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Re: AISC LRFD- composite beams

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marfra(--nospam--at) wrote:
> I find it strange that most texts including the Salmon & Johnson advise
> that using steel beams composite with concrete slabs generate savings of
> 20% to 30%.
> The design charts and calcs indicate a considerably higher saving
> particularly when beams under 16" are used with slabs 5" and over.This
> is quite common for most buildings under 4 stories high. Deflections
> usually are also fine.
> A typical W10X15 has an permissible Mn of 43 kip ft . When composite
> with a 5" slab the permissible is generally over 75 kip ft. Im I doing
> something wrong
> Mark Francois

This is where LRFD shines, but be warned.  Vibration can be a serious
concern with these lighter sections.  Refer to AISC publications for a
recommended procedure to check.  You might also try Vulcraft composite
joists, if you want a really light section.  If you can wait a day or
so, I will try and check the capacity you are mentioning.  A couple of

Beam spacing?
Stud height / diameter / quantity?
Steel grade?
Conc. Strength?
Deck orientation / properties?

There are pretty good tables in volume one for rough numbers, have you
tried those?

Jake Watson, E.I.T.
Salt Lake City, UT