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Frequently Asked Questions (FAQ)
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AnswerIn RFEM, the easiest way is to use the "Plane Surfaces" → "Annulus" feature. This allows you to model the reinforcement rings very quickly and easily. Then you can extrude the inner line into a surface, the chimney is already generated. Now, the existing annular surface is copied upwards and the corresponding stiffeners are modeled. You can use the "Rotate" command to distribute the stiffeners over the chimney perimeter.
Since a surface is a 2D element and therefore the transition from surface to solid is a line, singularities may occur here. Especially the moments m-y and m-x may cause some problems.
The best way to create the transition consists is to use rigid members, as shown in Figure 01.
In this option, the rigid members cover the height/thickness of the surface, and thus ensure a clean introduction of the moment into the solid. Furthermore, the rigid members must protrude into the surface; the depth has been selected to be a half of the surface thickness.
Figure 02 shows the calculation results. The model without the rigid members has a large deformation, which illustrates the effect. However, the model with the rigid members shows the same deformation as the pure surface model or solid model in some cases.
AnswerThe software features allow you to consider the decline of loads in RFEM/RSTAB, and to design the following member types in the add-on modules:
To prevent the automatic division of the existing member, it is necessary to disable the option "Auto Connect Lines/Members" in the shortcut menu that you can open by right-clicking the model window.
- Single member: A member has two nodes, one at the beginning and one at the end of the member. It is possible to connect several single members to create a continuous member or a set of members.
- Continuous member without intermediate cutting at the nodes
The modeling of planar structural components such as glass panes is generally only possible in RFEM.
If it is necessary to define the stiffening effect of a pane in a particular case, it can also be simulated in RSTAB.
Figure 1 shows a frame that is assumed to be stiffened by a plate.
Since members in RSTAB are the only possible structural components, the plate is simulated by means of members.
First, you have to decide, where the frame should be supported. The nodes have to be inserted just there. To insert nodes, it is recommended to equally divide the respective members with the function 'Divide Member' (right-click the member -> 'Divide Member'). To simulate a stiffening rigid pane, it is now possible to model a framework consisting of rigid members/couplings.
AnswerIf the load-bearing capacity of the wall surface is neglected and only applied to the ceiling as a load by using a line load, it would result in very large deformations.
If the nonlinear property of the masonry is not considered, it would result in very small deformations.
In principle, there are three options available in RFEM.
- Line release: Vertical compression forces are only transferred. In this case, the nonlinear property is only applied for the force transmission directly to the connection line of both surfaces.
- Nonlinear material "Isotropic Masonry": In this case, the tension stresses in the x- and y-direction (that is, vertical and horizontal) are reduced iteratively to the specified limit values by reducing the stiffness. Using this model, it is possible to represent the behavior of a masonry wall that is closest to reality, because the tension stresses are reduced in the direction of the mortar joints. This requires the RF‑MAT‑NL add-on module.
- Nonlinear surface stiffness type "Membrane without tension": In this case, the tension stresses in the principal stress direction are reduced iteratively by reducing the stiffness.
AnswerWhen modeling a structure, you should avoid the areas with double stiffnesses. If you model a downstand beam and a wall at the same location, these elements split the load application. The disadvantage of separating the members on the wall perimeter is, that the singularities occur at this location. Moreover, the area of the load application from the rib to the wall is at the ceiling height.Thus, there is no ideal solution in this combined modeling from members and surfaces.In the case of small models, it would be possible to model the downstand beams and carry out the design by means of result beams.
AnswerYes, it is possible. The FAQ video shows step by step how to create a model of such a component with quadrangle surfaces.
AnswerThe reason for this message is that you are in viewer mode. When installing RFEM or RSTAB, a viewer version is automatically installed in addition to the normal version. This will appear as an additional icon on the desktop. In this mode, files with results can be opened, but no changes can be made.
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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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