It may result in disturbing the earlier mentioned inequality. If different materials are used in a model and calculations (for example, with different classes such as concretes with different Young's modulus or Poisson's ratio), the coefficient value is corrected automatically. This coefficient can be interpreted (mainly for slabs subjected to unidirectional bending) as an elastic deflection multiplier. If properties of materials used during design are identical to those used in a model, then the value of the coefficient D / B > 1.0. Note: Stiffness factor X and Stiffness factor Y correspond to D/Bx and D/By, respectively. The weight for averaging is the ratio of moments acting on a given element in both directions. For further calculations, a weighted average of component stiffness values is used. As a result of these calculations, two stiffness values (different in most cases) are obtained for each finite element. The scope and method of calculating these stiffness values depends on detailed requirements of a given code. Stiffness calculations are carried out for two directions of reinforcement. The calculation algorithm for the equivalent stiffness (elastic) method is as follows:Īfter performing the structure analysis using FEM and calculating the required reinforcement area for the ultimate limit state, the serviceability limit state (as regards cracking calculations, stress limits, or other issues that may be considered locally) and the accidental limit state, stiffness for each finite element (FE) is evaluated in the program.
Such an approach comes down to linear scaling of individual elastic displacements by the global coefficient of stiffness reduction. Elastic displacements of i-th calculation point of a slabĭ - Slab stiffness assuming elasticity of the material (as in FEM calculations)ī - Equivalent stiffness of an RC plate, calculated considering element cracking, rheological effects, adherence of calculated reinforcement, etc. Real displacements of i-th calculation point of a slab which take account of cracking and calculated reinforcement
It has, however, no significant influence on extreme deflection values for a given panel. If a panel may not be treated as a structural element (it comprises more structure elements), deformation (deflection) maps should be treated with great caution. That combination is chosen for calculations for which there are maximum elastic displacements (positive and negative separately).
For a panel, these supports do not need to be continuous throughout the whole panel contour.ĭivision to panels does not affect the results of verification using the With stiffness update (FEM) method provided that loads, geometry and calculated reinforcement are the same.Ĭalculations are performed for a selected combination (separate for the lower and upper displacements) or a combination group, if that is required by the code (frequent, rare and quasi-permanent combinations). That panel should be defined within the limits set by the supports around it (similarly as spans which are limited by supports in the case of beams). It is recommended to model each floor segment where local extremes of deflections may occur as a separate panel. Influence of such disturbances on extreme values is not very significant, however deformation (deflection) maps should be treated with great caution. This may result in the influence of very distant elements on displacements of an analyzed FE. Such an assumption is correct if a panel can be identified with a structural element (span, floor segment), otherwise stiffness values averaged within a panel may be distorted. Displacements are calculated applying the Finite Element Method (FEM), then they are modified.Ĭalculations are performed separately for each panel. Changes of material stiffness due to cracking are considered. The algorithm for deflections of RC plates is based on the use of calculations of an isotropic elastic plate made of an elastic material.