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Frequently Asked Questions (FAQ)
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AnswerIf identical settings are defined in the main program, the failure to consider the material component safety factor in the load case is often the reason (Figure 1).In the RF-/STAGES module, all calculations are always carried out taking into account 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 are always related to the undeformed system. Therefore, for a multi-storey 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 no problem, because the relative deformation seems to be identical for each floor.
However, it becomes problematic if the supporting elements are loaded differently or if the stiffness of the supporting elements within a floor is different. Figure 02 shows the bending moment m-y of such a system. It is apparent that the distribution, especially between the bottom floor and the top floor, shows the greatest differences. In this particular case, internal columns with less stiff cross-section were added 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 will not 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 typical structural state problem. The question arises, therefore, of whether the effects can be neglected or if, for example, it is necessary to analyze the results with the add-on module RF-STAGES.
There is no general answer to this problem. In the RF-/STAGES add-on module, however, there is a particularity 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 structural states, etc. However, this possibility means that 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.)
AnswerIn RF-STAGES, the temporary loads in the respective construction stages are calculated only linearly, according to the linear static analysis. The permanent loads that are embossed into the system become nonlinear, according to Theorie III. Order, calculated. In the combinations that can be created in the add-on module, the results of the individual load cases are combined.
AnswerAn illustration of a concrete-concrete composite section is currently not possible. For this purpose, the construction condition calculation must be coupled with the cross-section solver of the concrete design. We are currently working on this 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 release 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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