We've done it - with at least with stringers. Although most of the trusses I've worked on did not make the stringers composite for various reasons. Waaaaaaaay back we had a client that was opposed to all composite design. In another case the panel lengths weren't that long that studs would make a difference.

As far as floor beams go, I think it's more economical and easier for erection to run the stringers over the floorbeams.  

Yes, composite trusses have been in use since the 1960s especially for deck trusses.

As to high trusses, this has little effect on the overall truss behavior.  

Pony trusses and deck trusses this is probably very helpful.

Regards,
Qshake

Eng-Tips Forums:Real Solutions for Real Problems Really Quick.
 

I've done it for a thru truss.  We had I shaped bottom chords and made them composite with the concrete deck as well which eliminated the out-of-plane floor beam bending issue.  

Thanks all for the input.  I just received a set of plans that has exactly what I was asking about as well.  The concept seemed practical, I had just never seen one before.  Also, was composite design being used that far back for trusses?  A lot of span bridges built around that time around here weren't designed to be composite.  It probably depends on which region one is in but we seem to be behind everyone.

Composite decks make sense structurally...but I wouldn't use that system in cold areas where lots of salt is used.  Replacing a deck is one thing, replacing a composite deck is another.