How to add cladding weight on modal analysis

[benas.kaulius]

Hi everyone,

I'm trying to do modal analysis with my bridge model, to see the difference of increasing deck weight and natural frequencies. So as a deck I'm using cladding and to weight to the deck I've created another Load Case with dead load to whole cladding. So, to make cladding not weightless I've chosen to do "modal analysis taking into account static forces" (Added photo of the settings and bridge model). Everything seems to be working, but I can't choose the option to only count active mass direction to Z axis. How can I make my modal analysis only to Z axis and make cladding not weightless too?

[Rafacascudo · Accepted solution]

Claddings have no stiffness ,they only distribute the loads.

You should not use in a modal analysis.

Use a FE meshed slab instead.

[okapawal · Accepted solution]

Hi @benas.kaulius 

"modal analysis taking into account static forces" is meant for non-linear models.  There is no need to use it on a slab, and you are not able to choose active direction.

You should use a panel with thickness, and set the panel calculation model to distribute the self-weight load to members.

If you really want to neglect FE stiffness, you may use a cladding and then convert to masses the load case with uniform self-weight.

[benas.kaulius]

So I should change my structure type to "Building design"?

[okapawal]

Use "Shell  design"