Composite Slab Penetrations

[jechols]

What is the largest slab penetration allowed without reducing the effective flange width in a composite slab? Does anyone know of any references that discuss in detail penetrations in composite slabs?

 

[jike]

I assume that you are talking about the opening cutting into the composite beam or girder effective slab flange width of a composite beam or girder.

I know of no guidelines other than performing the beam calculation with the reduced effective width and seeing how much that affects the stresses. Of course, near the end of the span there would be little affect, but you might want to adjust the location of your studs depending upon the exact situation.

 

[jechols]

Thanks for the input jike.

It just seems impossible to determine where every pipe or conduit will penetrate. I called AISC solutions center and they said to ignore holes that are 5" or less. For openings between 5" and 12" over cut the hole and place a steel sleeve or frame then grout back around the frame (or be in place before the slab pour) with material stronger than the concrete, then I would not have to reduce the effective flange width. Openings larger than 12" would require a reduction in the effective flange width. Does this seem reasonable?

Thanks
Jechols

 

[jike]

Jechols:

AISC recommendations sound reasonable to me.

Like many things in engineering, try to get a handle on how significant the problem actually is.

For instance, say your full effective width is 84" and you have (two) 8" diameter holes at one particular cross section. The effective width at that cross section has been reduced to 68". I would not be too concerned if the concrete stress with the full cross section (84") is 1200 psi actual vs. allowable of 0.45 x 4000 = 1800 psi because 84/68 x 1200 = 1482 psi which is still less than 1800 psi.

I hope this helps.