The “Load Distribution Area” represents the most general method to apply loads on beam elements by creating a structural area with particular properties to distribute free loads.
Based on a defined influence area a routine calculates the forces and bending moments of the related support lines and beam elements. Those results are saved in the database permanently.
By applying a load to the “Load Distribution Area” the program performs the following steps:
- Converting the applied load dependent on the load distribution area mesh into nodal loads.
- Converting the nodal loads into support and beam loads.
All available free loads can be allocated to the “Load Distribution Area”.
- Point Loads
- Line Loads
- Area Loads
- Volume Loads
The “Load Distribution Area” Dialogue Box
The necessary input to define the “Load Distribution Area” is compact but effective. Actually, only three options are available.
It isn’t actually necessary to enter a number each time creating a new “Load Distribution Area”, as the software will increase it automatically. However, referring a free load to a “Load Distribution Area” requires selecting it by its number afterwards.
The input defines the range to consider adjacent elements. It points in the positive and the negative direction perpendicular to the area.
- Affected Group
To consider all groups within the range is the default. The “All” input is only available in the first drop-down. However, the two other drop-down menus include a “NONE” input instead. Selecting up to 3 groups is possible.
Let’s see how the command works on a quick example. Let’s apply a snow load on a roof truss. The picture below shows the roof truss with the mandatory members. The different colours already represent the different structural element groups.
- Roof batten – Group 1
- Rafters – Group 2 (odd numbers)
- Rafters – Group 3 (even numbers)
- Ridge Perlin – Group 4 (not further considered in this example)
The position of the “Load Distribution Area” should set to the centre line of the roof batten.
1 Create a Load Distribution Area for Rafters (Group 2+3) only
To consider group 2+3 only set the inputs of the “Load Distribution Area” dialogue box when creating the “Load Distribution Area”. So the position of the area is at the centre line of the roof batten – don’t forget to enter the depth to include the rafters too.
Watch the video below to learn how to create a “Load Distribution Area”.
2 Assign an Area Load to the Load Distribution Area
Define the snow load as free area load. Within the “Free Area Load” dialogue box set all properties as usual. When selecting the type of the load keep in mind you are going to assign it to a “Load Distribution Area” which comes with a separate local coordinate system. For the snow load choose “PZZ – load global Z”.
To refer to the “Load Distribution Area” select the Option “Load Distribution Area LAR” in the Drop-down menu Reference. Now select the number of the “Load Distribution Area” in the drop-down menu Numbers/Groups. You should have similar settings as in the dialogue box below.
3 Check the distributed Loads in WINGRAF
Check the distributed loads in Wingraf to ensure you did the correct setup but also to see the load values generated automatically.
Within Wingraf and in the sidebar to the left activate the first tab “Structure values, loads, results”. Open the section “Loads” – “Loads related to elements” – “Beam Loads”.
In the second tab “Load/Design cases” select the load case of the free area load from before. In my example, it was load case “3 – Snow”.
By simply changing the properties of the “Load Distribution Area” you can load the roof batten only. Just select group 1 (roof button) instead of group 2+3.
You just learned about how to successfully create a “Load Distribution Area” and assigned a “Free Area Load” to it.
Find further information in the SOFiLOAD User manual in chapter 3.16 LAR – Load Distribution Areas.
Download the “Load Distribution Area” example and practice the workflow.
The “Load Distribution Area” command is a useful feature to put loads on grid systems such as roofs and facades. The selection of directions for loads is enormous and covers all possibilities.
Software version: SOFiSTiK FEA v2018-08.