Load-deformation curves for reinforced concrete bcams subj ected to bending show size effects due to tensile failure of the concrete at early stages in the failure process and due to compression failure of the concrete when the final failure takes place. In this paper these effects are modelled using fradure mechanical concepts, and size effects of the models are studied and compared with experimental results. KEYWORD S Size effect, bending behaviour, reinforced concrete, minimum reinforcement, rotatianaJ capacity, fracture mechanics. .
Brincker et al. after the concrete tension failure peak seems to be well estimated by the model, indicating that it seems reasonable to assume a constant fridiorral shear stress in the debonded zones at each side o f the crack. References l.
The main object of the research work presented in this paper is to establish design tools for lightly reinforced flexural concrete members subjected to bending load. An analytical model for predicting the load deflection curve is established and compared with experimental results. The main focus will be minimum reinforcement requirements and the related size effects. The main idea of the analytical model is to assume that the response of the structure can be described by the cracking response located within a fracture band. Outside the fracture band Bernoulli-Euler beam theory is assumed. The constitutive model for the concrete is based on the idea that the initial part of the stress crack width relation can be described by a linear relation between load and crack width, taking into account the stresses caused by aggregate interlocking. The model follows ideas previously used by other researchers in order to describe the fracture mechanics of concrete beams. These ideas are extended in this model to take into account the pullout of the reinforcement.
In this appendix the fail ure behaviour of lightly reinforced concrete beams is investigated. A numerical model based on the fictitious crack approach according to Hillerborg [1] is established in arder to estimate the load-deflection curve for lightly reinforced concrete beams. The debonding between concrete and reinforcement is taken into account by introducing a debonded zone with constant shear frietion stress. Results are presented for material models representing normal strength concrete (two degrees of brittleness) and high strength concrete. The properties of the model are investigated and the results of the model are compared with results from experiments.
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