Web Side Sway Buckling to BS EN 1993 (EC3)

[CJLCivilStruct]

Hello.

I have been assisting in the design of an unrestrained column section which is supported continuously on the bottom flange and subject to a point load (see sketch attached), and would like to calculate the design resistance of the web due to the transverse force.

Currently, I have found methods of calculating both web crippling and buckling when the flange is restrained on plan.. However, this is not the case in my scenario. Eurocode 3 only appears to cater for restrained beams as far as I can see with no implicit suggestion of how to account for the top flange being unrestrained. I tried increasing the effective length of the web within the EC3 formulae.. but when sense checking against BS5975 (Temp works code which has this exact scenario set out with reference to BS5950) the resistance values were very different (with BS5975 being 4x less!).

I'm going out on a limb and say I've either completely missed something, or this is not the first time someone has encountered this problem.. help would be very much appreciated! (also - i've searched Eng-tips but struggled to find reference to this particular problem)

 

[SWComposites]

sketch missing

 

[CJLCivilStruct]

Oops, classic... - hopefully see attached!!

 

[kieran1]

Steel blue book web buckling capacity tables?

Kieran

 

[CJLCivilStruct]

I believe the Bluebook would be for a restrained top web too - the resistance value for this case (150mm stiff length bearing >Clim from end with 254UC107).

However, using the allowable stress methods in BS 5975 using Table J.1 of Appendix A for the increased effective length (hopefully embedded below) results in a resistance of around 250kN.

I fully expected there to be a difference as EC3 is limit state design and BS5975 is allowable stress design, but i'd have thought they'd be a lot closer?