Diaphragm in ETABS

[compe_ad]

Hi all! Is it essential to define diaphragm in my model? How does ETABS apply auto seismic load (from ASCE) if diaphragm is not defined? I know it is a simple question to be asked but can you please provide me your insights?

 

[CuriousBearcat]

Diaphragms work as one of the horizontal seismic force transfer mechanisms in a structure. So if you building has diaphragms it is essential to model it but if not, it is not required. The eccentricity only applies for rigid diaphragms (torsional effects) - so if you have a flexible diaphragm, you can select "Semi-Rigid" from SAP2000 auto-seismic loads and override "e" eccentricity as 0 in the lateral load options. This is what I do - but curious to know what others think too.

-Just a curious engineer

 

[Luceid]

You could test it out with a simple one-bay-four-column model, define your levels, copy the same structure at each level and run an auto seismic case, see what it does. Does it apply at each level? I'm sure ETABS' lateral load manual probably has some guidance on this too