This load wizard simplifies the task of applying an area load to the members of the model. This allows you, for example, to apply a snow load to the rafters of a roof plane or a live load to a grillage beam without having to determine the load portions of the members manually.
Base
The Base tab manages the load parameters.
Generate in load case
Select the load case in the list to which the loads are to be assigned. With the
button, you can create a new load case.
Categories
Load distribution
The list offers various options for how the area load acts:
- Uniform: A load of constant magnitude is applied.
- Linear: The load is distributed with linear variation. In the 'Area load parameters' section, you can specify three reference nodes with the corresponding load magnitudes.
- Varying in X / Y / Z: The load is distributed with linear variation in the direction of a global axis. You can define the area load parameters in a separate tab (see section Varying).
Coordinate system
The area load can act perpendicular to the load plane ('local z') or with reference to the global XYZ coordinate system. Alternatively, you can select or create a user-defined coordinate system.
Load direction
If the area load does not act perpendicular to the load plane, but in the direction of a global axis, the list offers various selection options.
The area load can be based on the actual area (as a dead load) or the projected area (as a snow load). The load direction is illustrated in the dialog sketch.
Area load parameters
Enter the magnitude of the uniform area load. If the load varies linearly, you can define here the numbers of three nodes with the assigned loads. With the
button, the nodes can also be selected graphically in the work window.
Options
If you check the 'Ignore new members' box, the area load acts only on the currently existing members of the area load plane according to the definition in the 'Geometries' tab. Members that you add later to the area load plane do not receive any portions of the area load.
With the 'Smooth point load' checkbox, you can smooth point loads that may occur in complex geometries during load distribution. The point loads are then distributed to the adjacent members.
The 'Consider member eccentricity' option controls how the area load acts on the members of the plane with Member Eccentricities: If the checkbox is not selected (default setting), the eccentrically arranged members are regularly considered when determining the load portions. If you check the box, these members do not receive any portions of the area load.
With the 'Consider cross-section distribution' checkbox, you can control whether the area load also acts on the inclined members resulting from a haunch definition (default setting). If you activate the checkbox, the area load is not applied to members in the load plane that have a non-uniform cross-section variation (see chapter Cross-section ).
Geometries
In the Geometries tab, you can define the load plane boundary and specify the load-bearing members.
Boundary of the area load plane
Define the boundary of the area load plane by clicking the corner nodes of the plane one after another in the work window. Use the
button for this purpose. The plane is marked in the selection color. With the
button, you can also select the cells of a plane that RFEM automatically recognizes in the model.
At least three nodes are required for a plane. The area does not have to be bounded on all sides by lines or members. Planes with curved members, however, are not suitable for generating member loads.
You can define various area load planes, which then appear line by line in the table.
No effect on
This section allows you to exclude members such as bracings or purlins from load transfer. You can define the members graphically with the
button, either individually or via a pattern member 'parallel' to all load-free members. With the
button, you can transfer the members from Object Selections. To do this, select the relevant object selection (OS) in a separate dialog.
Settings
The 'Load application range' controls how the area load acts in the model:
- Fully filled plane: If there is an area between the members that is not represented in the model, the area load of the entire plane is distributed to the members. This allows you, for example, to apply roof or wall loads to a framework.
- Not filled, members only: If the model consists only of members, such as a lattice tower, the load acts only on the member cross-sections. The load is determined taking the member position into account.
Varying
The Varying tab is available if you selected a varying load distribution in the 'Base' tab that acts in the direction of a global axis.
Here, you can define a freely varying load, such as a wind load depending on height. Enter ordinates or relative distances and assign the corresponding load values.
Tolerances
In the Tolerances tab, you can influence the criteria according to which members and nodes are assessed as belonging to a plane or line.
Tolerances for the 'Members in the plane' type
Using the list, specify whether the permissible deviation of a member from the load plane is to be described as 'Absolute by a distance' or 'Relative by an angle'. Then enter the distance Δz or angle φz. The load generator detects cells for all members within this limit and generates the corresponding loads.
Tolerances for the 'Nodes on the line' type
In the list, you can select whether the permissible deviation of a node from the member definition line is to be described as 'Absolute by a distance' or 'Relative by an angle'. Then enter the distance Δs or angle φs.
Display member loads and distribution surfaces
Once the member loads have been generated, you can display the applied load not only as an area load, but also as actual member loads. To do this, use the Show separately entry in the context menu of the area load or activate the Loads → Load Wizards → Member Loads from Area Load → Show separately option in the Navigator - Display. Furthermore, with the Navigator option Show distribution surfaces, you can display the Voronoi cells of the selected load.
