topic Re: support uplift in Robot Structural Analysis Forum

support uplift

saclovitzky — Tue, 11 Sep 2018 09:16:53 GMT

Hello,

Pls. see attached file. I am just wondering why I have an uplift on props nos. 6 & 8? It is only carrying SW of the slab?

Any help will be greatly appreciated.

Re: support uplift

Artur.Kosakowski — Tue, 11 Sep 2018 09:25:03 GMT

Hi @saclovitzky

The first thing is to look at the deformation:

This is why the load takedown approach is not applicable for a models with more complex static schemes.

If I managed to answer your question(s) press the Accept as Solution button please. This will help other users to find solution(s) much faster. Thank you.

Re: support uplift

saclovitzky — Tue, 11 Sep 2018 10:55:47 GMT

@Artur.Kosakowski

What do you mean Artur?So literally there's no uplift?The reason why I model this, is to actually see what actual loadings will go for the middle props(as only 2 props are allowed!)

Re: support uplift

Artur.Kosakowski — Tue, 11 Sep 2018 11:01:33 GMT

HI @saclovitzky

I don't understand what you mean. My point was that if you would calculate reactions (forces in the columns) based on the tributary area you would see no uplift which exists in reality.

Re: support uplift

saclovitzky — Tue, 11 Sep 2018 11:32:05 GMT

Thanks Artur for your reply. Taking the weight by tributary area is the simplest way to get the reactions in every floor level(just multiply it by 5 , but I am getting huge loads and 2 props are not enough). What I am trying to do is to model the whole lot and see what actual load these 2 middle props are getting(capacity per prop =73 kN). In so doing, I didnt realize that the other 2 props are getting uplift. If I isolate a single level of slab there's no uplift but you need to multiply it by five to get the total reactions, and the loads on the middle props will exceed its capacity. I am just wondering whether I represent the model of props correctly(ie, I mean do I need releases on their connection?)

Re: support uplift

Artur.Kosakowski — Tue, 11 Sep 2018 12:29:00 GMT

Hi @saclovitzky

The use of releases depends on the connection type. If they don't transfer bending you should define them.

Re: support uplift

saclovitzky — Tue, 11 Sep 2018 12:42:56 GMT

@Artur.Kosakowski how can I model the props(column) just for axial loads only(is this the "pinned-pinned" releases?)

Re: support uplift

saclovitzky — Tue, 11 Sep 2018 13:05:05 GMT

@Artur.Kosakowski

Is there any chance that I can remove the uplift on the said props. Is there any "releasing" connection technique that can eliminate this uplift?

Re: support uplift

Artur.Kosakowski — Tue, 11 Sep 2018 13:11:53 GMT

Hi @saclovitzky

You can define them as compression only bars.

If I managed to answer your question(s) press the Accept as Solution button please. This will help other users to find solution(s) much faster. Thank you.

Re: support uplift

saclovitzky — Tue, 11 Sep 2018 15:33:54 GMT

Thanks Artur but why it takes so long to converge?

Re: support uplift

Simau — Tue, 11 Sep 2018 16:51:36 GMT

@saclovitzky

To avoid upfilt, you can add linear release from either sides of the central beam.

Before doing that you have to create 2 pannels by story.

Re: support uplift

Artur.Kosakowski — Wed, 12 Sep 2018 08:09:12 GMT

HI @saclovitzky

This is due to the fact that Robot has to determine which of the compression only bars are active (under compression) and which should be switched off (when in tension) with each load increment which requires calculations of the whole model at each of the iteration.

If I managed to answer your question(s) press the Accept as Solution button please. This will help other users to find solution(s) much faster. Thank you.