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Frequently Asked Questions (FAQ)
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AnswerThere are a lot of possibilities to define a member to a surface. One is to move the surface by a small amount out of the original plane and add coupling on it. The workflow is demonstrated in the video.
AnswerThe cause may consist in the definition of member eccentricities. For a better overview, the origin lines are automatically hidden for eccentric members. In some cases, it may appear that a member end is not sufficiently supported (see Figure 01, left). However, the meshed line acts in the background. This can clearly be displayed by hiding the members in the Display navigator (see Figure 01, right).In Figure 01, the line at the common node has not been geometrically separated. For this reason, there is no graphical connection line representing the eccentricity, which would result in this case. However, because of the setting displayed in Figure 02, the node is still meshed with the vertical member.To visualize the graphical connection line, it is recommended to divide the member or line at this node (see Figure 03).
In the case of a ground failure analysis or soil contact stress analysis, the "equivalent surface" is determined in RF‑/FOUNDATION Pro in order to calculate the soil contact stress.If the foundation dimension is smaller than twice the load eccentricity "e," the "equivalent surface" or the "effective foundation" cannot be determined. In this case, you receive the corresponding error message.In most cases, the problem is that a user has entered too small dimensions of the foundation plate.To remedy the problem, you can manually set greater dimensions. Or select the "Dimensioning" feature.
AnswerThe axes, to which the support rotations and support eccentricities refer, are preset to the local member axes, which can be displayed with the button under the partial view. However, they can also be switched to the global axis system.
The setting of the load application specified in the Details refers to the principal axes of the respective cross-section. For a Z-section as an example, a box with nine edge nodes is set around the cross-section. The load application is then always related to the rotated principal axis angle and the corresponding eccentricities.
In a 2D model XY with the degrees of freedom (uz/fx/fy), no eccentricity can be defined. The eccentricity usually results in an axial force that is not covered by these degrees of freedom.
You should also be careful when using ribs. In contrast to the 3D model, the effective width also changes the stiffness of the structure.
Therefore, it is generally better to calculate the downstand beam structures in a 3D model.
AnswerFor rod end joints where the reference system is related to the local rod axes, the joint is placed directly on the rod end or rod end. If the joint is to act directly at the node, the reference system must be related to the global axis system.
There are basically two options:
- The use of member eccentricities, see the article Considering eccentricities of members and surfaces
- In the case of, for example, differently defined member hinges in combination with different dimensions of offsets, the use of couplings or rigid members may help, see Figure 1
In Window 2.2 "Member Loads," you can define the eccentricity of the load by scrolling to the right in the table.
By using a button, you can also graphically select the stress points of a cross-section and thus define the eccentricity on the basis of the cross-section (see figure).
Since program version 5.19, you can directly consider the eccentric load introduction in RFEM by using the member loads (see Figure 1). The eccentric load introduction can be used for the load type "Force".
Alternatively (for example in RSTAB), a coupling by means of a rigid member can be defined to take account of external concentrated loads that act eccentrically on the member. The rigid member is to be connected perpendicularly to the corresponding member. The length of the rigid member corresponds to the amount of the eccentricity (see Figure 2).
Alternatively, you can enter the torsional moment due to the eccentric load introduction as external loading (also for eccentric member loads). Thus, the eccentric action would be taken into account and the definition of a rigid member would not be necessary (see Figure 3).
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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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