ROBOT VS ETABS why have the DIFFRENCE

[Anonymous]

I set up two models which are etabs and robot. When set both model suport are pinned. the reaction of support is very small different around about 0.01

But when i set support is fixed , the models reaction have a big difference.

why have the  DIFFRENCE ? how can handle it 

please help me 

[mustafahesenow]

Hi @Anonymous

These changes because the bending stiffness of the columns in both of Etabs and RSA are not equal.

Please check the material properties of Etabs and RSA . Should be same material exactly and same modifier if applied.

From your model :

As you noticed :

The total moment on the structure :

3*(10*9+10*6+10*3)=540KN.m

When you set the supports pinned : means that no base bending stiffness so the moment will be distributed Geometrically  as coupled forces on the columns and the reaction on the columns will be 540/(3*2)= +- 90 KN.

When you set the support as fixed : The moment will be distributed Geometrically plus moment on the supports coming from the stiffness of the columns :

If you can notice that from attached picture of your model :

Sum of moment value =192.86 Kn.m

Sum of reactions and forces =540 Kn.m 

This is came from the coupled forced Fz + Sum of moment value 

57.86*2*3+192.86=540.02 KN.m = Sum of reactions 

Etabs model shows that the coupled Fz reactions are smaller than RSA model means that the bending stiffness of the columns in Etabs are bigger than RSA which that means the E modulus on Etabs is bigger than RSA .

[Artur.Kosakowski]

Hi @Anonymous

Without having the chance to investigate both models it is hard to tell. You may want to look at the material properties and displacements too. Perhaps you could try to compare a simple frame with the point load applies in its top corner acting in the frame plane first.

[Anonymous]

how can i upload the etabs model to the page?

[Anonymous]

this is the etabs model and robot model

https://drive.google.com/drive/folders/1QB5VZHQsXKOf2csQDWWQqAPFFSIozLkN?usp=sharing

[Artur.Kosakowski]

Hi @Anonymous

Please be informed that I will not be able to open and investigate your ETABS model. This has to be done by some nice person having this program available for him/her.

[saclovitzky]

Its much better to attached ETABS file as .e2k txt file  , so, any version can open it.

[Anonymous]

uploaded https://drive.google.com/drive/folders/1QB5VZHQsXKOf2csQDWWQqAPFFSIozLkN?usp=sharing

[saclovitzky]

Pls. see attached the difference is really negligible.

[saclovitzky]

Hello,

I cannot open your txt file(try opening it with ETABS 2013 NL) but I modelled it again in ETABS, see my previous response, the difference is less than 2%.

Even, if you modelled it with identical material properties/support condition etc, numerical difference will surely emerge(but most of them are negligible and also refer to mustafa's reply).

[Anonymous]

can you  share your model to me ?

i also have a concern about the code of the model use 

i can not find the same code which in etabs and robot 

can you show me your setting about the model

[saclovitzky]

Regardless of the code, just model it(ETABS) the same way that you model it in Robot. And you will notice that the difference is neglible.

Try modelling first a simple 2D structure and compared its results. This is the only way to investgate and it is up to you, if you want to create a more complex structures and compare the results between the 2 softwares.  This is one way of building up your confidence in using "any" softwares.

[Anonymous]

i mean the code of practice 

[mustafahesenow]

I had mentioned to you if the materials and sections are the same in both of Etabs and Robot 

The results will be very closed 

[Anonymous]

i know it but i can not find one same material 

can you share your setting

[mustafahesenow]

Hi @Anonymous

You dont know How to apply same material in both of Robot and Etabs ?

So for what this comparison? 

[Anonymous]

Good morning sir 

i try to use the almost code of practice in etabs and robot

but still have some propriety can not match

shear module can not change 

[mustafahesenow · Accepted solution]

1

[Anonymous]

i try make the propriety  same

but the result still have difference

the Fx and Fy almost same

but the Fz still have a large different

[saclovitzky]

Can you  attached again your e2k file?