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Re: 8" Columns

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Also, do not forget the fireproofing issue.  An 8" column, even if allowed by the ACI code, may not satisfy the fire code (depending on your jurisdiction and version of the code).  My office uses 12" as the smallest column dimension from both a practical standpoint and a fireproofing standpoint.

Daniel

----- Original Message ----
From: "Gerard Madden, SE" <gmse4603(--nospam--at)gmail.com>
To: seaint(--nospam--at)seaint.org
Sent: Friday, October 5, 2007 8:21:58 PM
Subject: Re: 8" Columns

But it's higher E doesn't offset the geometric reductions in I, S, Z, r, J, etc...and would not be as strong as a 3000psi 12"x12" for most failure modes except possible pure axial compression (depending on the unbraced length) and shear.

f`c has very little to do with capacity for flexure or beam-column elements when even a slight eccentric axial load is applied. Slenderness governs most capacity checks in column design.

Why not use a TS filled or encased in concrete instead?

Also, but the time you radius the ties and clear cover requirements, the bars are so close together your d is virtually nothing.

-g

On 10/5/07, Alex C. Nacionales <anacionales(--nospam--at)insightts.net> wrote:
David,

    8"x8" RC columns with Fc'=10000psi has more
compressive strength than a 3000 psi 12"x12" column.
The 8" column would be more expensive i am sure but Architects sometimes
limits dimesions for aesthetic reasons.

Alex C. Nacionales


----- Original Message -----
From: "David Fisher" <dfisher(--nospam--at)fpse.com>
To: < seaint(--nospam--at)seaint.org>
Sent: Saturday, October 06, 2007 1:22 AM
Subject: RE: 8" Columns


> 8" - 2*1.5" (cover) - 2* 0.375" (ties) = 4 1/4"
>
> Not much section left!
>
> I've seen 8" sonotubes under a porch, but thats it.
>
>
>
> David L. Fisher SE PE
> Senior Director
>
> Cape Cod Grand Cayman Holdings Ltd. - Cayman
> Fisher+Partners Structural Engineers Ltd. - Cayman
> 372 West Ontario Chicago 60610
> 75 Fort Street Georgetown Grand Cayman BWI
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>
> -----Original Message-----
> From: refugio rochin [mailto: fugeeo(--nospam--at)gmail.com]
> Sent: Friday, October 05, 2007 12:21 PM
> To: seaint(--nospam--at)seaint.org
> Subject: Re: 8" Columns
>
> That is not true.  ACI 21.3.1.4 allows for a width of 10" for Flexural
> members of special moment frames.
> ACI 21.11 for Frame Members not proportioned to resist forces induced
> by earthquake motions, does not place any restrictions on the minimum
> dimensions.
>
> I am mainly wondering how most people approach the design of such a
> member that has to accept seismic displacements?  Is there any
> research in the realm of 8" concrete members undergoing design
> displacements, and their strength capacities?  I do not want to design
> such a member and have it bust due to seismic loads and lose vertical
> strength capacity...
>
> -RR
>
> 2007/10/5, Gerard Madden, SE <gmse4603(--nospam--at)gmail.com>:
>> 12" is the minimum dimension for a concrete structural member other than
>> walls and slabs.
>>
>> -g
>>
>>
>> On 10/5/07, refugio rochin < fugeeo(--nospam--at)gmail.com> wrote:
>> >
>> > I think I should explain a bit more...  8" Concrete Column.  The
>> > column should be able to take the lateral deformation imposed by the
>> > overall structure though, which is generally attached to a rigid
>> > diaphragm ...
>> >
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>> -gm
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--
-gm