AS3600-2018 - Detailing for grouted ducts in precast walls 1

[li0ngalahad]

Hi
I am a bit puzzled about clause 17.7.5 on the AS3600-2019 code and I was wondering if anyone can shedsome light on it.

17.7.5 Grouted ducts to joints
Grouted ducts used to join prefabricated elements shall be fully confined using Ductility
Class N reinforcement anchored perpendicular to the duct in accordance with Section 11.

As usual, AS3600 is vaugue and unclear, and prone to be misinterpreted, especially without a commentary. It's quite ridiculous really, especially when you compare it to ACI or EC2. I was disappointed to see that the Amendment 2 Draft shows nothing about this clause.

Anyway, my questions are :
1) How do I design this "full confinement in accordance with Seciton 11"? Section 11 does not talk about full confinement as far as I know??
2) What does "perpendicular" to the duct mean? In a precast wall, horizontal reinforcement is anchored perpendicular to the duct, however I don't see that doing much in terms of confinement.
3) Do we really need to detail this even if my structure is designed with ductility 1? And if so what is the reasoning behind this? As long as my lap is in accrodance with AS3600, and I assume ductility 1, I would think such painful detail can be waived??

I have found a document from the NZ commission on the 2011 Canterbury earthquakes that talks about this, with a lo more info in terms of detailing and calculations. I wonder if anyone here is using the same formula and detail?

 

[Agent666]

I'd never use them personally, never seen them used in NZ either.

But that paper I linked to above in 26 Oct 20 02:54 post seemed to suggest they worked ok, but not as good as metal ducts basically.

 

[QSIIN]

I don't like the idea of grout plastic grout tubes.
I find it interesting that there's so much discussion and focus in the industry about development length, lap length, anchorage, etc, but grout tubes are just thrown around out there without much thought.

I suppose for compression only elements I'd be less concerned, but I don't really understand how tension splicing works through grouttubes in all the precast cores and shear walls that are popping up all over the place..

I've seen details where the lap in the grout tube is less than the lap of the bar itself...with the justification that the development length is enough, without any theory behind the anchorage of the grouttube..