Roof diaphragm

Hello,

You can model the deck as plate element and apply loading as plate pressure on it. Make sure to mesh the plates to establish beam -plate connectivity which in turn will allow the loads to be trasferred from deck/plates to beams. This way you can take care of actual stiffness and loading for the sloped roof.

Thank you for your response. What do you mean by mesh the plate to establish beam-plate connectivity. Is this different from the regular meshing?

This is a snapshot of my model. The beams in the sloped area are 9.4m long and spaced at 2m. So I will have a plate of 9.4m by 2m meshed into smaller plates. Is this what you mean? 

Thank you for your response. What do you mean by mesh the plate to establish beam-plate connectivity. Is this different from the regular meshing?

This is a snapshot of my model. The beams in the sloped area are 9.4m long and spaced at 2m. So I will have a plate of 9.4m by 2m meshed into smaller plates. Is this what you mean? 

Hi John,

Your understanding is correct. Actually when we model beam and plates together in a file and load is applied on the plates, that loads gets transferred to the beams/columns through only nodes. So, if you model a plate of size 9.4m x 2m, the loads will go directly to the columns and the beams will not experience any force due to those loads. In order to pass the loads through beams, you need to mesh the plate in smaller sizes so that the loads from the plate goes directly to beam first and then transferred to column- which is the intended load path.

Thanks again for you response. I have a follow up question.

When plates are modelled alongside beams, the plates are connected to the center of the beams. Is there a need to offset the plates up so they are attached to the top flange of the beam (when viewed in 3d) as will be the case when steel decks are attached to roof beams in reality?

Thanks.