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Re: Minimum RC column dimension, rebars

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I don't see any exception to UBC 1921.4.1.1 for seismic induced forces.  You really have to use 12" min. dimension. Now if the factored axial load is less than 0.10Ag*f'c then the member becomes a flexural member. In this case you are bound to follow UBC 1921.3.1.4 which permits minimum width of 10".
Column is defined as a member with a ratio of height to least lateral dimension of 3 or greater and primarily to support axial compressive load. So it does not mean that when the member is vertical it is called a column. The load define the member if it as column or a beam. A beam might be horizontal but if it is subjected primarily to axial compression then it becomes a column and vice versa. Therefore a member subjected to less than .10Ag*f'c is considered to be a flexural member or beam.
I don't see any provision that limits stirrups and ties to at least 3/8" dia.  The only requirement per UBC 1903.5.1 is that reinforcement shall be deformed bars. I remember from the table of an old book by Harry Parker that #2 rebar comes in plain bars only. This is the reason why most people use #3 (3/8" dia.). So in my opinion if #2 is already available in deformed bars then we can use that too. Anyway, the lesser the area the closer the spacing is.
Hope this will help you.
Alfonso S. Quilala Jr., P.E.  

----- Original Message ----
From: Alex C. Nacionales <anacionales(--nospam--at)>
To: seaint(--nospam--at)
Sent: Friday, September 14, 2007 8:14:05 AM
Subject: Minimum RC column dimension, rebars

For earthquake resistant structures, RC columns are limited
to a minimum dimension of 12 in. or 305mm. , UBC 1997 1921.4.1.1 .  and a minimum steel ratio of .01
For two story residential buildings with column spacing of
4.0 meters or less and height less than 7.5 meters , this  results to columns with strengths in excess of what is needed to carry the required loads.
Is there any exception to this code provision that will allow an 8" or 10" RC column.?
If the factored axial load is less than 0.10Ag*Fc' will this permit me to use a 10" RC column.?
Where can I find the the code that limits stirrups and ties
to at least 3/8" ~(10mm) Dia.
Thanks in Advance.
Alex Nacionales, C.E.

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