This load assistant facilitates the task of assigning an area load to members of the model. This allows you, for example, to apply a snow load to the rafters of a roof plane or a traffic load to a grillage, without having to determine the load shares of the members manually.
Basis
The Basis tab manages the load parameters.
Generate in Load Case
Select the load case from the list to which the loads are to be assigned. Using the
button, you can create a new load case.
Categories
Load Distribution
The list offers various options for how the area load acts:
- Uniform: The load has a constant magnitude.
- Linear: The load is distributed with a linear variation. In the 'Area Load Parameters' section, you can specify three reference nodes with the corresponding load magnitudes.
- Variable in X / Y / Z: The load is distributed with a linear variation in the direction of a global axis. You can define the area load parameters in a separate tab (see section Variable).
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 custom 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 true area (like a dead load) or the projected area (like 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 the numbers of three nodes with the assigned loads here. Using the
button, you can also select the nodes graphically in the work window.
Options
If you activate the 'Ignore New Members' check box, the area load acts only on the currently existing members of the area load plane according to the definition in the 'Geometry' tab. Members that you add later in the area load plane will not receive any shares of the area load.
With the 'Smooth Point Load' check box, 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 check box is not activated (default setting), the eccentrically arranged members are normally considered when determining the load shares. If you activate the check box, these members will not receive any shares from the area load.
With the 'Consider Cross-Section Distribution' check box, you can control whether the area load also acts on the inclined members resulting from a haunch definition (default setting). If you activate the check box, the area load is not applied to members in the load plane that have an irregular cross-section variation (see chapter Cross-Section ).
Geometry
In the Geometry tab, you can define the boundaries of the load plane and specify the load-bearing members.
Defining 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. To do so, use the
button. The plane is highlighted in the selection color. With the
button, you can also select the cells of a plane that RSTAB automatically detects in the model.
At least three nodes are required for a plane. The area does not need to be bounded by members on all sides.
You can define various area load planes, which will 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 using a template member 'parallel' to all unloaded members. The
button allows you to transfer the members from Object Selections. To do so, select the relevant object selection (OS) in a separate dialog.
Settings
The 'Load Application Area' controls how the area load acts in the model:
- Completely Filled Plane: If there is an area between the members that is not represented in the RSTAB 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 structural framework.
- Not Filled, Only at Members: 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.
Variable
The Variable tab is available if you selected a variable load distribution in the 'Basis' tab that acts in the direction of a global axis.
Here, you can define a freely varying load such as a height-dependent wind load. Specify ordinates or the 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 Plane' Type
Using the list, define whether the permissible deviation of a member from the load plane should be described '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 tolerance and generates the corresponding loads.
Tolerances for the 'Node on Line' Type
In the list, you can select whether the permissible deviation of a node from the member definition line should be described 'Absolute by a Distance' or 'Relative by an Angle'. Then enter the distance Δs or angle φs.
Display Member Loads and Distribution Areas
As soon as 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 so, use the Show Separately entry in the context menu of the area load or activate the Loads → Load Assistants → Member Loads from Area Load → Show Separately option in the navigator - Display. Furthermore, with the navigator option Show Distribution Areas, you can display the Voronoi cells of the selected load.
