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Re: Different concrete strengths for columns and floor system

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I wouldn't use 10.15 for the condition you describe.
Section 10.15 isn't a "carte blanche" for every
possible condition that can crop up. Another condition
where 10.15 does not apply is in post-tensioned
parking structures where you have floors at different
elevations (ramps) framing into interior columns. You
will often have a 10 foot high column that's comprised
of more beam concrete than column concrete (due to
beams framing to the column at staggered elevations).
Does this mean you can ignore the fact that most of
the column is of (possibly) strength beam concrete?
No. It is for this reason that we usually use the same
concrete in the columns as we do for the slabs in such
structures. You won't get any benefit in using higher
strength concrete in the columns if most of concrete
in the columns isn't the higher strength.

Also,... 9"x36" columns?! How are you going to get the
spandrel beam top and bottom bars through the column?
If you do get the bars through the column, how are you
going to get the concrete through the bars?

Let me guess - the architect really didn't want the
columns to be wider than 4"...

Cliff Schwinger

--- MAM <mam(--nospam--at)cyber.net.pk> wrote:
> Refer to ACI Code Section 10.15 for "Transmission of
> column loads
> through floor system" ,
> which says that where the column concrete strength
> does not exceed the
> floor concrete
> strength by more than 40 percent, no special
> precautions need be taken.
> Now, consider a case of  a mutistoried building
> periphery  column 9"x36"
> of  5000 psi
> concrete framed by  9"x48" deep spandrel beam of 
> 4000 psi  concrete,
> along the column length.
> The column upto the bottom of the beam is cast with
> 5000 psi concrete
> whereas the column portion cosisting of the 48" deep
> beam is cast with
> 4000 psi concrete, as is cutomary. Now my question
> is:
> Is it reasonable
> to apply  the above ACI clause to this situation and
> do nothing about
> the low concrete strength for the 48" portion of
> column, since
> the concrete strength
> ratio is  less than 1.4 ? Any comments would be
> welcome.
> MAM
> 
> 
> 
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