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Rationalizing composite slab penetrations

Rationalizing composite slab penetrations

Rationalizing composite slab penetrations

(OP)
Let's say I have a partially composite slab (6" slab/2" deck) system which the contractor would like to turn into swiss cheese (ok that might be a slight exaggeration, but they would like to install a number of ~8" dia holes). My latest rationalization has been to reduce the effective flange width locally by utilizing a deeper section of the slab (depths of the compression block for the composite section are typically less than 3/4" for the affected beams). As long as I am not changing the net effective area of concrete available for compression, the net section properties should remain relatively unchanged (technically, the d distance for the compression block is reduced, but initial thoughts are that this is relatively insignificant for the affected sections). This way, I can keep the holes closer to the desired location and keep the architect happy (or maybe the interior designer is running the show now). Thoughts? What am I missing?

RE: Rationalizing composite slab penetrations

I buy it for the concrete. Identical logic is used all the time with CIP slab openings. Usually, the bigger issue is the local loss of the decking as tensile reinforcement.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

RE: Rationalizing composite slab penetrations

I had a webinar on this. a couple of methods were presented, but the only one I really remember is from the attached article. You wander the slab width around openings, and check the slab for the induced moment.

http://msc.aisc.org/globalassets/modern-steel/arch...

RE: Rationalizing composite slab penetrations

Please disregard my previous post. I was thinking of the capacity of the slab deck to span perpendicular to the beams whereas I'm now fairly sure that you're interested in the composite design of the beams themselves. StructSU10's excellent aticle is a good deal more thorough than anything I would have come up with. It would be interesting to see your opening layout to see if it warrants a detailed analysis or if some judgement can be applied to further simplify the problem. An 8" hole is pretty minor but, then, a forest of them in close proximity is another matter.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

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