Ieff for composite steel beam 2

[Lion06]

Can someone point me to a reference on how to calculate Ieff for a partially composite steel beam? I can't find anything in S&J or online except for a reference to BS 5950-3).

 

[WillisV]

Ieff = 0.75Iequiv
Iequiv = Provided as equation C-I3-3 on p16.1-309 of 13th edition (incorrectly noted as Ieff).

 

[Lion06]

Thank!!! That is quite a little gem that was tucked away in the commentary.

 

[271828]

WillisV, I am not sure that's correct. What source did you use to decide that Iequiv is the quantity computed using Eq. C-I3-3?

For what it's worth, my mentor back in grad school is one of the big-name AISC guys and has been teaching steel for 40 years and he uses Eq. C-I3-3 in deflection calcs. Of course, that's the way I've been doing it for years too, but it's just because I followed his lead.

Also, to further muddy the water, Segui uses Ieff=0.75Itr in one of his example problems (Page 580 of the 4th Ed.).

 

[Lion06]

271828-

That note about Iequiv is in the errata (I did look for that myself).

I noticed RAM also uses Ieff=Iequiv, not 0.75Iequiv. Also, my S&J text talks about using 0.33 to 0.5Ec when determining Itr to account for concrete creep and shrinkage.

 

[271828]

OK, perhaps that's correct.

I think Segui's method is clearly not correct because it totally leaves out the effect of more or fewer studs. Even ILB in Table 3-20 varies depending on Sum(Qn).