2D frame to Eurocode - value of XLT

[Anonymous]

Hi,

I'm designing a portal frame to BE EN 1993-1. My rafters fail the global stability checks for buckling resistance and bending & axial compression. I think the problem is in the calculation of chi LT (XLT in robot). Robot gives me values of XLT=0.18, while my hand cals show XLT=0.975. I attach my full calcs note

Any ideas would be greatly appreciated. Thanks

[Romanich]

Hi @Anonymous ,

Could you please also attach your hand calculations?

[Anonymous]

Hi Romanich,

My calculated XLT was actually 0.952, but still much higher than the one calculated in robot. See attached

[Romanich]

Hi @Anonymous ,

Mcr and lateral buckling curve are different. Have you tried to input these values manually and check the results?

[Anonymous]

Thanks for your help @Romanich ,

Changing  the Mcr and buckling curve helped. My XLT is still different, but this must be due to  a different value of beta taken by Robot.

[Anonymous]

@Romanich ,

Just wondering why the Mcr wasn't calculated correctly? My portal frame is rather standard, so I'm surprised with the result.

Thanks, Magda

[Romanich]

Hi @Anonymous ,

Could you please attach your Robot model?

[Anonymous]

Hi@Romanich ,

Please see attached. This is the one with Mcr changed manually. Thanks

[Romanich]

Hi @Anonymous ,

Try to zip model first or check this topic

https://forums.autodesk.com/t5/robot-structural-analysis-forum/sending-bigger-files/td-p/3795062

[Anonymous]

@Romanich 

see below, thanks

https://wetransfer.com/downloads/9a7b981b75378b79bca37258a2dad88520190313120042/1aa9c4f5ab7dc88cc20c...

[Romanich]

Hi @Anonymous ,

Also I would kindly recommend to always check warnings:

[Anonymous]

Thanks @Romanich 

I'm still a bit confused with all the lengths that need to be specified (Ly; Lz; Lcr,y; Lcr,z; Lcr,low) and how they are taken into account in calculations. Are there any guidelines on how buckling calcs are dealt with in Robot?

I.e. I've changed  Lcr,low to =1.64m, beta to =0.75, lambda lt,0 to =0.4 as you suggested and I'm still getting different (than my hand calcs Mcr=1588) value for Mcr=4300.

Warnings were due to the haunch specified in the model, I have deleted it now.

[Romanich]

Hi @Anonymous ,

Please also check these topics:

https://forums.autodesk.com/t5/robot-structural-analysis-forum/purlins-design-lateral-buckling/m-p/3763998

https://forums.autodesk.com/t5/robot-structural-analysis-forum/lateral-buckling-critical-moment/m-p/3253094#M1701

[Anonymous]

Thanks for suggestions @Romanich