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Re: Web-Buckling of Concrete

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>From: Rafael Sabelli <Sabelli(--nospam--at)>
>To: "'SEAINT'" <seaint(--nospam--at)>
>Subject: Web-Buckling of Concrete
>Date: Fri, 23 Oct 1998 16:25:07 -0700
>Dear Structural Engineers:
>I am investigating using a slab-on-grade to transfer
>seismic shear.  The segement in question is 32' long
>and would transfer 15 klf from one grade beam to
>another which is 20' over.  My questions are:
>1.  Is there a limitation to the depth-to-thickness ratio
>beyond which the shear strength calculated using ACI
>318-95 section 21.6.5 cannot be achieved because of
>web buckling?  This would be analogous to AISC LRFD
>(1st Edition) section F2.2, which gives reduced shear
>capacities for very slender webs.
>2.  If buckling were allowed to occur, could the ACI values
>be achieved by activating the diagonal tension field?
>This would be analogous to AISC LRFD Appendix G.
>I would appreciate references and opinions on this subject.
>Thank you,
>Rafael Sabelli
I believe there is no lateral unstability if the unbraced length of a 
concrete beam is less than b x 50.  

IE: a 12" wide beam will not have lateral buckling problems if its 
unbraced length is equal to or less than 50 feet.

I believe that information is somewhere in the ACI code. Perhaps in the 

Jose Diez PE


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