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Reciprocal frame on Robot

17 REPLIES 17
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Message 1 of 18
robmirgga
1401 Views, 17 Replies

Reciprocal frame on Robot

Hello all

 

I am hoping to analyse a reciprocal frame with stick elements (timber beams) mutually supporting each other in a loop.These beams are simply supported at the lower end and “rest” on the next beam all round in a circle (I have attached a photo of a typical reciprocal frame to clarify)

 

Unfortunately my model is made up of "chunky elements" and “thining them down” doesnt allow to keep overall geometry.

 reciprocal 3.pngstick elements not intersecting.JPGconnections using rigid links.JPG

In the robot model called reciprocal 3D I have tried by “bending” beams to fit geometry  while in “structure” I have “played” with the connection to work at offset (this doesnt not work though)

 

I have also attached a flat analysis model in “reciprocal”

 

Maybe I should be modelling beams as 3D elements? (I have tried this but results are more complex to check!)

 

I was wondering whether there was an option in Robot which allowed to insert pinned connections at an offset / distance? Maybe I am looking at this in the wrong software?

 

Thanks

17 REPLIES 17
Message 2 of 18

Try the following approach:

1. Model the beams as they are in reality (a bar in Robot being the center line of a real beam)

2. Connect 'bottom' and 'top' beams with rigid links defining the master node at the bottom beam and the slave with released rotations at the top one.

 

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.



Artur Kosakowski
Message 3 of 18

Thanks Arthur

 

So these rigid links would in effect be "offset" pinned joints?

 

 

Message 4 of 18

They should work like that.

 

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.



Artur Kosakowski
Message 5 of 18

Thanks for your help.

I will try this out and post reply later today or next week.

Regards

Message 6 of 18

When you release rotations for rigid links you should not define bar releases at the same locations. Delete the releases in the model you sent me and you should be fine.

 

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.



Artur Kosakowski
Message 7 of 18
robmirgga
in reply to: robmirgga

Fixed!

Thanks for your help!

Roberto

Message 8 of 18

I am working on a similar structure (see screenshots below) and have read a couple of research papers which suggest that if the top of the members are suitably tied with rigid connections then no lateral thrust should occur at the base. I have therefore modeled roller supports at the base of the rafters but am getting some instabilities and large lateral deflections. Presumably this is to do with the way the top connections / rigid links have been modeled? 

 

Untitled.pngUntitled2.pngUntitled3.png

Message 9 of 18

can you send the model?



Rafael Medeiros
Robot Structural Analysis

Message 10 of 18

Please see model file attached.

 

Many thanks

 

Daniel

Message 11 of 18

Mathematically ,Robot doesn´t accept a 3d structure without horizontal supports even if there will be no horizontal reactions ,like in a lifting situation.

The workaround I use is to set very weak horizontal springs, Doing that you will get the results you expect

 

reciprocal.jpg



Rafael Medeiros
Robot Structural Analysis

Message 12 of 18

Fantastic! Many thanks for your help.

Message 13 of 18

Hi @daniel.hubbard

 

Do you mind marking Rafael's post as the solution so that it is easier to find? Thank you.

 

 



Artur Kosakowski
Message 14 of 18

Of course. How do I mark it as the solution?

 

Best regards

 

Dan

Message 15 of 18

Hi @daniel.hubbard

 

You should be able to press such named button

 

accept as solution2.PNG

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.



Artur Kosakowski
Message 16 of 18

I do not have an accept as solution button visible. Perhaps because I commented on an existing thread which has already been marked as solved? 

Message 17 of 18

Hi @daniel.hubbard

 

I don't think it is related. I will mark the solution on your behalf and at the same time I'll ask the Forum Team if they are able to find out why you can't see it. 



Artur Kosakowski
Message 18 of 18

Hi @daniel.hubbard

 

Indeed your assumption was correct. You can't see the button as you are not the person who started this topic. I could move your post and the its answers to a new topic and then you would be able to do this but as your question IMHO is very much in the line with the original topic I'd rather leave it as it it is with the solution marked by myself. 



Artur Kosakowski

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