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Diaphragms Assignment - Split or Together?

Diaphragms Assignment - Split or Together?

Diaphragms Assignment - Split or Together?

(OP)
So part of my structure have level without floor and there is no diaphragm assigned since I assigning diaphragm from shell. But without the diaphragm, wind load is not applied. I understand that using the same diaphragm means the joints will have an effect on one another. However, these vertical element shouldn't have an effect since there is no diaphragm effect without slab. I read somewhere that it is okay to assign the same diaphragm since the column is continuous, is this correct?

Does it matter if I use the same diaphragm or different diaphragm for each section of the structure? I am trying to assign diaphragm for the structure with the layout as follows. I can easily identify four groups that are connected by corridors, not sure if I should further separate the lower block into more groups. I tried both and it seems that the forces will just redistribute differently and it is not clear which is the better model. Also my storey shear changes for lateral load which I assume is due to the diaphragm extent having a different shape. Any comments?


RE: Diaphragms Assignment - Split or Together?

Doesn't ETABs have a semi-rigid diaphragm? You can then use a semi-rigid diaphragm, but make it pretty flexible / weak. You load would then get distributed based essentially on tributary area of each lateral force resisting frame.

RE: Diaphragms Assignment - Split or Together?

You can split up diaphragms as long as you’ve got your full wind area covered. Just know that your wind is going to get applied individually to each diaphragm, which may not be appropriate. Personally I’d assign the same semi rigid diaphragm to everything in your screenshot.

At least under US codes you’d be pretty unlikely to meet the requirements for rigid diaphragm assumptions with that floor plate anyways. Just need to make sure the stiffnesses of your floors are modeled realistically.

Really tough to tell scale from the screenshot, but if it’s a fairly large floor plate then expansion joints and/or pour strips may be appropriate to incorporate as well.

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