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Re: Different concrete strengths for columns and floor system

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No, it would not be appropriate.  The 1.4 allowance is based on transmission
through a floor slab where the depth is not only limited but effectively
confined by the slab.

Let's say you are working with an 11 foot floor to floor height, and a 12
inch slab, you still have 3 feet of a 10 foot clear height unconfined on one
side by floor system that is lower strength concrete.  You might as well ask
if the top third of a 9" wall can be 4000, yet you still want to design the
wall as 5000.  In my opinion this simply is not valid.

Paul Feather PE, SE
pfeather(--nospam--at)SE-Solutions.net
www.SE-Solutions.net
----- Original Message ----- 
From: "MAM" <mam(--nospam--at)cyber.net.pk>
To: <seaint(--nospam--at)seaint.org>
Sent: Friday, May 07, 2004 10:29 AM
Subject: Different concrete strengths for columns and floor system


> 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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