Greentram Software Support Forums  

Go Back   Greentram Software Support Forums > SuperBeam > Support

Support Technical and other questions related to the use of SuperBeam

Reply
 
Thread Tools Display Modes
Old 16th July 2008, 04:54 PM   #1
shove2001
Member
 
Join Date: Jul 2008
Posts: 7
Default Beams failing in LTB (Buckling)

Hi,

I have had a checking engineer claim that beams designed using SuperBeam are failing in buckling. I am investigating which beams (of four) and re-printing "with Details" shown to show the Buckling checks shown. Has anybody else had similar claims?

Mark
shove2001 is offline   Reply With Quote
Old 16th July 2008, 06:41 PM   #2
Tony Bryer
Administrator
 
Join Date: Apr 2008
Location: Melbourne, Australia
Posts: 829
Default Re: Beams failing in LTB (Buckling)

I would like to know more on this. Is he suggesting that the calculation is wrong, or does he think that you have used the wrong effective length? Recent discussions in the Structural Engineer suggest that checking engineers do not always agree on what effective length factor should be used.
__________________
Tony Bryer, Greentram Software Pty Ltd
Tony Bryer is offline   Reply With Quote
Old 17th July 2008, 07:30 AM   #3
shove2001
Member
 
Join Date: Jul 2008
Posts: 7
Default Re: Beams failing in LTB (Buckling)

I will check this effective length issue and get back to you.

Mark
shove2001 is offline   Reply With Quote
Old 18th July 2008, 08:47 AM   #4
shove2001
Member
 
Join Date: Jul 2008
Posts: 7
Default Re: Beams failing in LTB (Buckling)

The Building Inspector has changed his tune and does not have a problem with Superbeam. He now says that my loads should be increased...

" For steel beams, BS 5950 requires the loadings to be factored (ie increased) by a factor of; -Dead loads x 1.4 -Live loads x 1.6. This gives a factor of safety overall of +50% ."

Only when he adds this 50% do the beams fail in buckling. Is this factoring taken into account in Superbeams section selection?

Mark
shove2001 is offline   Reply With Quote
Old 18th July 2008, 09:14 AM   #5
Tony Bryer
Administrator
 
Join Date: Apr 2008
Location: Melbourne, Australia
Posts: 829
Default Re: Beams failing in LTB (Buckling)

It looks like the BCO has failed to realise that SuperBeam calculations are done using BS449 which is a permissible stress code (BS5950 is a limit state code). You do not factor the loads when using a permissible stress code - the factor of safety comes from the fact that the permissible stress shown (e.g. 180N/mm2 for a restrained S275 steel beam) is well below that which will cause failure. If you were doing the calculations to BS5950 then you would need to factor the loads by 1.4/1.6 but the resulting stresses would then be compared against the actual strength of the material (275N/mm2 for S275 steel).

For a discussion on the use of BS449 see our web page http://www.sda.co.uk/info/sbw/bs449.htm
__________________
Tony Bryer, Greentram Software Pty Ltd
Tony Bryer is offline   Reply With Quote
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is Off
HTML code is Off



All times are GMT. The time now is 10:16 AM.


Powered by vBulletin® Version 3.8.5
Copyright ©2000 - 2018, Jelsoft Enterprises Ltd.
Copyright 2011 Greentram Software Pty Ltd, Melbourne, Australia