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Frequently Asked Questions (FAQ)
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AnswerUnfortunately, the add-on module RF-CONCRETE Surfaces for RFEM 5 is not designed for the design of sandwich elements. Therefore, there are no essential designs for structural components like For example, the shear joint check. Regardless of whether it is a wall or a slab.The bending design, and in particular the check of the shear force resistance, is designed for constant cross-sections.You can model the sandwich elements as surfaces with a constant thickness and perform the design in RF-CONCRETE Surfaces. If necessary Additionally required designs would have to be performed separately.
AnswerNo, no basic reinforcement defined in RF-CONCRETE Surfaces is considered in the determination of internal forces in RFEM. In RFEM, the internal forces are determined with the modulus of elasticity of the selected concrete. The reinforcement amount has no influence (linear-elastic calculation, state I).The situation is different if you perform a nonlinear design in the serviceability limit state state II with the RF-CONCRETE NL add-on module. Here, you specify an available basic reinforcement that you want to consider for the nonlinear calculation in state II. In nonlinear design (available only for SLS), the determination of internal forces is carried out with the effective stiffnesses (state II). Thus, the defined reinforcement has an influence on the internal forces.You can evaluate these internal forces (from state II with the influence of the defined reinforcement) in the results of RF-CONCRETE Surfaces. See Figure 01 with the Results navigator of the RF-CONCRETE Surfaces add-on module.
AnswerNo, this is unfortunately not possible.The program concept of RF-CONCRETE Surfaces is designed in such a way that it is always necessary to place a reinforcement on the top and bottom layer.If necessary you can try to concentrate the individual reinforcement layers in the center of the surface. However, make sure that the individual reinforcement layers do not "touch" each other. Otherwise, an error message appears. See Figure 01.
AnswerPlease note that in the context of the nonlinear calculation, the reinforcement is not increased automatically. A nonlinear calculation is based on an already provided reinforcement. This provided reinforcement can result, for example, from the ultimate limit state designs or a defined ground reinforcement. The reinforcement applied for the SLS designs can be displayed graphically (see Figure 2).Cause of issue:If no reinforcement results from the ULS or the basic reinforcement in some areas, the serviceability limit state design is carried out without the applied reinforcement, and very high results may result, for example in the crack width.Solution to the problem:It should be ensured that there is a reinforcement in each zone of the structure. This can be implemented by applying a basic reinforcement (see Figure 3).
AnswerWhen exporting the non-linear stiffness from the module RF-CONCRETE Members or the module RF-CONCRETE surfaces, only the stiffness values are exported.The following results or effects are not exported with:
At the moment it is not possible to graphically export the exported stiffness in the RFEM.
- wane: The influence of shrinkage is not directly exported because shrinkage from the load and not on the stiffness side is taken into account. If, in the course of considering the shrinkage, a change in stiffness occurs (tearing open), this effect is of course also exported.
- Results from the NL calculation: Further results from the non-linear calculation, such as crack width or steel and concrete stress, are not exported.
AnswerIt is quite likely that the high deformations are caused by the consideration of shrinkage and the horizontal storage in the model.The shrinkage is taken into account internally on the load side as elongation, in which connection a failure due to the prevention of shrinkage is also possible. If the shrinkage is prevented by a non-displaceable horizontal bearing, forces are created which can lead to failure of the concrete and thus to a significant increase in deformation or even instability of the model.In this context, it is important that when using the nonlinear deformation calculation, the boundary conditions of the model are mapped as realistically as possible.
AnswerThis should be possible if only one combination is used in the non-linear calculation. Theoretical background is that RF-SOILIN can not consider several situations in parallel with different bedding parameters. It can only be considered a case. If several load situations are considered in RF-BETON NL, theoretically several systems with different stiffness result. In the context of RF-SOILIN this leads to a contradictory situation.
For the stability design of compression elements, you need the combination of RF-CONCRETE Members and RF-CONCRETE NL. The reason is the following:
First, the internal forces of the individual load combinations (second-order analysis + imperfection) are subjected to the linear-elastic calculation. For this, you basically only need RFEM.
Then, the cross-section design is performed in RF-CONCRETE Members with these internal forces determined linearly-elastically, and the required bending reinforcement is determined from these internal forces.
This bending reinforcement is then compared with the user-defined entries concerning the existing basic reinforcement or the minimum reinforcement and based on this, the reinforcement concept is generated (dialog box '3.1 Existing Longitudinal Reinforcement' of the module).
This existing longitudinal reinforcement is then used for the nonlinear design.
According to Section 5.8.6 (1), geometric nonlinearities must be taken into account according to the second-order analysis. However, the general rules for nonlinear methods according to 5.7 also apply.
In Sec. 5.7(1), 'an adequate non-linear behaviour for materials is assumed'. According to 5.7(4)P, the use of material characteristics which represent the stiffness in a realistic way but take account of the uncertainties of failure shall be used when using non-linear analysis.
This requires the RF-CONCRETE NL add-on module. Thus, the geometric and material nonlinearities are considered and the requirements of EC 2 regarding the ultimate limit state design are fulfilled.
Similarly, this method is also available in RSTAB in the CONCRETE add-on module.
AnswerThe angle of 90° between the reinforcement directions can only be changed if there is no serviceability limit state design performed by the analytical method. If the SLS is analysed nonlinearly, the angle can be adjusted.
To be able to calculate deformations in state II in RF-CONCRETE Surfaces, at least one load case or combination must first be selected in the "Serviceability Limit State" tab of the "1.1 General Data" window (see Figure 01).
In the lower part of the window, you can specify whether the "Analytical" or "Nonlinearity method" should be performed.
- If " Analytical ... " is selected, the option "Deformation with RF-CONCRETE Deflect" must be activated in the detail settings (see Figure 02).
- If " Nonlinear ... " is selected, you can also find the design of the deformations in the detail settings. The "Deformation" check box is activated by default (see Figure 03).
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