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Frequently Asked Questions (FAQ)
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AnswerSimilarly to surfaces, there are various smoothing options for displaying the results of support reactions. For a nonlinear support, you should always select the actual distribution to display the results.
For surface supports, this option is only available if there is also the nonlinearity defined in the local z direction (failure if contact stress in z is negative/positive). In the dialog box where you can edit the nonlinearity, you can find the "Friction in plane xy" option.
This option works as shown in the graphic dialog box: The support in the x and y direction is fully accepted only when reaching the contact stress Tau (contact stress Sigma multiplied by the friction coefficient). It is necessary to reduce this linearly in advance.
In order to use this option, a support must be in the horizontal directions. It can be defined as fixed or with an elastic spring. If the spring is defined with 0, no support is considered even though a friction coefficient has been entered.
AnswerWhen defining nonlinearities, such as support failure under tension, it may happen that some load cases cannot be calculated. If these are the loads that cannot exist without other stabilizing loads, the problem resolution is simple: You can set the load cases to "Not To Be Calculated." As a result, the load combinations are only considered in the "Calculate All" option of the calculation process. This is possible because some loads can never appear without a dead load, for example.In the attached example, it is clearly evident that the structural system would buckle in the Wind load case, and thus no convergence is found. In contrast to this, it is possible to calculate the load combination, where the dead load and the wind are combined without any problem because the dead load stabilizes the system.
The difference between both material models is as follows:
In the Isotropic Nonlinear Elastic 1D material model, no plastic deformations are considered. This means that the material returns to its initial state after the load relief.
In the case of the Isotropic Plastic 1D material model, the plastic deformation is considered.
For both material models, the nonlinear properties are defined in an additional dialog box. When entering data by means of a diagram, it is possible in both models to define the distribution after the last step.
The Isotropic Nonlinear Elastic 1D material model allows for the anti-symmetric input of the stress-strain diagram (different for the positive and negative zone), whereas the isotropic Plastic 1D model only allows for symmetric input.
AnswerIn this case, the Calculation Method and the type of the 2D model are important.When using the analytical method (RF‑CONCRETE Deflect), it is possible to perform the calculation in 2D models. When using the nonlinear method (RF‑CONCRETE NL), the calculation for 2D XY (uZ/φX/φY) is not possible. In the nonlinear calculation, shrinkage is represented internally as strain load, which is not possible in this type of 2D model due to the limited degrees of freedom.Convert 2D to 3D ModelIn General Data, you can simply convert a 2D model into a 3D model. For the supports, all degrees of freedom not contained in the 2D model are fixed when converting to a 3D model (see the video).
AnswerThe differences resulting from the determination of the deformation in the cracked state can have various causes. In the case of deviations, you should check the following points:
Is the same calculation method applied?
RF-CONCRETE Deflect uses the analytical analysis approach according to EN 1992‑1‑1, 7.4.3.RF-CONCRETE NL uses the physically nonlinear analysis approach.You can find more information about the calculation methods in Chapter 2.7 and Chapter 2.8 of the RF‑CONCRETE Surfaces manual.
Is the same initial structure available?
If considering the underlying structural system as equivalent, the results of the linear calculation can be considered in the best way. The linearly determined deformation of the underlying combination should be approximately equal. Possible differences in the linear deformation may be increased in the cracked state in connection with the deformation analysis.
Are the same effects taken into account?
When comparing, make sure that the same effects, such as creeping and shrinkage, are taken into account (Figure 02).
Are the same initial values available?
In connection with the deformation analysis, you should further check if the same initial values are available. In this case, a special attention has to be paid to the fact whether the applied reinforcement (Figure 03) and the lever arm or the concrete cover are the same.
If you cannot find the cause after the fundamental examination, please contact our hotline.
AnswerThe load from the form-finding load case (FF) is fixed to the structural system 1.0‑times. If you want to factorize the dead load related to the combinations, it is possible to additionally create a permanent load case for the dead load with a 0.35‑fold load.
AnswerIf nodal supports are modeled on supported lines, this may lead to problems and incorrect definitions. Therefore, the following warning message appears in the plausibility check.Internally, the line supports and nodal supports are treated on each FE node. If there is a nodal support located on a line support, an FE node thus receives several support definitions. If the defined directions of the supports are not equal, this is not critical and the warning message can be ignored. If the same directions are defined several times, discrepancies may occur.In the case of a line support that is failing under the tension and a nodal support on this line, the tension force thus results in the FE node which, however, counts to the line support and to the nodal support.To avoid this behavior, it is possible to insert a short line without a support definition in the area of each nodal support. It may also be useful to model a tension bracket by using a newly defined member. The force transmission can then be adjusted by using the support of the member, the member type itself, and the member end release.In general, the support stiffenings should be estimated in a realistic way; in the example, rigid supports were assumed as a simplification.
When using the automatic arrangement of the reinforcement, make sure that the additional reinforcement is applied, if necessary, for the serviceability limit state designs in addition to the basic reinforcement. The default setting in the add-on module is selected in such a way that the required reinforcement from the ultimate limit state is also applied for the SLS.
You can select the reinforcement that is applied for the SLS in "Additional Reinforcement for Serviceability State Design." The Info button explains the individual options (Figure 02).
The reinforcement applied to the designs can be followed by using the "Selected Reinforcement for SLS Check" function (Figure 03).
The differences between the two modules are explained in this FAQ.
In the case of the same settings, there should also be the same results calculated in both add-on modules. However, this does not apply to the existing nonlinearities. The reason is that there are no nonlinearities considered in the RF‑/DYNAM Pro add-on module. If displaying the results in the Forced Vibrations add-on module, all nonlinearities are thus ignored. In contrast, the equivalent loads are calculated on a linear structural system, but the exported load cases are then calculated on a real structure in RFEM and RSTAB, that is, with all nonlinearities. This may lead to inconsistent results.
If you deactivate the nonlinearities for the exported load cases, you should obtain the same results.
The way of considering nonlinearities in the response spectrum analysis is described on the basis of tension members in this FAQ.
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Wind Simulation & Wind Load Generation
With the stand-alone program RWIND Simulation, wind flows around simple or complex structures can be simulated by means of a digital wind tunnel.
The generated wind loads acting on these objects can be imported to RFEM or RSTAB.
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