Critical moment

[HenkaCarlsson]

I have studied the critical moment that Robot uses a little deeper and I need an explanation to the attached simple example:

A beam with 4 supports gets a much lower Mcr when it's connected over the middle supports than it has when its released over the supports.

I checked it with another program that calculates Mcr (LTBeam) and with LTBeam the Mcr is about 10% higher when the beams are connected

[Artur.Kosakowski]

I have made a quick hand calcs for  a similar beams and I can't see any problem with values in Robot.

Please in case you have some doubts about the numbers try to do the same yourself first. I'm not able to do this for every post on the forum.

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.

[Anonymous]

Maybe this could help. It says that 2 methods give similar results.

[HenkaCarlsson · Accepted solution]

Thanks for the help.

The problem for me was that I didn't have access to ENV 1993-1-1 only to EN 1993-1-1 where the method of calculating Mcr that Robot uses no longer is described. But thanks to Участник I was able to find the document SN003 where it is described also.

So now I could calculate it and understand the way Robot calculates Mcr. The result from my calculation with this method was the same as Robots value of Mcr.

Maybe it could be nice to have the possibility to give the value of Mcr to Robot if you have used some other program or method to calculate it?

Regards Henrik C

[Artur.Kosakowski]

This proposal has been added to the wish list.

[Artur.Kosakowski]

Maybe it could be nice to have the possibility to give the value of Mcr to Robot if you have used some other program or method to calculate it?

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.

[HenkaCarlsson]

Yes Thank you! 🙂

And I hope that you continue the work to improve the automatic calculation of Mcr so the user option won´t be necessary in the future versions.

/Henrik

[kmmdD66ZQ]

@Artur.Kosakowski  what you are showing is that the program is implying here that it is better to have a simply supported beam than having a continues beam. I have to say that this is incorrect.

If you are looking into the norm that you have posted in another  forum (Link below) and look up the values in the curves of this norm you will find that a continues beam is better than a simply supported one.

I have to say that AutoDesk need to look into and improve the way the program calculates Mcr, because that simply looking up values in a predefined table is not accurate enough and it can give some very wrong results.

i.e. the example you have shown the Mcr of the beam is a lot higher than calculated by Robot for a continues beam.

Solved: Lateral buckling - critical moment - Autodesk Community - Robot Structural Analysis Products