What fence post base attachment to existing concrete?

[derekthemurray]

I'm replacing my front fence with a timber picket fence, 1.2m high.  I have an existing concrete base, about 150mm wide.  My initial thought was that I would have to chop out the concrete to sink the timber fence posts into the ground so I could concrete them in.  However I'm hoping I can use a metal post brace instead to anchor the post to the top of the concrete.  Could I use these?

https://www.bunnings.com.au/pryda-90mm-m10-heavy-duty-bolt-down-post-anchor_p0503052

Will they have enough lateral strength to hold up a low fence?

[JacobZ]

Hi @derekthemurray,

Thank you for your question.

A couple of questions in return.

Would you be using them for every post, or would this only be for 1 post?

Do you know how deep the concrete is?

If it was a full height fence, I would absolutely not recommend it. Fences are subject to a wind loads which exert a surprising amount of lateral force over the extent of a full-length fence. 

If it was one or two posts, you could probably get away with it because the concreted in posts would help to brace them, but if it was every post along the fence, I wouldn't be confident.

For peace of mind and the long-term strength of the fence, it would be better to remove the concrete so you can concrete in the new posts.

You might get away with it, but I couldn't say with any confidence it would last.

Allow me to tag @Dave-1, @Nailbag and @AlanM52 for their thoughts.

Jacob

[AlanM52]

Hi @derekthemurray,

Please post some photos.

Cheers

[Nailbag]

Hi @derekthemurray 

If this rebuild was part of a property prep for sale, then maybe there are a few shortcuts. But if this is your long term home then if it was me, I would be starting fresh as being the best long term solution. It will also be a lot easier than attempting to fix any form of post mount to an undetermined underground concrete base. It will also have a non-level top surface which will be very problematic in trying to make the fixing posts perfectly plumb (vertically level). and then you also have no idea how strong it will all be,

Nailbag

[Dave-1]

Good Evening @derekthemurray 

Without seeing any pics my thoughts tend to go along the same lines as @Nailbag's. You could get away with using spacers to level the stirrup, if its multiple posts then it comes down to how thick the concrete footing is, if its like a thin concrete edge to a garden or path (50mm thick) then its a nope, if its 100mm with reo, Im still hesitant as if the wind blows thats a huge sail on top of the concrete instead of down into a proper concrete footing. (think pivot weighting)

Dave