elastic critical moment 1

[boki565]

Hey guys!
I cant figure why is Mcr in SCI P397 "elastic design of single span steel portal frame buildings Eurocode 3" calculated as Mcr = (C^2)*Cm*Mcr0 as you can see on picture below

And why is it calculated in SCI P363 "blue book" diferently as you can see on picture below

 

[Agent666]

The derivation in P397 explicitly accounts for the height difference between the shear centre and the point of restraint which is important for buckling, and it also directly allows for the possibility of a non-uniform section via the c parameter. I believe it's just a more accurate way of accounting the the restraints and effect on the buckling moment.

Take a look at the figure C.3 and how section C2.2 calculates the critical buckling moment and you will note a few more terms regarding the height of restraints relative to the shear centre. If you look in Eurocode 3 appendix BB.3.3 you'll see the same equations as P397.

Otherwise they are essentially doing the same thing, but I'd imagine the P397 equation is simply a bit more refined if you be bothered going to the additional calculation effort involved.

https://engineervsheep.com

 

[boki565]

Thank you for your information!