Slab to jumpform wall connection

[BentEng]

If you have a continuously poured, jumpformed concrete wall, what are the best ways to then connect a slab into the wall? Specifically looking for options where the slab is on both sides of the wall.
The wall is 250thk and the slabs are 200thk. Typically our firm specifies Ancon keybox, or alternatively cast-in ferrules.

What are everyone's thoughts on cast in conduit and feed through lap bars, top and bottom, and still rebate? Obviously trying to avoid any gap between the void and the bar, but also not sure if its a good idea have the conduit left in the wall. This avoids having a keybox on both sides of the wall, and provides better continuity of reinforcement between both slabs.

 

[rscassar]

my preference is the rebox. Easy to install, good anchorage with the u-bars. This is for lightly loaded connections with a couple of metres trib width to support. When the loads are getting bigger I go the ancon or peikko inserts. Have done localized blockouts when the loads are large and the bearing connection is the way to go. Never tried sliding the rebar thru a conduit.

I saw a similar detail in the UK a bit, where metal deck would span onto the bottom flange of an unequal flanged I-beam, and holes would be drilled thru the web and H20 or H25's would be slotted thru

 

[Trenno]

I assume one of the slabs is inside the corebox (eg stair landing, lobby slab etc), therefore the slabs either side of the wall will be poured at vastly different times.

 

[BentEng]

rscassar - Yes I prefer rebox/pull out bars, but we are getting push back more and more these days on specifying them.

Trenno - the stair and landing will be pour later, but with this arrangement, the lobby slab will be poured with the main slab, so sleeved bars would be anchored on both sides for this area.

I found the sleeved conduit detail on some legacy project drawings but have no information on the performance, or how installation went. So long as the sleeved bar is snug, there shouldn't be any issue?

 

[SRL V1.0]

Do you need the continuity by design?
Personally I wouldn't entertain continuity through a core wall unless it was a cantilever beyond the core wall.
Keyboxes are the way to go for the majority of situations. For transfer beams you can use couplers (ancon produce 'coupler boxes' for ease of install). Also make sure that your details call up the rebate as "full-slab/beam depth", subbies like to avoid it in beams where they have keyboxes top and bottom and no rebate between.
Be careful with ferrules. They have much less(!) anchorage and therefore capacity. Go through the specific ferrule design guide with your spacing and edge distance parameters.

 

[Just Some Nerd]

First choice for me is definitely rebox/keyboxes/pullout boxes (whatever they're called) but installing it on both sides of the wall can definitely be an issue depending on wall thickness and bar size, thinking mainly about horizontal bars that anchor the boxes. Often made worse by the slight difference in levels when stepping into a stairwell too.

If dealing only with shear loads and no pullout/tensile loads, ferrules might be pretty good in terms of capacity, but they're not necessarily any easier to install in a jump-form scenario than post-installing rebar by drilling & epoxying a decent sized bar.

I'm a bit wary of coupler boxes/keyboxes for any transfers as the potential loads are very high if in a situation where jump form is economical (generally a taller tower). Much prefer to block out a pocket in the concrete and let the beam get poured sitting fully on the wall.

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

 

[SRL V1.0]

With the blockout detail - What do you do when there's a lift shaft on the other side?
In Melbourne and in my experience Concrete Structure Sub-Contractor's would not be able to / be willing to build this.

 

[Just Some Nerd]

With the blockout detail - What do you do when there's a lift shaft on the other side?
In Melbourne and in my experience Concrete Structure Sub-Contractor's would not be able to / be willing to build this.

Haven't actually run into the issue yet of anyone pushing back on leaving pockets in the wall though I'm Sydney based and it's been very few in number so far. The size of the transfer beams made the necessity pretty evident I think. I'm not sure how the lift shaft affects the scenario compared to the stairwell as there's no lift going to be installed for a very long time, unless it's an issue with having a work platform to form up the inside face? So far I've seen builders use foam blocks (lol) to prevent concrete filling a portion with continuous wall reinforcement....it's not an elegant solution by any means.

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

 

[SRL V1.0]

It's about 'how the Builder would form up the inside face'? If the transfer beam is a few floors up does the Builder need to erect a scaffold inside the shaft to be able to access the edge formwork. That would be a lot more work compared to providing couplers etc. given the connection is able to work..

 

[Just Some Nerd]

If the transfer beam is a few floors up does the Builder need to erect a scaffold inside the shaft to be able to access the edge formwork

I think this is what has been happening. It's doable, even on jobs without jump form I've seen builders erect scaffolding inside of lift shafts where they need it to form up the separating way between the lifts if present, and that continued the full height of the building (not too high, maybe 8 floors total). I imagine it's far more problematic when the transfers are not close to the base.


Edit: as an addendum, yes it's much easier to use couplers provided the shear transfer works and the builder is happy to install them. One potential problem I see is if using beams, the couplers might not align well with the corners/eyes of stirrups/ties when installing them later
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Why yes, I do in fact have no idea what I'm talking about