Reaction forces at supports

Hi all,

Similar problem to my previous post - here now I have a block of random beams in a cube shape. I want to do some basic compression of this cube and look at the reaction forces.

I have applied a displacement support to the top nodes of the structure, and a fixed support to the bottom. However, the reaction forces at these supports are difficult to understand. You'd expect the reaction forces to mostly be in the negative z-direction on the bottom, but they're in the y-direction.

Changing the plane used in the support components doesn't really do what I expect either - any ideas?

Thanks for your help.

Best,
Umar

Attachments:

FEAofLatticeSpecimens.gh, 1.9 MB
RandomBlock.PNG, 256 KB

Replies to This Discussion

Permalink Reply by Karamba3D on July 4, 2017 at 5:53am

Dear Umar,

your prescribed displacement is in global Y-direction. This is why the main reaction force is also in Y-direction.

Best,

Clemens

Permalink Reply by Umar Hossain on July 4, 2017 at 6:10am

D'oh!

Thanks again Clemens!

Permalink Reply by Umar Hossain on July 7, 2017 at 7:29am

I have one other question though - regardless of the input force, why is it that in my definition the sum of the reaction forces isn't zero? There are only two supports being applied, and no external load. Surely the reaction forces on the top and bottom should sum to zero? Wouldn't that imply rigid body motion otherwise?

Permalink Reply by Karamba3D on July 11, 2017 at 12:54pm

You are right, the sum of reactions must be zero.

In your definition there are duplicate supports defined on some nodes. In Karamba 1.2.2 this is not checked and causes the wrong result. I will add a corresponding error message in the next release. In the meantime use the 'Remove Duplicate Points'-component to remove duplicate supports in order to arrive at the correct result (see attached definition).

Attachments: