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...
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 =...