RFEM – Online Manual

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RFEM – Online Manual

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11.8.2.1

Member loads from area loads via plane

Figure 11.184 Convert Area Loads to Member Loads via Planes dialog box
Area Load Direction

Specify, whether the load acts perpendicular to the plane or globally related to the real or projected area. The dialog graphic in the bottom right illustrates the selected load direction.

Member Load Direction

The generated member loads can be set to be global or local loads (see Chapter 6.2). The difference is especially significant for nonlinear calculations.

Area of Load Application

There are two selection options. Select Full closed plane when there is a surface in the load plane between the members (e.g. wall or roof surface) that is not displayed in the RFEM model. In doing so, RFEM apportions the area load that acts on the entire plane to the members. However, if the construction consists only of members (e.g. lattice tower), select the Empty, on members only option. Then, only the effective or projected area that is provided by the member cross-sections as the "load application surface" is stressed. The load is applied in consideration of the member orientation.

Load Distribution Type

This section controls how the area load components are assigned to the members. Select Axes of angles for polygons that do not have a reflex angle. The intersection points of the bisecting lines are connected in such a way that application areas are created as shown in the figure on the left. In this way, it is possible to unambiguously distribute the area load to the members.

The angle axes method is not applicable for planes with reflex angles or for polygons. In such cases, set the load distribution type to Constant. In addition to the angle bisectors, RFEM also determines the centroid of the plane. If the intersection points of the bisecting lines lie in front of the centroid, triangular application areas are generated. If they lie behind the centroid, a line that is parallel to the member is drawn through the centroid, forming an application area with both angle bisectors.

Figure 11.185 Load distribution type Constant

Using this method results in areas not being considered or being applied twice. The missing or remaining amount is multiplied by a constant so that the sum of the area and member loads is equal.

The Combined option determines the application areas of triangles, quadrangles, and polygons according to the angle axes method, where possible. If the method cannot be used, RFEM automatically switches to the constant load distribution. The combined method is therefore set by default; RFEM automatically selects the appropriate method.

Area Load Distribution

The load can act on the area as a Uniform or Linearly variable load. It is also possible to define area loads that act freely Varying in direction of a global axis (e.g. height-dependent wind load). Use the button to open a dialog box where you can define the load parameters depending on the height levels.

Figure 11.186 Varying Area Load dialog box

In the left table column, enter the global ordinates of the Level; on the right, assign the respective values of the Area Load. The graphic visualizes the current state of input.

When freely variable loads are set, you have to select the correction of the distribution according to the moment equilibrium in the Settings dialog box (see Figure 11.178). Otherwise, constant member loads are generated.

Area Load Magnitude

When the load acts uniformly on the area, enter the load value into the enabled text box. For linearly variable loads, specify three node numbers with the respective loads. You can also use the button to graphically select the nodes in the work window.

Boundary of the Area Load Plane

Select the corner nodes of the plane to define the Boundary of the Area Load Plane. Use the button and click the relevant nodes one after the other in the work window. In doing so, the plane is marked in the selection color. The fully entered plane appears cyan in color. At least three nodes are required for defining a plane. The area does not need to be enclosed by lines or members on all sides.

It is possible to define different planes that appear in the Corner nodes list.

If the dialog box is opened repeatedly, the last entered planes may be preset in the Corner nodes list. To avoid unintentionally assigning double loads to these planes, it is recommended to empty the entire list with the button.

Remove Influence from members

In the Remove Influence from dialog section, you can exclude members from the load application (e.g. purlins, bracings). The selection is carried out member by member or by entering a member template that is [Parallel] to the load-free members. It is recommended to use the graphical selection using .

Click the button to open the Settings for Load Generation dialog box (see Figure 11.178). In it, you can adjust the tolerance for the integration of nodes into the load plane or correct the generated loads.

The [Assign load correction factors] button allows you to scale the loads for specific members. With it, you can, for example, consider the effects of continuity of a roof sheathing on the edge rafters in order to generate reduced member loads. The following dialog box appears.

Figure 11.187 Assign Correction Factors to Members dialog box

You can use the and buttons to select the members in the work window and scale them with a Factor.

Click [OK] to start the generation of member loads. An overview appears with information about the cells and loads.

Figure 11.188 Info About Conversion of Area Load to Member Loads dialog box

If inadmissible cells are listed, RFEM was unable to unambiguously assign the loads. Use the button to highlight the invalid cell in the graphic. To show a list of reasons for invalid cells, click the button. Often, removed borders of the cell (i.e. edge members excluded from load application) or crossing members that are not connected are responsible for occurring problems when converting loads.

In the Total Moment to Origin dialog section, the determined member loads are compared with the applied area loads. If there are differences, you can use the button to open the initial dialog box once more. Specifications must be adjusted in the Settings for Load Generation dialog box (see Figure 11.178) that you can access by using the button.

The two buttons in the info window have the following functions:

Table 11.15 Buttons in info window for converted member loads

The Convert Area Loads to Member Loads dialog box where you can adjust the generation parameters opens again.

The work window opens where you can change the view (view mode). To return to the Info window, use [Back] or [Esc].