Compact section question 3

[71corvette]

I've got a question regarding compact section criteria as outlined in the AISC Steel Design Manual, 9th edition.

Table B5.1 - "Limiting Width-Thickness Rations for Compression Elements" lists limiting width-thickness ratios for compact and non-compact sections based on an elements width-thickness ratio b/t.

However, in the "Dimensions and Properties" section located at the front of the manual they have several columns of "Compact Section Criteria" listed, one of which is b/2t.

My question is, what is the difference between these? Why does B5.1 call out b/t while the "Dimension and Properties" tables use b/2t?

I'm guessing i'll kick myself when I read the answer, but the reason is escaping me at the moment.

Thanks,
Tim

 

[haynewp]

b/2t is to account for the "b" being the entire width of the flange, the buckling element is the 1/2 the flange protruding from the web. See note a on page 5-35.

 

[Lion06]

haynewp is right. Read the definition of "b" in the table that you are referencing. It is not the full flange width. It is 1/2 the flange width.

 

[frv]

The 13th Edition includes illustrations to make this clear.

 

[Bagman2524]

b is the distance of the part from the stiffened edge. Thus for W's & WT's its' 1/2 of bf, for L's its' bf.