Post Tensioned Concrete - Requirements for PT running through core

[efFeb]

Good morning,
I am working on a post tensioned concrete slab, and have an opening cutting off my core wall from the slab.
Usually I would run tendons through the core wall, ensuring that they can exit the other side. From my understanding, this is to meet integrity reinforcing requirements.
If I can provide enough integrity reinforcement in the opposite direction, is there a concern with dead-ending tendons at the face of the opening?

 

[rapt]

Is the tendon required in the slab to the right of the penetration? If yes, it is better to move it down outside the wall and have it continuous. If not, it does not matter.

The connection to the core wall should have a lot of un-tensioned reinforcement into the wall anyway.

Or tell the Mechanical engineer to move his void by the width of the wall. It may have a non-loadbearing wall which lines up with the structural wall around it anyway!

 

[1.392DL]

I don't believe traditional integrity reinforcement applies to walls. Maybe if you're using an R=6 and providing special columns each side, but even then the failure of core walls should be in bending but not lead to collapse. Integrity reinforcement is to protect against progressive collapse where either the column fails or deck punching fails. We typically don't run PT thru the cores at all. I'm curious what others experiences are though.

 

[KootK]

1) Once upon a time, I really thought that I understood Canada's integrity steel requirements. That perception has waxed and waned over the years I'm afraid.

2) A while back, steveh49 turned me on to the article below which, I believe, forms the basis for integrity steel, at least in the Canadian context.

3) As I understand it, and per the sketch below, two things are required in order to have satisfied integrity steel requirements in Canada:

a) The reinforcing provides a backup mechanism of punching shear resistance at the columns to kick in once a traditional punching shear failure has developed.

b) The reinforcing provides a "hanging net" system to support the slab once traditional slab flexural resistance is no longer viable (because of the punching shear failure).

 

[KootK]

b) The reinforcing provides a "hanging net" system to support the slab once traditional slab flexural resistance is no longer viable (because of the punching shear failure).

To satisfy this requirement, the integrity reinforcement needs to be well developed into panels adjacent to the panel being "hung". As such, I believe that you require integrity reinforcement at each corner of your shaft wall core, in each direction. Which set of bars you'll be utilizing for any given punching shear event will depend on which adjacent slab panel will need to be supported by the hanging net thingy.

Similar to rapt's comments, I would normally:

a) Run your PT out side of the walls and past any openings and;

b) Satisfy your integrity reinforcing requirements with rebar set out as shown below.

I'd be pushing pretty hard to have your mech opening shifted slightly to facilitate this.

 

[Just Some Nerd]

We typically don't run PT thru the cores at all. I'm curious what others experiences are though.

I've not seen integrity reo provided for core walls, nor have I seen in practice a PT duct through a wall like that. I'm not sure anyone really wants PT to satisfy integrity requirements, since you'd typically place the tendons higher over supports but would need to be lowered to perform as integrity reinforcement, or at least that's my understanding of it. There's also the issue (question?) of what happens to a prestressed tendon when the slab fails in the manner you'd want integrity reo for

 

[KootK]

I'm not sure anyone really wants PT to satisfy integrity requirements, since you'd typically place the tendons higher over supports but would need to be lowered to perform as integrity reinforcement, or at least that's my understanding of it. There's also the issue (question?) of what happens to a prestressed tendon when the slab fails in the manner you'd want integrity reo for

My understanding of that is:

1) Folks do not drop the PT strands used for integrity reinforcing.

2) It is anticipated that the strands rip out of the top of the concrete until their elevation within the slab drops low enough to arrest that.

I know, it's a bit unsettling really.

 

[Ingenuity]