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2.7.1 Basic Material and Geometric Assumptions
Basic Material and Geometric Assumptions
For the deformation analysis with RF-CONCRETE Deflect, a linear-elastic compression and tension behavior of reinforcing steel is assumed. In the process, we apply a linear-elastic compression behavior and a linear-elastic behavior for concrete until the tension strength is reached. Such assumptions are sufficiently accurate for the serviceability limit state. If the provided stress exceeds the tensile strength of concrete, damage develops according to EN 1992-1-1, clause 7.3.4.
The calculation uses a simple isotropic model of fracture mechanics that is defined individually in the two directions of reinforcement. From an engineering point of view, the material stiffness matrix is calculated through interpolation between the uncracked (state I) and cracked state (state II) according to EN 1992-1-1, clause 7.4.3, Equation (7.18). Thus, the reinforced concrete is modeled as an orthotropic material. All laws of damage development can take the tension stiffening effect and simple long-term effects (shrinkage and creep) into account.
The calculation of the material stiffness matrices is implemented for the model types 2D - XY (uZ / φX / φY) and 3D. For the model type 3D, the eccentricities' influence of the ideal centroid (see below) is additionally considered in the stiffness matrix.