The different assigning load area Uniform (shell) and uniform to frame (shell) SAP2000

[wisnu666]

guys, i have a question. i still dont know what is the different between assign load area in uniform (shell) and uniform to frame (shell). can you guys explain me the different? maybe in value? or can you guys tell me about the concept of loading uniform (shell) and uniform to frame (Shell)

thanks in advance

 

[darkjmf1]

Uniform load in a shell shall direct load to the joints of the shell, independent of the frames the shell is supported on.
Uniform to frame load shall direct load to those frames intersecting the shell. It is useful for loading frames without having to calculate their tributary areas. You can use dummy shells ("None" section) for that as well.
I hope it helps you to understand the difference.

 

[wisnu666]

thanks darkjmf1 for your explanation. but i confuse when i show the frame moment with uniform load. is that moment is a result from tributary load when assign the area load with uniform load, or it just the moment of frame itself? (moment from their weight self)

beside that it shows, the slab moment with uniform to frame loading give me the less value of slab moment compared to uniform shell loading assign. is that true?

 

[darkjmf1]

It also depends on the meshing of the shells and the frames.
If the joints of the shell are along the frame and not exclusively at the ends, then uniform load shall produce moments at the frame, as the intermediate joints shall introduce loads along the frame.
Of course, if self-weigth is activated, frames shall always show moment due to this load, independent of the other considerations.

You should also take into account that if shells are connected by means of intermediate joints to the frames, they shall work as a composite section (beam+slab) and therefore moments at frames and shells are not equal to those expected as independent elements.
If you just want to analyze the frames, use uniform to frame load with "None" shells, as they are dummy objects (neither rigidity, nor weight) that shall have no effect on the frame except transmitting load.

Anyway you can make easy manual calculations of the expected moments in order to check which load is being considered in any case.

 

[wisnu666]

or, if i want to calculate the frame moment that support a slab, i just use uniform to frame as loading assign?

so i conclude, to know the slab moment, just use uniform (shell) load assign. if i want to know frame moment thar support a slab i just use uniform to frame (shell) load assign?

is my conclution true?

 

[darkjmf1]

Not at all. With both type of loads you can know the moment at the shell and at the frame.
Only that you have to be consistent with the type of model you make (intermediate joints, rigidity of the shells, etc.) and be consequent with the results.

Typically, if shell is not important for you and you are just interested in frames, use "None" shells, without intermediate joints and uniform to frame loads.
A real application could be, e.g., a checkered plate supported on steel beams, where you do not really want to check the plate itself and you can neglect its contribution to the moment resistance of the beams.

On the opposite, you can find situations where you cannot ignore the shell.
For example, a concrete slab supported on concrete beams. In this case I would use shells with real rigidities, with a proper mesh so there would be (many) intermediate joints along the frames. In this case uniform load is the type of load to use. The moment at the beams and the slab is the one from a composite (beam+slab) section.

Of course there are many other intermediate situations where you should choose any possible combination of parameters...

 

[wisnu666]

ohhh i see i understand. thankyou for your explanation darkjmf1. thanks a lot. this is for my undergraduate thesis, to compare slab moment by using code and finite element analysis. really helpful with your concept explanation.

btw, one more question, since i modelled my beam and slab as concrete, and using loading uniform (shell) then i mesh my slab and my beam, is that true that the moment on beam is a moment from the beam weight it self, and tributary load from the slab?

 

[darkjmf1]

Well, it should be as long as you have self-weight activated.

 

[wisnu666]

thankyou so much darkjmf1!! hopefully we can discuss more about something like this. really helpfull!