AS3600-2018 Walls vs Columns (Again..)

[Gishin1]

Hi All,

I know this topic has been beaten to death on here, and no conclusion has really been made to clearly define the difference between a 'wall' and a 'column'.

The most current AS3600-18 Amdt 2 has definitely made steps in the right direction, but ultimately, engineers can, and are, still designing <=50MPa 'columns' to section 11 capacities, forgoing any out-of-plane slenderness checks to Section 10, moment magnifier method or other.

I've recently come across this disturbing paper, endorsed by Engineers Australia & the Australian Earthquake Engineering Society (AEES) (well, the logos are on the paper).
This paper is essentially encouraging engineers to adopt 200x1000 blade columns, and use Section 11 to design them, as you can get better capacities with less reinforcement.
The conclusion notes that a 200x400 sized element would work just as well!

Given this paper was presented at an AEES conference, I'm surprised to find that the paper instructs the user to simply adopt non-ductile design for these blades, without any consideration of with local/global ductility demand.

I have peer reviewed numerous other projects where 'columns' such as these are being built with 50MPa and mesh reinforcement in high-rise structures, because the Section 11 capacities are so much better than Section 10. Papers like this completely undermine the peer review process/sound structural engineering/all the effort gone into the new code and commentaries, and provides 'evidence' that this approach is acceptable.

Does anyone else think this is an issue? I understand that the moment magnifier method can be overly conservative in some situations. Am I too conservative in my approach of using Section 10 Column Design to design columns. Are 200x1000 and 200x400 50MPa 'walls' acceptable?

 

[Retrograde]

I think you have misrepresented the content of the paper you linked to. They have presented a factual study of some idiosyncrasies in the way walls and columns are designed in AS3600 and recommended that the Standard be more clear on the definition of a wall v. a column. Note that a 1000x200 element can be considered a wall in ACI and Eurocode also.

 

[Just Some Nerd]

Definitely on team column over here....simplified wall design does not instill me with confidence when it comes to any structure larger than say a 3 story luxury home. One of the major incentives to design as a wall instead of column is to allow them to use something like AFS/Dincel forms on site since you don't need to install inner ties...I'm not personally a fan of those systems in general and how unreliable it is to get a column/wall without voids inside it.

I do kind of wonder about one thing though, something I've seen done often is designing as a column for loads but when it comes to FRL requirements checking as a wall? Not sure if that's a problem to be honest.

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Why yes, I do in fact have no idea what I'm talking about

 

[rscassar]

I think simplified wall method should go. I stopped using that around 2016. I think every vertical element should be designed using and interaction diagram and the slenderness rules of Section 10. My definition of a column is that any one of the following 4 is satisfied than must be designed as a column:

- Aspect ratio less than 5:1
- Story height / largest cross section dimension less than 3
- The vertical element will want to exhibit reverse curvature or the expected frame action bending in the strong axis under gravity loading
- The vertical element attains the tributary floor load in the immediate vicinity of the element with no opportunity of re-distribution in the event of a localized failure

 

[rapt]

Racassar,

Couldn't agree more.

It was introduced at a time before computers to try to provide a simple conservative design solution, when concrete strengths were low and really for lightly loaded walls.

But as usual it has become the real way it works.

Bit like rectangular stress block. I have even had academics tell me it is the more correct solution!

And in this case, there are still influential academics who want to keep it because people like using it.

For any "real" wall, design it as a column.