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Width/Thickness Ratios

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If you designed for A36 steel, then your design should be good for steel of 
higher strength.  I don't think that when you designed the section, you 
worried about whether the yield strength of the A36 steel supplied was 36 
ksi, 40 ksi, or 50 ksi, did you?

Limiting the stress to limits for lower strength steels will not affect 
instability of higher strength steels.


A. Roger Turk, P.E.(Structural)
Tucson, Arizona

Dan Goodrich wrote:

. > UBC 2211.8.4.b requires that beams and columns in special moment 
. > frames have a b/t ratio less than 52/sqrt(fy).  I have a beam that was
. > designed with A36 steel which meets this requirement.  The supplier
. > substituted A572 steel which does not meet the requirement.  

. > What's the background on this requirement?
. > If the frame is significantly stronger than strength levels require 
. > because of drift limitations, would it be okay to not meet the 
. > requirement?

. > b/t = 8.1  
. > 52/sqrt(fy) = 7.35

. > TIA.
. > Dan Goodrich, P.E.