of the ROI. The material is described with a discrete element approach based on an assembly of polyhedral particles linked by Euler-Bernoulli beams with brittle behaviour. Further details concerning the discrete model used at the local scale can be found in [3]. The displacement fields obtained from the FE analysis are compared to the experimental data provided from the post-processing of the actual test in order to analyze the concordance of the results on the global scale.