Tilt-up External Free-standing Firewall Connection 3

[apsix]

I'm looking at using precast concrete panels, approx 8m high x 3 m wide, cantilevered from the base.

Are there any recommended clever methods of achieving a fixed base? At this stage I would consider both; footings cast before and cast after the erection of the panels.

Thanks.

 

[hokie66]

Cast the footing with a big slot to receive the panels, set the panels, then grout around the panels.

You can also set the panels on a regular footing and tie the panels to floor slabs. Need to make a positive attachment to the floor slab. This method restrains the slab, meaning more likelihood of undesirable shrinkage cracking.

Having said this, if these are external bearing walls, cantilevered walls should not be used. Walls should be designed to fall inwards when the steel collapses. A wall which is cantilevered will curl in an intense fire, making it lean out. The steel will be tensioned, and the connections can fail instantaneously, causing the wall to fail and fall out.

 

[apsix]

Thanks hokie

They are freestanding firewalls between transformers in a sub-station, so no issues re connection to steel framing.

 

[rowingengineer]

Hokies method with the cast-in slot is my preferred method, I always ensure this is a tappered slot, makes construction a bit easier.

When in doubt, just take the next small step.

 

[csd72]

In the past I have used ferrules in the slab on either side and the footing at the base to take the push/pull from the overturning. This has worked well and is cheaper than casting a slot in the footing.

 

[asixth]

hokie,

what do you mean when you say a positive attachment?

 

[spats]

I lock the tilt-up into a secondary pour, as shown in the attached detail.

 

[hokie66]

apsix,

I mean providing a tie between the wall and the slab. Something like spats showed, but it can be done with ferrules and screwed in bars or in other ways. Don't just depend on the slab each side to restrain the wall, as the slab will shrink away from the wall.

 

[csd72]

spats, if its connected to the slab at the top, why do you need to embed it into the footing?

Those number4 dowels would be a pain, better to have a cast in threaded insert (ferrule) that wont get in the way during lifting.

I do love the footing detail though (when its necessary) I have used similar myself.

 

[spats]

The detail I sent was specifically for a outdoor smoker's lounge, where there happened to also be a slab. It's a small area, approximately 20' x 25'.

I would never consider using the slab for the stability of the wall anyways. What about when it's under construction? You can't remove the braces until the slab is in. What if they decide to cut out the slab in the future, not knowing it's integral to the stability of the wall? Besides, you would have to bury the footing deeper to get a decent moment arm between the slab and the footing. All-in-all, not a good idea, in my opinion.

cds72 - I assume your talking about the slab dowels. Not a problem at all. I've been using them for 20 years and haven't gotten any complaints. They're easily tied to the reinforcing mat, and are not in the way at all during lifting.

 

[hokie66]

They would certainly be in the way if you are stack casting.

 

[csd72]

spats,

I agree with the issue regarding the cutting of the slab - it does happen. But if there is a roof at the top restraining it then it will be stable under normal conditions.

 

[spats]

In my experience, stack casting is not used all that much. However, my drawings always contain an "alternate stack casting detail", which uses a deformed bar field welded to an embed plate. I know some kind of ferrule insert is preferred by some engineers, but they're not cheap, nor is having to thread the slab dowels.

cds72: since we were talking about cantilevered walls, there is no roof to brace at the top.

 

[hokie66]

Interesting. In Australia, most of the tilt up jobs use stack casting and ferrules. And I'm sure they don't do anything they think is expensive.