https://communities.bentley.com/products/ram-staad/f/ram-staad-forum/208636/ram-structural-system--semirigid-diaphragm-with-untopped-metal-deckI am currently working on a model with concrete tilt walls and joist girder moment frames (using the virtual joist tables) with an untopped metal deck as my diaphragm. Based on articles I have found on this site (as well as classifications per ASCE7)en-USTelligent Community 12https://communities.bentley.com/thread/629966?ContentTypeID=1Tue, 19 Jan 2021 22:21:49 GMT6dad98f5-dbc9-4c4d-a9ba-e9da8dc6aa8e:09c97142-1bda-41b6-806e-8018a6270ae9Seth Guthrie<p>It really is an engineering judgment call on how stiff the diaphragm should be. The type of deck, the welding, and overlap all have some impact. The only general advice would be to run it with a range of stiffness assumptions, i.e. two times to capture the worst case for each frame. Or you can make it flexible and assign loads to each frame that are conservative.&nbsp;</p><div style="clear:both;"></div>