RF-CONCRETE Deflect | Design
The deformation analysis according to the approximation method defined in standards (for example deformation analysis according to EN 1992-1-1, 7.4.3) applies to the calculation of so-called effective stiffnesses in the finite elements in accordance with the existing limit state of the concrete with or without cracks. These stiffnesses are used to determine the surface deformation by repeated FEM calculation.
The effective stiffness calculation of finite elements takes into account a reinforced concrete cross-section. Based on the internal forces determined at the serviceability limit state in RFEM, the program classifies the reinforced concrete cross-section as "cracked" or "non-cracked". If the tension stiffening at a section should be considered as well, a distribution coefficient (according to EN 1992-1-1, Eq. 7.19, for example) is used. The material behavior of the concrete is determined as linear-elastic in the compression and tension zone until the concrete tensile strength is reached. This is reached exactly in the serviceability limit state.
When considering the creep and shrinkage, the effective stiffnesses are determined at the "cross-section level". The influence of shrinkage and creeping in statically indeterminate models is not considered by this approximation method (for example, in the case of structures restrained on all sides, tensile forces from shrinkage strain are not determined and have to be considered separately). In summary, RF-CONCRETE Deflect calculates deformations in two steps:
- Calculation of effective stiffnesses of the reinforced concrete cross-section assuming linear-elastic conditions
- Calculation of deformation using the effective stiffness with FEM