topic Re: Strange axial force in end wall rafter in Robot Structural Analysis Forum

Strange axial force in end wall rafter

Anonymous — Tue, 07 Nov 2017 05:56:26 GMT

Hello!

I get high axial forces in end wall rafter when using FE mesh. But by claddings the axial force is gone. The rafter is pinned between column.

The strange thing here is that it is not the wind that is generating the axial force. It is the snow and self weigth load.

any idea where the forces orgin is?

Model:

Warehouse with 1/40 roof angle

Truss span

Pinned column

X-bracing to pick up the lateral wind force.

Re: Strange axial force in end wall rafter

Artur.Kosakowski — Tue, 07 Nov 2017 08:19:04 GMT

Hi @Anonymous

I'd check the deformation and focus on how the meshed wall influences what happens with the rafter.

If you find your post answered press the Accept as Solution button please. This will help other users to find solutions much faster. Thank you.

Re: Strange axial force in end wall rafter

Anonymous — Sat, 11 Nov 2017 09:58:27 GMT

Hi Artur

Sorry for the late reply.

i made a new model with only claddings. And it seems okay now. I think it might have been the mix of claddings and roof, that cause the problem.

What would you recommend, use claddings for the whole structure, or walls and roofs as a FE-mesh? Im only interested in the frame.

Re: Strange axial force in end wall rafter

Artur.Kosakowski — Mon, 13 Nov 2017 08:29:57 GMT

Hi @Anonymous

Mind that cladding do not provide any stiffness to a structure so if walls are intended to limit horizontal displacements then they should be meshed panels.The same allies to slabs but you can also use diaphragms instead of meshed panels.

If you find your post answered press the Accept as Solution button please. This will help other users to find solutions much faster. Thank you.

Re: Strange axial force in end wall rafter

Artur.Kosakowski — Wed, 15 Nov 2017 12:46:54 GMT

Hi @Anonymous

I just wanted to ask if you still need any additional help for your model?

Re: Strange axial force in end wall rafter

Anonymous — Sun, 19 Nov 2017 20:41:45 GMT

Hi Artur

And thanks for the help!

I modeled the roof using rigid link (semi rigid- one way). But get a high moment in the connection from the column to the truss. it is supposed to be pinned. And since the roof is ridgid this might not work?

The real case, is a pinned structure with metal deck (acts as a stiff plate) and the lateral forces is picked up by the wind bracing.

Is there some way to configure the connection? Or do i need to use floor/FE mesh

Thank you! 🙂

Re: Strange axial force in end wall rafter

Artur.Kosakowski — Mon, 20 Nov 2017 09:35:01 GMT

Hi @Anonymous

Have you tried to define a release at the top of the column?

If you find your post answered press the Accept as Solution button please. This will help other users to find solutions much faster. Thank you.