Problem due to instability

[Engineer3636]

Hi,

I have the attached structure which I am trying to analyse as simple bar model. I am getting instabilty errors of type 1 and 2. I can not see the reason why.

see below link.

I have also taken the same file and reduced the model by deleting the 2 bays on the left hand side and it only throws up 2 errors. Please also see attached.

Can someone please help me and tell me how to resolve this issue.

The link for the models is

https://www.wetransfer.com/downloads/254de92e44cb1618012c1f638f08a1db20140325143401/3eefae8d519f6df1...

Thanks

Daniel

[Artur.Kosakowski]

You either need to add RY supports (see the attached picture) or remove RY release from the Screw 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.

[Engineer3636]

Artur, thanks for your quick reply.

Yea, this is the only way I can remove errors but if I put a support Ry at the ends of the 50x50 boxes - in reality (ie on site) do I have to provide a support here?

Regards

Daniel

[Artur.Kosakowski]

In reality there has to be something that prevents rotation of these beams along their own axes e.g. the fact that they lay on something 

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.

[Engineer3636]

See attached connection between 50x50 and 100x50. It sits directly againsteach other. I assume this is what you mean?

I assume there is no other way to model this?

Thanks again.

Daniel

[Engineer3636]

[Artur.Kosakowski]

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.

[Engineer3636]

Ok, Artur.

There will be some rotation but it will be minimum. How do you do elastic support or release you mention. and how do you calculate what value to put in to say how fixed it is?

Thanks

Daniel

[Artur.Kosakowski]

Just enter the value for RY on the elastic tab of either support or release definition dialog. What value to enter is going to be your decision. I would start with fully fixed rotation and check the values of MY to see if there is any significant bending there.

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.

[Engineer3636]

I have restraint 1 end of all the 50x50 boxes and looking at the reactions I have no values. To me this means that I dont need a bracket and the bending is insignificant. Can you have a quick check to see if my assumption is right. I have also attached the section and plan of the parts I am trying to analyse.

This is very much appreciated and the service provided by yourself and autodesk is very good for new users.

https://www.wetransfer.com/downloads/d7b39d7bee9839090654618a80abce4b20140326084403/382411

Regards

Daniel

[Artur.Kosakowski · Accepted solution]

There is no value of MY bending in the additional supports you created therefore there is no rotation of the HSS sections. In other words these supports help in avoiding the instabilities but don't influence the results.

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.