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Re: Concrete Flat Slab Hole

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Dear Richard,

Its hard to give you advice without looking at the plans, but the way
you describe what you are doing, you are simply adding a new huge
column.  The column is the width and lenth of an elevator. ( The
bearing Cmu wall around the shaft. I imagine this will reduce most of
the spans.  I suppose you may have cracking in the slab after you cut
your hole since you may not have top steel in that region.

Just think of it as adding a big column to the mix and calculate the
change in demand because of the change in spans.  If the existing
steel is adequate your done.
Expect some cracking because of the new bearing points.

Ken Tarlow

---Richard Lewis <rlewis(--nospam--at)> wrote:
> I have been asked to analyze a flat slab with drop panels for a
client.  The
> flat slab was designed in 1955 and is a typical two way slab with
> strips and middle strips.  The client wants to cut a hole in the
slab for an
> elevator, as close to one of the columns as possible.  This will
> loosing about 1/2 of a column strip.  I do not have much experience
with flat
> slab two way construction.  I want some guidance form some of the
> engineers what I should research, study, look for, brush up on, etc.
as I
> begin to tackle this problem.
> The elevator shaft can be constructed from CMU block and be load
bearing so I
> can put the load from the cut column strip into the shaft.  I assume
> will help the shear problem since it will not add shear to any other
> around the column.  I still want to stay a reasonable distance from
> column.  I know I need to check bending since what was a continuous
span will
> now have a simple support at on end.
> Any helpful insight would be greatly appreciated.
> __________________________________________________
> Richard Lewis, P.E.
> Missionary TECH Team
> rlewis(--nospam--at)
> The service mission like-minded Christian organizations
> may turn to for technical assistance and know-how.

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