Confused by AS3600-208 Wall Design Section

[MDILY]

In AS3600 - 2018 wall section, one condition we can avoid using confinement as columns (when design wall as column) is when vertical reo ratio is <= 0.01. But how can we achieve this when we design wall as column in the first place?

Also, what does "the vertical reo is not used as compressive reo" mean? Does that mean when we design the wall using P-M iteration we don't including the contribution of steel in compressive zone? Otherwise I dont get how we can avoid vertical reo in compression especially during an earthquake event when concrete cracks and the reo in compression zone will tend to buckle without the use of confinement?

 

[r13]

I think you should pay attention to the exception that follows the requirement of 0.01Ag for columns.

 

[rscassar]

My preference for wall design to AS3600:2009 & 2018 is to go straight to item A) N*<=0.5*phi*Nu.

It does look like the code committee are looking to amend the wording of this section for clarity

 

[Enhineyero]

The 1% vertical reo and restraint on the vertical reo are two different things.

The restraint on the column/wall vertical reinforcement is required when you have significant compressive stress. The restraint prevents the reo from buckling under high compression load.

The 1% reinforcement on columns is to allow for any 'accidental' eccentric loading to the column. The standard allows for a smaller min reinforcement for lightly loaded columns.

You can avoid the above if your wall is lightly loaded such that concrete alone or with very small amount of reinforcement is adequate to resist the design compression force. You will find that walls on most 'warehouse type' construction fits this condition.

 

[Complete_Columns]

Hi MDily,

Would be you able to provide an example of the design you are working with?

For the record I have seen this conflict arise before. I believe the wording does need revision. Read together, clause 11.7.4(b)(ii) and clause 10.7.1(a) imply the only compliant case would be a column-wall with exactly 0.01 reo ratio! I suspect this was not the intent of the standard authors.


Complete Columns

https://www.completecolumns.com/

 

[Retrograde]

I think the intention is that if you are designing a wall to Section 10, the requirements of 11.7.1 over-ride those of 10.7.1.

 

[r13]

I think for most of the walls with minimum eccentricity, if reinforced with 0.01Ag, the strength will be far exceed the actual required vertical reinforcing to resist the load. Thus, provide an Ase according to the calculated demand (< 0.01Ag) will satisfy the exception in 10.7.1, and also satisfy 11.7.4 (b)(ii), if horizontal reinforcement is provided accordingly.

 

[MDILY]

Thank you everyone for the replies.

Looks like the exception in 10.7.1 is the scenario for the 11.7.4 (b) (ii) then? I don't get how restraints has to do with vertical reinforcement ratio? What is the logic behind this?

And for 11.7.4 (b) (i), How do you understand 'vertical reo not used as compressive reo'? If it is in compression, then it will be compressive reo regardless of how we 'use' it. And if the reo is in compression and the restraint should be considered.

@ Complete_Columns
I dont have examples. It is just a general question.

 

[r13]

What is the provision 10.7.4 about? It is dangerous to interpret the code by looking selective parts only.

But, it seems to me that 11.7.4 is applicable for walls with small axial load that do not require compression reinforcement (concrete core alone is adequate), thus the reinforcement is provided for the sole purpose of resisting the moment, which can be seen as a "restrain" to the wall. In reality the reinforcement will feel compressive stress, but the stress level can be negligibly small, as compared to a wall that requires compression steel to resist the axial force. Make sense?