RFEM – Online Manual

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RFEM – Online Manual

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11.8.1 General Features

General Features

Settings for load generation

Many dialog boxes provide the button (see Figure 11.184) for opening the Settings for Load Generation dialog box, used to control the tolerance for the integration of nodes into the load plane and to correct the generated loads.

Figure 11.178 Settings for Load Generation via Plane dialog box

These settings apply for all member load generators. The Tolerance determines the conditions under which members or nodes are considered as belonging to a plane or line. Specifications are possible by entering an angle or a distance. If nodes lie within these defined thresholds, RFEM recognizes the cells and generates the loads.

The Correction of Generated Loads dialog section allows for a comparison between the available area loads and the determined member loads. The check sums are displayed in the dialog boxes that appear after the load generation, before the final conversion into member loads (see Figure 11.188). In case of minor differences, you should make a correction of the distribution in accordance with the moment equilibrium. The following applies:

Table 11.14

Equilibrium of forces

Equilibrium of moments

where r = (x, y)

Distance to centroid of cell

When correcting generated loads in accordance with the moment equilibrium, the moment is formed from the area loads to the centroid and then compared with the moment from the member loads to the centroid. As a simplification, you may imagine the moment correction to be a recalculation of the support forces. This support force is then applied to the member as a line load. This correction option allows you to create trapezoidal member loads from variable area loads, for example.

The Usage of Non-loaded Members for Cell Generation dialog section primarily concerns members that lie in an inclined position within the model. In the course of the load generation, the total area to be loaded is determined first. Then RFEM examines, which members enclose cells. The cells are subsequently subtracted from the total area. When excluding a member from the loading (Remove Influence from members option, see below), RFEM relocates its load to the remaining members of the plane or cell.

The three options are illustrated with an example of a platform construction. We only want to apply traffic loads to the members that run in direction X. Like the Y-parallel members, the inclined member is excluded from the load application, but it does affect the creation of member loads depending on the setting.

Figure 11.179 Platform construction with cells for load generation
    • Do not use any member:
    • The load is applied uniformly to the edge members and the intermediate members. With this setting, all excluded members are ignored, that is, internally applied for load distribution. After calculating the cell area, the load is distributed to the allowed members of the cell.
Figure 11.180 Result for Do not use any member
    • Use all members:
    • All unloaded members are excluded for the load generation. There is still a problem with the load distribution because of the large, generated cell 2.
Figure 11.181 Result for Use all members
    • Use members parallel to boundary:
    • With this, it is possible to exclude members that lie in an inclined position. If the limit angle φb between members is restricted to 44.55° in the Settings dialog box (see Figure 11.178), the load is generated as expected.
Figure 11.182 Result for Use members parallel to boundary
Modifying generated loads retroactively

After confirming a generator dialog box, the generated loads are transferred to load table 3.15. The Generated Loads entry additionally appears in the Data navigator (see Figure 6.57). In the load shortcut menu and the Display navigator, you can set if the generated loads are displayed as a surface load symbol or Separately as member loads.

The generator parameters are not lost because the original dialog boxes remain accessible as input objects for changes. To open the initial dialog box once more, double-click one of the entries in the navigator or double-click a generated load in the work window. There you can adjust the parameters.

If you want to treat the generated loads as isolated load objects, you have to release the loads from the concept and split them into their components. This step can be accessed in the load shortcut menu that you open by right-clicking a generated load. The Disconnect Generated Load function (see Figure 11.183) allows you to create the individual loads.

Figure 11.183 Shortcut menu of generated loads

You can also use the shortcut menu of the generated loads in the Data navigator.