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cfarmer (Structural) (OP)
30 Jan 04 11:27
Looking for a good reference with guidlines or design procedures on analyzing existing structural slabs to accomodate new openings?
In my case I am looking at a 5 1/2" continous one-way slab spanning about 12'-0 clear between adjacent concrete beam supports with #3 bars @ 8" o.c. T&B with #3bars at 10" o.c.temperature steel in opposite direction. The proposed openings are 12"x16" (2 of these openings about 2'-0" apart). I can orient the opening so the 12" dimension is perpendicular to the one-way span of the slab.
I have not dealt much with new openings in an existing slab. Thanks in advance for any help
SperlingPE (Structural)
5 Feb 04 16:29
Some thoughts on openings in existing concrete slabs.  Once you cut the spanning steel, you have effectively made two simple spanning structures.  If new supports for the openings are installed in areas without openings, you have now made a multi-span structure.  Check the negative bending moments at the supports.
AlohaBob (Structural)
16 Feb 04 19:02
You have alot of capacity in that slab.

You really need more information though.

What strength is the bars? 40 or 60 ksi?

Are the bars properly placed in the slab for continuity?

It the slab to be cut an interior slab of a multispan or endspan?

Will you reinforce it?

Will you try to recapture the capacity that was destroyed by cutting the opening?

Do you know the concrete cover and it's strength?

Can you ensure you cut at most one effective bar?

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