## Limits for Reinforcement of compression members

## Limits for Reinforcement of compression members

(OP)

Hello all,

I'm looking for a clarification on the minimum reinforcement ratios for tied columns. I know ACI-05 10.9.1 states that the Ast for concomposite compression members shall be not less than 0.01Ag, then in the commentary I see it talks about the report of ACI committee 105 and a minimum reinforcement ratio of 0.005 was recomended for tied columns, then the next sentance says in all editions of the code since 1936 the minimum ratio has been 0.01.

Many of my co-workers say minimum area of steel for these members is 1/2 of 1% (0.005), but I'm just trying to find where in the code it states this and the above section is the only place I've seen this referanced, and from the wording of it it looks to me like the minimum is 0.01.

Any input would be appreciated!

Thanks.

I'm looking for a clarification on the minimum reinforcement ratios for tied columns. I know ACI-05 10.9.1 states that the Ast for concomposite compression members shall be not less than 0.01Ag, then in the commentary I see it talks about the report of ACI committee 105 and a minimum reinforcement ratio of 0.005 was recomended for tied columns, then the next sentance says in all editions of the code since 1936 the minimum ratio has been 0.01.

Many of my co-workers say minimum area of steel for these members is 1/2 of 1% (0.005), but I'm just trying to find where in the code it states this and the above section is the only place I've seen this referanced, and from the wording of it it looks to me like the minimum is 0.01.

Any input would be appreciated!

Thanks.

## RE: Limits for Reinforcement of compression members

## RE: Limits for Reinforcement of compression members

## RE: Limits for Reinforcement of compression members

## RE: Limits for Reinforcement of compression members

For example: if you have a 20 x 20 column and you think it's too large, you can design a column with half the area, Ag, still limited to 1% reinforcing.

20 x 20 = 400 sq. inches.

(min. steel typically = .01 x 400 = 4 sq. inches)

1/2 Ag = 200 sq. inches

sqrt(200) = 14.14 x 14.14 column.

At 1% steel this is 2.0 sq. inches

2.0 sq. inches is of course 0.005Ag of the original 20x20 column.

But you don't check a 20x20 column with 2.0 sq. inches. You must check a 14.14 x 14.14 column with 2.0 sq. inches to see if you can go that low with your reinforcing.

There is a difference.

## RE: Limits for Reinforcement of compression members

I've heard it called an "architectural column" when you do this.

This may be helpful in a situation where you have bumped up your column size to satisfy punching in the slab above...

## RE: Limits for Reinforcement of compression members

Excellent example. I have a question regarding that now. Now that you have showed that the 14.14 x 14.14 column works with some cover, c (which was the only way to get the reduced area of steel), do you have to detail the column such that the actual cover is 5.86-c (and you are essentially providing 1%Ag fo the "smaller" column), or can you detail identical to a typical column with cover c (and essentially use 0.5%Ag for the actual column)?

## RE: Limits for Reinforcement of compression members

## RE: Limits for Reinforcement of compression members

DaveAtkins

## RE: Limits for Reinforcement of compression members

## RE: Limits for Reinforcement of compression members

## RE: Limits for Reinforcement of compression members

## RE: Limits for Reinforcement of compression members

## RE: Limits for Reinforcement of compression members

I agree with jike - you design the column with the reduced section - get the steel - verify that it works (i.e. at 14" square) and then detail it as a normal 20" square column with normal cover.

## RE: Limits for Reinforcement of compression members

British code (BS8110) Asmin=0.004Ac

Euro code (EC2) Asmin=0.1*N/fy>0.002Ac ( N design axial force)

Australian code (AS3600) Asmin =0.01Ac reduced if As*fy>0.15 N

New Zealand code (NZS 3101) Asmin=0.008Ac

## RE: Limits for Reinforcement of compression members

As per Canadian Codes, you can still use 20"x20" column in your calculation for axial capacity with the ratio of steel as 0.5%(instead of 14"x14" column with 1% steel).

But the important thing is that you have to reduce the axial capacity by multiplying with 0.5[1+{actual steel % used)/0.01}]