Slender web in I beam E7-16

[gjsimms]

I have looked but cannot find any definitive answers to queries on calc of Qa. This earlier thread references the matter;

thread507-130866

For the case of an I beam with compact flanges but slender web the calculation of Aeff/A, where A= total section area, seems only to make sense if Aeff = Aflange1 + Aflange2 + effective web area.
The AISC definition of Aeff implies (to me) that it comprises only those elements for which be is calculated, i.e. stiffened elements which for an I shape would only be the web, in which case Qa could be a small number (Aeff(web only)/A) which would have a disproportionate effect if the flanges were large.
Can anyone clarify this?

thanks

Graham

 

[ishvaaag]

I am not presently very up to date with the AISC code as I was around year 2000 (I live in Spain). Anyway I look to AISC 360-10 and when dealing with the axial capacity in compression of one member seems to give a reasonable quotient for Qa=Ae/Ag, where Ag is the groos area and Ae

summation of the effective areas of the cross section based on the reduced effective width, be, in^2 (mm^2)

Other thing is by the specifics of the connection you may get some further reduced capacity.

I am not entirely sure if I understand your question, please clarify if not.

 

[gjsimms]

Ooops, don't know what happened to the reference, it is supposed to by one from ChiChuck on 4 Aug 2005; eng-tips.com/ viewthread.cfm?qid=130886 (thread172-130886)

ishvaaag, it is the philosphy of what constitutes 'the summation of effective areas...based on effective width, be ...' that I find vague as 'be' only applies to stiffened elements (in E7).

 

[ishvaaag]

OK, maybe then somewhere or someone should make clear that the compact flanges or anything under some flange slenderness is fully effective; but my understanding is that such is the intent. Will look about it and if found will post.

 

[firai]

A_eff is determined as the sum of the gross unstiffened element areas and the reduced stiffened element areas. For an I beam, the calculation is exactly as you described in the initial post. I don't have the manual/spec on hand to cite any references, but you can also confirm this with the examples CD that comes with the manual. Good luck!

New York, NY

 

[gjsimms]

Many thanks