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What is the difference between sub load cases and incompatible load groups?

Both sub load cases and incompatible load groups are used to define different cases of a certain load: for example wind blowing in different directions.

Let’s compare both (sub load cases and incompatible load groups) for a structure where you need to take 4 direction into account.

Using incompatible load groups

  1. Add four load groups for wind. Change the names to Wind 1Wind 2Wind 3 and Wind 4 to keep them apart.
  2. Indicate the load groups that cannot be present at the same time.
    • Click on the button Incompatible load groups
    • Select Wind 1 from the list and check the boxes in front of Wind 2, Wind 3 and Wind 4
    • Select Wind 2 from the list and check the boxes in front of Wind 1Wind 3 and Wind 4. 
    • Select Wind 3 from the list and check the boxes in front of Wind 1, Wind 2 and Wind 4.
    • Wind 4 is then automatically incompatible with Wind 1, Wind 2 and Wind 3 because of the previous selection.

Using sub load cases

  1. Add one load group for wind.
  2. Check the option Several load cases per group.
  3. Increase the number of load case to four. Diamonds will add Case 1, Case 2, Case 3 and Case 4 automatically to the list. You can change the name of the case if you’d like.
  4. The little guys define the incompatbility. When you click on the icon the little guys can hold hands or not.
    • if they are not holding hands, it means the sub load cases are incompatible. Meaning they cannot occur at the same time. This is particularly the case for wind/ snow loads.
    • if they are holding hands , it means all sub load cases will act on the structure at the same time. This is particularly the case for dead loads.

Pro’s and con’s of using either of these methods

Sub load cases Incompatible load cases
Easy to define and to modify Complex to define and to modify
List with load combinations is shorter. The different sub load cases are stored ‘behind the curtains’. It is easier for Diamonds to generate. List with load combinations is longer and harder for Diamonds to generate.
Only results for envelop
No results for each sub loadcase
Results for each load case and combination
Calculation time is more or less the same as with ‘Incompatible load cases’. Only pasting the results on the structure might go a little faster. But this difference is only noticible in larger structures. Calculation time is more or less the same as with ‘Sub load cases’. Only pasting the results on the structure might take a liggel more time then with ‘Sub load cases.

How to transform sub load cases to incompatible load cases

  1. Select the load groups with sub load cases and click on Ungroup load cases.
  2. The sub load cases are now ungrouped. Verify the incompatibilities using the button Incompatible load groups.

How to transform incompatible load cases to sub load cases

  1. Keep CTRL pressed in and select the load groups you want to combine.
  2. Click on ‘Combine load cases’.
  3. Verify the incompatibilities of the load groups.

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