Composite Steel Beam 1

[LPPE]

If you have a beam with concrete slab, metal deck, shear studs, you find your effective flange widht from the provisions in Chapter I (ASD). Suppose you have a slab penetration opening (for mechanical ducts, what have you) somewhere in your effective flange. Is there any provision that says if you dont have a homogenous effective flange across the whole beam, you cant use composite design? All I see is in the commentary about "trenches" and it says use the smallest effective flange width at the "trench".
Example: Suppose I have a mechanical opening at mid span of the composite beam that occurs to one side of the beam center line. Can I still design the beam as composite using the effective flange width at that point (like a composite spandrel beam)??

 

[JAE]

What we do is use the composite properties of the "spandrel" beam when there is an opening along one side. Thus, we ignore the portions of the slab that do occur on the same side of the beam as the opening.

So if I had a beam, spanning 20 feet, with a 5'x5' opening along one side at midspan, I would design the entire 20 foot beam assuming composite slab occurring on one side only and ignore the 7.5' and 7.5' of slab that does exist on the other side on either end of the beam. This is simply a conservative approach that underestimates your beam stiffness.