When to consider designing a concrete shear wall instead of a column? 1

[ErZaZee]

In some regions that I've visited they used to design columns wherein the small to long dimension ratio of a concrete column cross section is less than 25%.

When is the right time to consider designing a shear wall instead of a column?

Can you please guide me on some code provisions regarding this matter.

 

[ishvaaag]

What you name is the usual consideration in Spain. I don't think (that I remember) is based in any code. In my view, it is the code which has to introduce the particular specifications to which the design of particular structural parts or systems need be subject to.

So, in absence of code clarification, you need to pursue the matter according to your structural understanding. Overall, with the same geometry, the behaviour will be the same (that simplification is subsumed in our elastic analyses) ... yet it will be influenced by the reinforcement we include; more or less following the idea that our structures can't resist but in the ways we endow them to be able to.

 

[DST148]

I think you meant the ratio greater than 25%.
ACI 318-05, Chapter 2, Commentary - The term compression member is used in the code to define any member in which the primary stress is longitudinal compression. The differentiation between columns and walls in the code is based on the principal use rather than an arbitrary relationships of height and cross-sectional dimensions.
UL Directory of Fire Resistance defines walls as members with a ratio of length of wall to width of wall greater than 4.In that case the minimum thickness of the member, cover etc. are much less than for a column because a wall may be exposed to fire from one or two sides but a column could be exposed from four sides.
We typically design members forming part of an enclosure or separation as walls / shear walls and isolated members as columns.

 

[ErZaZee]

Small to long dimension less than 25% meaning the small dimension of the column cross section is 25% of the long dimension.

Or the long dimention is more than 4 times of the small dimension.

If there is no definition to differentiate the two in terms of cross sectional dimensions, is there any provision in ACI or other structural codes regarding the minimum thickness of structural walls and minimum cross sectional dimension of a structural column?

So what do you prefer, design a column with a cross section of 0.9 x 0.2m or a structural wall of the same dimension? Both will be subject to gravity and lateral loads.

 

[DST148]

I am referring to ACI 318 - 05.
In my last post I have spelt out how ACI differentiates between walls and columns based on the use.
Columns are designed by the provisions of Chapter 10. With the ACI 1971 code, minimum sizes for columns were eliminated to allow wider utilization of reinforced concrete compression members in smaller size and lightly loaded structures.
Chapter 14 is devoted to walls using empirical method. ACI code permits walls to be designed using the principles stated for column design as well as by the empirical method of Chapter 14. The minimum thickness of bearing walls designed using provisions of Chapter 14 shall not be less than 1/25 the supported height or length, whichever is shorter.
The requirements for the vertical, horizontal, spacing of steel, design for shear, clear cover, fire rating criterion are very much different for walls and columns.
Since you have all the info about the location of this member in the over all scheme of things and the forces on the member, you are better positioned to make a design decision.
One thing is certain - you can not just go by the ratio of the cross-sectional dimensions.

 

[DST148]

Further to my response dated October 31, 2011----
Although concrete code has done away differentiating between a column and a wall based on cross-sectional dimensions, the masonry code has stuck with that criterion.
As per ACI 530-02 - Building Code Requirements for Masonry Structures:
Column is defined as an isolated vertical member with a horizontal length to thickness ratio less than 3 and whose height is greater than 4 times its thickness.
A wall is defined as a vertical element with a horizontal length to thickness ratio greater than 3, used to enclose space.

 

[ErZaZee]

Thanks for your answers DST148.

I'm pretty well aware that you can not just go by the cross-sectional dimensions when designing but once and a while I encounter structures where both options are possible, as far as I know, and as you mentioned, ACI 530-02 is stuck with this criterion meaning, there must be some sense to this criterion.

"A wall is defined as a vertical element with a horizontal length to thickness ratio greater than 3, used to enclose space."

Used to enclose space??? What if it does not envelop a space? You can't consider this as a wall? A long straight wall is not a wall but a column? Is that it?

It should have been clear if they did not include that clause hehehe...