Mass Summary by Story is not the same as Mass Summary by Diaphragm ETABS 2016

[Tomaz888]

Hello everyone.
Can anyone explain what could be the reason for differences in values of Mass Summary by Story and Mass Summary by Diaphragm. I use ETABS 2016. I have a simple building, all the shells are divided with the intersections of visible grids. I have a friend who has the same problems. I know the solutions would inserting point mass but that is very time consuming.

Thank you very much Tomaz

 

[Agent666]

You don't have some of the 'mass' defined as part of the diaphragm (either by points or via shell). Try reselect every floor and reapply the diaphragm. Lumping lateral mass at storey level may affect it, have not tested this though.