G. Meschke:
"Synthese aus konstitutivem Modellieren von Beton mittels dreiaxialer, elasto-plastischer Werkstoffmodelle und Finite-Elemente-Analysen dickwandiger Stahlbetonkonstruktionen";
Supervisor, Reviewer: H.A. Mang, H. Reiffenstuhl; Vienna University of Technology, Vienna, Austria, 1989.
This thesis contains a comparative evalutaion of various elasto-plastic constitutive models for concrete and an investigation concerning the influence of different material models on the result of finite-element ultimate load analysis of thick-walled reinforced concrete structures.After a systematic classification of existing triaxial elasto-plastic models, a numerical evaluation of four selected models is carried out. It is based on a comparison of numerical results, stemming from a relatively large number of load paths up to failure, with corresponding test results. The chosen models are the nonassociated model by Han and Chen, the associated model by Glemberg, a bounding surface model by Chen and Buyukozturk and a new hypoplastic model, proposed by the author, which is characterized by a closed bounding surface and by the vanishing of the elastic region.
With the exception of the constitutive model by Chen and Buyukozturk, the material models are implemented in the multi purpose finite-element program MARC. Three structural members, each one representing a different state of stress, are investigated. In the post failure region, concrete is modeled as an ideally-plastic material. Crushing will occur, if a criterion based on stress invariants is satisfied.
The numerical investigation of a thick-walled corbel elucidates the insignificance of constitutive modelling of concrete in the prefailure regime, relative to the significance of modelling of interface shear transfer across cracks by means of different shear retention factors. The second numerical example pertains to a reinforced concrete ring under radial loads. It is found, that the specific characteristics of the different constitutive models only have a minor influence on the predicted response of this kind of structure. On the basis of a scalar crushing cirterion, good agreement between the predicted ultimate load and the experimental result is obtained by all three models. Finally, analyses of a cylindcrial concrete specimen subjectes to highly concentrated loading are carried out. The numerically obtained response is strongly influenced by the type of constitutive model used in the analysis. The predictions obtained by the material model by Han and Chen and by Glemberg do not reflect the experimental performance of the cylinder. The load-penetration relationship as well as the ultimate load predicted by the new hypoplastic model, however, are found to agree well with the corresponding test results.
Keywords: @dissertation