AS3600 - CL14.6.2

[Gishin1]

Hi there

Can anyone confirm that CL14.6.2 only applies to isolated shear walls with "discontinuous edges", and does not apply to walls within a closed core box?

I find that CL14.6.2.3 is quite onerous that where stress exceeds 0.15f'c, all verticals bars needing restraint. But then in a closed box, stress could be double that amount and not require restraint?

I guess it makes sense as an isolated wall will be more likely to fail in stability, so the compression rules only apply to them, but the tension reinforcement rules apply to both boxes and isolated walls to achieve ductility.

In this sense, for ductile core boxes, these walls are designed as columns, but don't necessarily need restraint if CL11.7.4 is satisfied. But then CL11.7.4 says that all walls must be restrained in accordance with CL14.6?

 

[mrlm]

Definitely applies to a closed core box too.

As 14.6.2.3 states "in any area of the wall".

 

[Retrograde]

I disagree with mrlm. In 14.6.2.1 it specifically states that boundary elements "shall be provided at discontinuous edges of structural walls and around openings through them". So I take 14.6.2.3 to mean that the boundary element extends from the discontinuous edge back to where the stress falls below 0.15f'c.

 

[blihpandgeorge]

i have understood to be a "discontinous" edge only, and thus not to boxes or inside angles of an L wall

 

[mrlm]

If only we had the code commentary we could put it to bed..... I jest.

Well, I'm happy to be wrong. I can see why using the wording in the code it could be read that way.

When the 2018 requirements first came out the company I was working for 'borrowed' another companies details to form the basis of theirs. The consensus in the office at the time was that any section in the wall where the compressive stress was greater than 0.15 f'c, the vertical bars require restraint (i.e. corners included).

I have since moved cities and companies and their details also show corners (or any wall section) where 0.15 f'c is exceeded requiring boundary elements.

So it is interesting that two (essentially three) separate consultancy companies have interpreted the clause in that way. It could be a case of not fully understanding the clause in the code and erring on the side of caution/conservatism.

I was positive it was an open and shut case but am now not sure. I would be very keen to see others opinions.

 

[rapt]

As long as the connection of the joining walls is detailed properly, the transverse wall would provide the "boundary element" for a closed core box.

But you would have to look at conditions at doors, lift openings etc where there is a discontinuous edge.

 

[rscassar]

I'm still on for designing mu=1.0

 

[Retrograde]

I'm still on for designing mu=1.0

That's our default starting point.

 

[Gishin1]

Thanks everyone for input.

Yes, my thoughts were when the code says "exceeds 0.15f'c anywhere in THE wall" it's still referring to the wall with discontinuous ends.

I'm still confused by CL11.7.4 (a): "for all walls in structures with a structural ductility Mu greater than 1.0, the vertical reinforcement shall be restrained in accordance with clause 14.6".
I'm assuming this doesn't override our conclusions, and this wouldn't apply to closed boxes. Therefore, for a core box, 11.7.4(a) wouldn't apply, but you still need to satisfy (b),(C), and/or (d) as appropriate.

My approach has also been to adopt Mu/Sp =1. This works well for say 30 stories+. But anything less than that, the Seismic loads are just too high and the ductile response is needed. Sometimes I wonder if the extra tension reinforcement at Mu=1 is better than all the detailing though..

 

[Retrograde]

Sometimes I wonder if the extra tension reinforcement at Mu=1 is better than all the detailing though.

I would often say yes, especially given the minimum reo requirements of 14.6.7.

 

[rapt]

I cannot see why 11.7.4 is confusing.

The relevant parts of 14.6 apply as they are defined in 14.6. So if it is a situation in 14.6 where boundary elements are required as discussed above, the the boundary element rules would apply. If not, then they do not apply.

It was deliberately worded like that so that we did not have to specifically direct designers to each particular instance in 14.6 for each particular case and having people tell us we missed a case, or it is too complicated or any of the other complaints that are continually made.

If I put a comment into the committee that people are having trouble understanding that clause, I would be laughed out of the room.

 

[Gishin1]

And yet there are numerous posts trying to clarify the new code requirements. I've had discussions with others from multiple design firms about similar issues. If only there was a way for practicing engineers to get in contact with the committee directly about these issues, but of course, the committee would no doubt be inundated with questions, which is why the committee is near impossible to reach, and we are left to forums like this.

And that's exactly how the committee likes it, obviously.

