Offset function in Robot

[pascal.bogdan]

Hello,

I'm doing some tests about offset function in comparison with ETABS. I created a simple model in ETABS and the same one in Robot and I have compared the results.
So:
- the structure without offset in both programs gives almost the same results, as you can see in the first picture that I have attached .
- when I use the offset function in Robot I get some strange small values in comparison to the initial results from the structure without offsets. Also there is a big difference between Etabs and Robot now.

I have attached the two files (robot and etabs ones) and I hope that someone from Autodesk will be kind to give me an answer. If I didn't done something correct in those models please let me know.

Thank you in advance!

[Rafacascudo]

I see there´s a slab on robot model. Is there a slab also in Etabs?
In Robot ,if you use the beam offset to put the slab on top of the beams , it will appear a normal force in the slab and also in the beam .The reduced moment you find in the beam compared to the structure without offsets is normal and I think is correct.

Rafael

[smm.144]

By offset, do you mean "Assign>frame/line>End (length) offset" in Etabs?

[pascal.bogdan]

I see there´s a slab on robot model. Is there a slab also in Etabs?
In Robot ,if you use the beam offset to put the slab on top of the beams , it will appear a normal force in the slab and also in the beam .The reduced moment you find in the beam compared to the structure without offsets is normal and I think is correct.

Rafael

Yes, there is a slab in Etabs. I tried to make those two models as alike as much so that the results to be correct. Look first at the results from both structures without any offsets and you will see almost the same results.

[Rafacascudo]

I saw your pics and dloaded your robot model. I don´t have Etabs.
What I meant is that the results have to be different.The beam is connected to the slab .It functions as a L-beam or T-beam.You can check that ,due to the increased rigidity, the beam deflections are considerably smaller compared to the structure without offsets.

There´s no difference in the etabs results between with and without offsets models?

[Gazes]

I am simply quoting Wacek Reczek (who temporarily lost access):
________________.
Nothing suspicious in the Robot example (I have no ETABS).
If you position the beam using offsets you transform section having 2 “overlapping” rectangles into “T section”.
A short manual calculations for a T section having flanges of 3xbeam width transforms “initial forces” My=135, N=13
(arising from the model without offsets) into internal forces for “offseted beam” equal My=53, N=640.
This is not exactly which Robot displays (71/512 as far I remember) but it is in reasonable range
(different section stiffness has to influence on slightly different forces distribution).
What is suspicious it is lack of the “real” changes in the ETAB file. Unfortunately I cannot help in this
________________.
Wacek Reczek

[smm.144]

Yes, there is a slab in Etabs. I tried to make those two models as alike as much so that the results to be correct. Look first at the results from both structures without any offsets and you will see almost the same results.

Can you tell us how you applied offset in Robot step by step?

[smm.144]

I think you are misunderstanding the functionality of End offset in Etabs. I don't think there is any similar option in robot...