Error in panel's load distribution on beams

[Anonymous]

Hello RSA community,

I've been facing a problem with my panels recently especially for load distribution on beams. When distributing the loads manually on beams i get the expected moment diagram figuring in the attached picture 1. On the other hand when using a solid homogeneous slab with a shell calculation model, i get the faulty moment diagram figuring in picture 2. All the beams in my design are affected by this problem.
More over, some of the moment diagrams look edgy  

(note that there's no problem with the meshing it is refined to element size 0.5).

Could anyone please help out?

Please find attached picture 1 and 2, as well as the model in question.

Thanks

[Anonymous]

Hi,

the slab has is stiffness and is connected to the node as well as the beam. This means that even if you give the beam a release, the slab modelled as fixed won't allow the beam to rotate. So obviously it reaches M = 0 in the node, but then you have a negative moment due to the fixed connection created by the slab. 

[Anonymous]

Helo,

So according to your expertise the loads are well distributed and the moment diagrams either for the beam of the slab are correct?

When reducing the stiffness of the slab i get better moment diagrams on beams with higher moment values however reducing the stiffness of the slab affects the deflection which gives false results.

Thank you for your time.

[Anonymous]

Hi,

I just had a look to the "shape" of the moment of the concrete frame.

I personally won't set a pinned connection in a concrete frame as I think is not easy to create in a concrete frame.

There are some ways to do it, but I don't think is your case.

[Artur.Kosakowski]

Hi @Anonymous

 some of the moment diagrams look edgy  


This is due to the different shape functions of bar and surface elements. The values in given node along a beam should be averaged.

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.

[Anonymous]

Hello,
Could you please be clear about averaging the values in given node along a beam?
Thank you for your support
Regards.

[Artur.Kosakowski · Accepted solution]

Hi Johnny,

Something like this:

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.