I have a Validation > Model > Loads > “Decomposition to multiple diaphragms” warning. Why do I get this and how do I resolve it?

Question

I have a Validation > Model > Loads > “Decomposition to multiple diaphragms” warning. Why do I get this and how do I resolve it?

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Answer

A Decomposition to multiple diaphragms validation warning occurs when more than one diaphragm is identified on the same level and the second smaller diaphragm is greater than 5% of the wind profile width.

The tooltip indicates this to you when you hover over Decomposition to multiple diaphragms or any problem simple wind load item listed within the branch.

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You can double click the Decomposition to multiple diaphragms or individual simple wind load to locate it in the active scene view. If the item is not in the active scene view then the Structural 3D view is opened and set active.

To clarify what the statement means we will consider Wind in X and Y in conjunction with the explanations below.

Wind in X direction

The wind profile width is 4m. Level 1 has two separate diaphragms - one behind the other. The second diaphragm has a width of 100% of the wind profile width. This is greater than 5% and hence the validation warning is provided.

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Wind in Y direction

The wind profile width is 24m. Level 1 has two separate diaphragms - side by side. The smaller second diaphragm has a width of 25% of the wind profile width. This is greater than 5% and hence the validation warning is provided.

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The method of applying wind load using the simple wind load command to diaphragms is discussed in detail in the Tekla Structural Designer product guides. It is imperative that you refer to this to understand the limitations of the method when you have disconnected diaphragms.

So, the above explains why you get the warning, what about how to resolve it?

We will look at the two scenarios identified above:

Wind in X = Wind load parallel to disconnected diaphragms

If the second diaphragm is behind the first when resisting simple wind load then the applied loads are shared between both diaphragms. The diaphragm locations are beyond the scope of the intended use of the Simple wind load command and as detailed in the Help system it is recommended that you manually input the loads instead of using the simple wind command.

Note, however, that it is possible to apply manual loads in conjunction with the simple wind load command to obtain your final applied loads. To resolve, you could manually apply panel in-plane point loads to correct the loading. In the screenshot below the incorrectly applied 9kN load to the second diaphragm is applied in the opposite direction to cancel it and is applied to the first diaphragm location to increase the load at this location.

Note. Manually applying loads to modify the simple wind load distribution will not remove the validation warning. This will only disappear if the simple wind load command is not used in this direction and the load applied manually.

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Wind in Y = Wind load perpendicular to disconnected diaphragms

If the diaphragms are side by side when resisting simple wind load then you could redefine the simple wind load so that separate simple wind loads are applied to each diaphragm. In this way only one diaphragm acts with the wind profile width. Since a second diaphragm does not exist within each individual wind profile width the warning does not appear.

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