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Non-Linear Finite Element Analyses of Reinforced Concrete with Large Scale Elements: Including a Case Study of a Structural Wall
Norwegian University of Science and Technology, Faculty of Engineering Science and Technology, Department of Structural Engineering.
2014 (English)MasteroppgaveStudent thesis
Abstract [en]

The accuracy of large scaled elements in nonlinear finite element analyses (NLFEA) of reinforced concrete is investigated. A much used finite element analysis design procedure used to design large offshore concrete structures is presented and suggestions for the utilization of NLFEA in the process is given. Means to obtain effective use of NLFEA are discussed and the importance of large elements to minimize the computational cost is stressed. The use of large elements is investigated through a case study of a structural wall. The wall is analyzed using medium scaled elements that should be able to predict the behavior well, and by use of large elements. Both analysis results are compared with experimental results. The finite element models are created as they would in a design situation and the analyses are conducted without tweaking of the material parameters. State-of-the-art material models are chosen that accurately describe the most important material characteristics of reinforced concrete. A short presentation of the Smeared crack approach for finite element modeling of concrete is given. Both a fixed and a rotating crack model is used. The results of the analyses reveal a poorly predicted ultimate load carrying capacity of the structural wall and it is found that the missing inclusion of the volumetric expansion effect of concrete is the main cause. No significant difference is found between the fixed and the rotating crack models, a finding that is attributed to the fact that no rotation of the stress field in the structural wall is seen before the peak load. A higher load capacity is found when using large scale elements. It is believed that the higher capacity is caused by the inability of the large elements to pick up the most extreme compressive stresses in the compressive zone. Thus the failure of the compressive zone is delayed and a higher load capacity is found. In the first phase of the deformational response the predicted behavior of the wall in the large scale analyses is found to be stiffer due to non-localized cracks, as compared to the medium scale analyses where a localized crack pattern is observed. When the crack pattern is progressed the difference is negligible. It is found that the all-over prediction of the wall behavior in the large scale analyses is good. The stiffness for high load levels is very accurate and the failure mode is correct. If part of a larger structure the predicted behavior of the wall would probably allow for finding of the correct distribution of forces in the structure and the cause and progression of failure. Thus the use of large elements is found to be possible in a design situation. However, a lot of work remains to be done before such use can be done confidently. Suggestions for further work are given.

Place, publisher, year, edition, pages
Institutt for konstruksjonsteknikk , 2014. , 102 p.
URN: urn:nbn:no:ntnu:diva-26407Local ID: ntnudaim:12062OAI: diva2:747485
Available from: 2014-09-16 Created: 2014-09-16 Last updated: 2014-09-16Bibliographically approved

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