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Frequently Asked Questions (FAQ)
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AnswerIf there are the identical settings defined in the main program, the missing consideration of the material-related partial safety factor in the load case is often the reason (Figure 01).In the RF‑/STAGES add-on module, all calculations are always carried out in consideration of the partial safety factor. If this is not considered, it must be set specifically for the material.
First, please note that the local deformations of surfaces always refer to the undeformed structural system. Therefore, in the case of a multi-story building, the deformations of the top floor also include the deformations of the lower floors, as shown in Figure 01 on the left.
Figure 01 on the right shows the corresponding bending moment m‑y. It is identical for the floors, as expected for this simple model. In such a case, the partial calculation of the individual floors is not a problem, because the relative deformation seems to be the same for each floor.
However, it becomes a problem if the supporting elements are subjected to different load, or if there is a different stiffness of the supporting elements within one floor. Figure 02 shows the bending moment m‑y of such a structural system. It is apparent that the distribution shows the greatest differences especially between the bottom floor and the top floor. In this particular case, the internal columns with less rigid cross-section were entered in addition to the corner columns. For this reason, the relative deformation increases more with each additional floor in the middle than at the corner columns.
In reality, this structure cannot exist in this way because the floors are manufactured one after the other and thus the deformations (for example, due to self-weight) are compensated from one floor to another. Thus, it is a specific construction stage problem. Therefore, the question is if the effects can be neglected or if it is necessary to analyze the results with the RF‑STAGES add-on module, for example.
AnswerThere is no general answer to this problem. In the RF‑/STAGES add-on module, however, there is a specific feature regarding the structural system. Similar to some other add-on modules, such as RF‑/STEEL Warping Torsion, it is possible to consider the structural system detached from the main program. Thus, there are some advantages regarding the definition of construction stages, and so on. However, this possibility means that the modifications in the main program RFEM or RSTAB are not updated automatically with these add-on modules. Such an update would inevitably lead to incorrect calculations and is therefore blocked.
AnswerThe option controls how new structural elements in the construction stages are applied to the already existing deformed structure.Initial position:The new elements are applied with the orientation to the initial position, that is, to the provided geometry. The deformations are compensated throughout the construction process. In theory, there is a buckling in the geometry (Figure 02 1.)Tangential:The new elements are applied with the orientation of the already existing deformed elements, that is, tangential to them. The deformations are not compensated throughout the construction process. In theory, there is no buckling in the geometry (Figure 02 2.)
In RF-STAGES, the temporary loads in the respective structural state are calculated only linearly, according to the linear static analysis. The permanent loads that are implemented into the system will be -according to 3rd order theory- subject to nonlinear calculation. In the combinations that can be created in the add-on module, the results of the individual load cases are combined.
AnswerIt is currently not possible to display a concrete-concrete composite cross-section. For this, the structural state calculation must be coupled with the concrete cross-section solver. We are currently working on the possibility that this will be possible in future versions.
Basically, you should pay attention to the following points:
The structure in RF‑STAGES and RFEM may differ due to the definition in RF‑STAGES. Therefore, the structure in RF-STAGES may be different than in RFEM. In order to find the instability at a certain construction stage, it is necessary to model the structure in this construction stage in RFEM and take it into account separately. In this context, it should also be noted that the entries are not synchronized between RFEM and RF-STAGES. For example, a member end hinge removed in RFEM is not automatically removed in the RF-STAGES model.
Method of Analysis
RF-STAGES calculates permanent load cases according to the large deformation analysis. As a result of this analysis, instabilities may occur which are not present in a load case when calculating according to the linear static analysis (critical load problems), for example.
Special Structural Elements
Some of the structural elements available in RFEM are not supported in RF‑STAGES. These structural elements can also cause the instability in certain cases. The following structural elements are not fully supported in RF‑STAGES:
- Line hinges
- Member elastic foundations
- Sets of members
- Nodal releases
- Line releases
- Surface releases
- Nodal constraints
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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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