Definition of a concrete columns vs. a wall

[WillisV]

Could someone provide me with a code reference that indicates when a certain member is defined as a column vs a wall (aspect ratios etc?). Looking more as it pretains to min. reinforcing provisions and fire rating applications as opposed to strength design.

 

[kslee1000]

I doubt there exists such reference. The following is merely my 2 cents.
For reinforcing purpose, I define a column as a long compression member with both axes having similar structural characteristics/responses when subjected to same type of loadings. Otherwise, it is a wall. (For example, shear deformation is more dominate along the axis of wall, but not the case in the other direction. Others may have better examples, please address)
For fire rating, I think you have to judge it base on how important it is to the safety/structural integrity of the entire structure and the failure mode. To me, it is a column if substantial collapse would be triggered by fail of such compression element.

 

[slickdeals]

I remember seeing something that classified walls and columns based on b/d ratio in the Florida Building Code. I will look for it. I think i remember b/d ratio > 4.

 

[youngstructural]

I have often wondered about this same question, and have never received a satisfactory answer...

My personal belief is fairly simple, and similar to kslee1000's approach; It has to do with behaviour. If the element will behave primarily as a compression member under vertical loading, it is a column. Buckling checks, stirrups to stabilise the compression steel, stirrups to permit safe formation of plastic hinges, etc, etc, column detailing approaches are required. If the element acts primarily as a flexural member, or the compressive load can be seen to dialate out accross a length of the element from point of loading, that is a wall.

I don't buy the argument of "either way is fine" which I have seen before, but have only my guy feel to back me up. I don't think you can expect a section to behave as a wall or a column just because you say it will... Nature will do whatever comes easiest.

I have heard ratios battered about previously as well, everything from h/d > 6 to h/d > 3. I will be very interested to see if anyone can post a code reference!

Cheers,

YS

B.Eng (Carleton)
Working in New Zealand, thinking of my snow covered home...

 

[concretedoc]

The same question was asked and answered in the October 2003 issue of Concrete International magazine. If you're an ACI member you can access it at

http://www.concrete.org.

Click on "Bookstore and Publications," then on "Concrete International." On the CI site click on "Archives," then on "Back Issues" then find October 2003 and click on that. I'm not sure it will help with your concern about fire resistance because that's not mentioned in the answer.

 

[msquared48]

To me, specifically for concrete, if there are ties required to constrain verttical reinforcing, I would consider it a column element. Without the ties, then a wall element.

Mike McCann
MMC Engineering

 

[WillisV]

@concretedoc - yes I am familiar with the document you mention, unfortunately that answer is not really satisfactory in this context. I will try to ask ICC for a code clarification in the context of fire rating provisions.

As an FYI ACI 530 defines a column for masonry as b/d ratio <3.

 

[UcfSE]

See ACI 318-05 page 29 under the definition of a column. Is that what you were looking for?

 

[WillisV]

Nope! Thanks though. What I'm really looking for is a clarification based on IBC fire ratings. There are different minimum thickness requirements for walls and columns. So is a 8"x72" member a wall or a column for fire resistance? Where is the transition made? Its not defined as far as I can tell...

 

[kslee1000]

As suggested before, for fire rating, you have to judge from the function of the element you are evaluating. A column is a single element for which failure can trigger a series of adjacent elements to follow suite, and likely resulting in structural collapse over a significant areas, if not the complete building/structure, and render the building/structure un-inhabitable. On the other hand, the failure of a wall could cause severe "localized" damages to an extent but collapse is highly unlikable.

Assign rigid aspect ration can fool you into making trigical mistakes without thinking the consequence. For example, due to aesthetic reasons, a short wall (pier) with relative large aspect ratio can serve as main column in many modern buildings. Structurally it can be designed as a wall, but functionally speaking it is a column. I hope there is someone agree with me on this, and can provide better explanations and examples.

 

[concretedoc2]

ACI 318 in the "Definitions" section defines columns as "member with a ratio of height-to-least lateral dimemsion exceeding 3 used primarily to support axial compression load."

 

[kslee1000]

The inclusion of the word "least" confuses me, by that, most of the walls should be considered as column as long as Height/Thickness > 3, no matter how long the walls are. Do I mis-understand something?

 

[WillisV]

The definition in ACI318 is not meant for this situation - it is intended to define the difference betwen a "column" and a "pedestal" not between a column and a wall.

 

[engn555]

The Canadian conc code A23.3 cl.2.2 says a wall is "a vertical slab element, ..., in which the horizontal length is at least 6*thickness or 1/3*height".
Otherwise it would be a column.

 

[kslee1000]

engn555:

Does Can. code explains the logic behind the suggest ratio?
Very curious to know. Thanks ahead.

 

[engn555]

Sorry, I cant find an explantion other than the definition given above.

 

[DonPhillips]

I cannot find a specific definiation in the IBC to distinguish a wall from a column, except

2102.1 General. The following words and terms shall, for the purposes of this chapter and as used elsewhere in this code, have the meanings shown herein.

WALL. A vertical element with a horizontal length-to-thickness ratio greater than three, used to enclose space.



Don Phillips

http://worthingtonengineering.com

 

[WillisV]

Thanks for checking Don - As that is in the masonry chapter I have to believe it only applies to masonry and is just copying ACI 530 as mentioned in my 2nd post.

 

[youngstructural]

I think the resistance in creating a more explicit code clause relates to the fear that engineers might view it as a hard and fast rule, rather than the more rational behaviour approach.

Cheers,

YS

B.Eng (Carleton)
Working in New Zealand, thinking of my snow covered home...

 

[kslee1000]

Youngstructural:

Quite correct. Especially the exact/explicit codification has legal consequences/implications.