The code is written with all sorts of vague wording on purpose to give the code authors a way out if anything ever goes wrong. And then they just say "it's not a cook book, you have to exercise judgement". But when engineers raise questions, they just "laugh you out of the room".

The codes being confusing is a problem because engineers use that as a way to find loopholes around the new requirements, which they are doing.

 

[rowingengineer]

Strangely I find most committee members helpful and open to assist in most matters.

 

[Agent666]

If I put a comment into the committee that people are having trouble understanding that clause, I would be laughed out of the room.

Thats not necessarily your problem if there's some fact to it, seems to be there are a lot of questions here in this forum asking for clarification all over the AS3600 code, and going round in circles related to the intent of some clauses. Sometimes when it's explained it dawns on them what was trying to be said, other times they still don't believe because it goes against the way they have been doing things for years and suddenly designing something correctly is a problem!

I guess if the peoples on codes are not prepared to listen and make things clearer or provide formal clarifications for the target audience which is as far as I can tell people with very limited seismic experience then you're fairly stuffed and people will be interpreting things 101 different ways which don't necessarily align with the writer's intent. Sure there will always be rule twisters/breakers, but I think most people genuinely want to be doing it right. But what is right when there is ambiguity in those code words.

Really if potentially confusing clauses are being included (many of the questions here elude to this), then these areas should be backed up by industry advice that clearly explains these nuances and how to apply them correctly in line with the writer's intent.

Maybe that elusive commentary would help?!

With seismic experience it's relatively clear what AS3600 is trying to generally say to me, although not always worded in the clearest way.
Without this experience it seems to me it's left to Aussies with minimal seismic experience and/or no formal education in seismic design to try fill in the gaps and fudge their way through it. If people on code committees cannot see the potential for confusion in clauses given that target audience then that seems like a recipe for disaster.

https://engineervsheep.com

 

[rowingengineer]

What is the intended target audience for a code that is fully sed? Maybe we need a red book for Aust

 

[Agent666]

Well engineers obviously, but if the general audience lacks the knowledge of seismic side of things to effectively use or interpret it, that's a bit of a failure of the entire industry. I assume in universities they are now teaching this stuff, but I'm guessing it's probably taught by academics who may have zero seismic experience.

Yeah something like the "Red book" here in New Zealand but for Australia would aim to answer all these interpretation issues. There was some Australian document by one of your industry bodies that aimed to do something similar, the exact document/authors eludes me at the moment. Maybe by some reinforcement or concrete industry body from memory, I thought it explained some of the concepts quite well to be honest, the sort of things like why does the code do it this way, we'll its because of this... .

https://engineervsheep.com

 

[Retrograde]

I know it is not necessarily the committee's fault, but I find it ludicrous that 4 years after the new code was released we still do not have a Commentary.

 

[IDS]

I received an e-mail from SRIA a couple of weeks ago about the publication Agent666 is probably referring to:

"I have been reading all of the recent communications and just a reminder that you can still download the SRIA’s free pdf Guide to Seismic design and detailing of Reinforced Concrete Buildings in Australia It is available from the link at the bottom of our sria.com.au home page. It was published in 2016 and was a precursor to many of the more recent seismic upgrades in AS 3600:2018."

The link to the free download is:

https://sria.com.au/seismic-registration

Also the Australian Earthquake Engineering Society produces a commentary to AS 1170.4 which was recently updated and is available as a free pdf download:

"For those of you who did not attend the conference or see this announcement elsewhere, AEES has published an update to the AS1170.4-2007 Commentary - 2nd Edition (2021) which is available as a free download at:"

https://aees.org.au/product/as-1170-4-commentary-2021/

Note that if you go to the AEES site and go to their download link from there, it still links to the previous version, and makes no mention of the latest update.

Doug Jenkins
Interactive Design Services

http://newtonexcelbach.wordpress.com/

 

[rapt]

The committee has no say in access. The rules are set by Australian Standards.

Where things needed rewording we have tried to help in the amendments.

Against Standards rules I have answered questions on this site where I think something is open to interpretation as well as passing it on for committee consideration.

We have actually made the wording overly precise in some cases to try to cover cases people may be unsure of, against the wishes of some on the committee.

In this case, I give up! There is nothing vague about the wording of this clause.

 

[Settingsun]

I assume in universities they are now teaching this stuff

Not according to the young people I work with.