Wood railing post on concrete slab edge

[Buleeek]

Hello everyone,

I'm designing a repair for a pool deck. A 4x4 wood posts is embedded in a 5.5" concrete slab, approximately 4" away from the edge. Needless to say, the slab cracks at 45deg from the corners of the post towards the slab edge.
The owners would like to keep the wood posts instead of switching to aluminum. Is there a way to install the wood post on top of the concrete slab and the post will carry the moment at the bottom (200# * post height)? Or maybe there is a way to embed the wood post in 5.5" concrete slab so it won't crack?

See attached drawing.

 

[jayrod12]

There aren't really great details for that. Simpson Strong-tie has a moment resisting post base, however that would require casting it into the concrete.

Any sort of enlarged baseplate would push the anchors extremely close to the edge of the concrete as well, meaning next to no capacity.

All in all, that's a bad detail. Unfortunate for the owner, but not recommended nonetheless.

It sounds as if there's no reinforcing, or minimal reinforcing between the wood post and the edge of concrete. Is that correct?

 

[phamENG]

If the insist on that look, the best thing to do is probably to cut out s section of slab and wall and pour a larger block of concrete in there. Then use a Simpson Moment Post Base at whatever spacing you need to make it work. Then they can put trim on the base to cover the steel.

Still not great, but should 'work' if you can reconnect to the existing slab in a reasonably meaningful way...

 

[Buleeek]

There might be a slab reinforcement, but nothing special for the wood post. Thanks for your help.

 

[jayrod12]

Yeah without notable reinforcing to prevent that outward breakout failure, there's not much you can do. Even an aluminum railing mounted that close to the edge, with minimal reinforcing, you may still have the same breakout failure. The concrete really doesn't know or care what material the load is coming from.

 

[Harbringer]

Move the posts outside the slab so that face of post = face of CMU. Anchor through post into slab at top and into CMU some distance down at bottom.

Sounds like the owner will have to do this to multiple posts but will get to keep the wood look.

 

[Harbringer]