# Forum Home Renovation Brickwork  Attaching timber posts to top of concrete block wall

## jmn

Just want to know the best way to attach a timber post on top of a concrete core filled block wall.  
Would you 
1. Either use a bolt down post support or a high wind support bracket which would be concreted into the wall.  
Or  
2. Place the post inside the hollow bit of the block and then concrete into place.  
The highest part of the wall is about 800mm from street level.  
The fence posts probably 90x90mm and 1300mm tall.   
Sent from my iPhone using Tapatalk

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## DuckCommander

Cast in fin plate into blocks with min 2 bolt to timber post connection with large ie 200mm spacing between bolts. Long axis of fin plate perpendicular to fence direction. Both you're proposed options I would not consider adequate as a high wind brackets are not designed for bending loads (wind on fence) just uplift. Timber cast in concrete is not a durable connection.

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## ringtail

High winds will be fine. It's a bloody fence FFS.

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## DuckCommander

Wow once again others opinions dont matter unless you're one of the few renovateforum.com posting elite.

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## OBBob

I'm sitting on the fence for this one.  :happy:

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## intertd6

It just goes to show the shallow depth of knowledge or experience level in regards to safety & design, there was a accident in Melbourne where a fence blew over in high winds & caused the death of 3 people or in Sydney where a temporary fence blew over & killed a child, rough enough, isn't good enough.
inter

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## r3nov8or

At only 800mm max high I would run the posts to the ground, either 'inside' or 'outside' the wall. Rather than rely on just the top course (or 2) of brick. The type of fence would also matter

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## ringtail

> Wow once again others opinions dont matter unless you're one of the few renovateforum.com posting elite.

  
Bwahahaha. Not at all. Cast 600 mm high winds in line with the blocks and bolt a hardwood post with 2 xM12's and there is no way that wind load will move it. Absolutely no way. It might wobble a bit if the posts were 2 mt high with zero gaps in the pickets bit I believe it's not a big fence and it will be pickets. I would be more concerned with the integrity of the block wall than the fence sitting on top of it.

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## ringtail

> It just goes to show the shallow depth of knowledge or experience level in regards to safety & design, there was a accident in Melbourne where a fence blew over in high winds & caused the death of 3 people or in Sydney where a temporary fence blew over & killed a child, rough enough, isn't good enough.
> inter

  
What sort of fence was the Melbourne one ? Temp fences don't count. They get blown over every day. There is a big development happening at the Brisbane tennis centre and to advertise it theses clowns got a full on steel structure about 4 mt x 4 mt and about 4 mt in the air ( on posts). The post holes looked to be about 600x350 based on the concrete attached to the posts as the complete structure lay smashed on the ground 2 days after installation.

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## pharmaboy2

> What sort of fence was the Melbourne one ? Temp fences don't count. They get blown over every day. There is a big development happening at the Brisbane tennis centre and to advertise it theses clowns got a full on steel structure about 4 mt x 4 mt and about 4 mt in the air ( on posts). The post holes looked to be about 600x350 based on the concrete attached to the posts as the complete structure lay smashed on the ground 2 days after installation.

  Melbourne? 
40 year old 3m high brick wall - some numpty decided to put a 3m high sign on the top of it attached to the wall  (so doubled the area on an already shaky wall)- brought the whole lot down in a >100kmh gust.  Got fined a qtr of a million for abject stupidity

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## r3nov8or

Melbourne > Grocon ordered to pay $250,000 fine for Carlton wall collapse which killed three - ABC News (Australian Broadcasting Corporation) 
Think 'Aussie Signs' also got fined the same

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## DuckCommander

> Bwahahaha. Not at all. Cast 600 mm high winds in line with the blocks and bolt a hardwood post with 2 xM12's and there is no way that wind load will move it. Absolutely no way. It might wobble a bit if the posts were 2 mt high with zero gaps in the pickets bit I believe it's not a big fence and it will be pickets. I would be more concerned with the integrity of the block wall than the fence sitting on top of it.

  Again you are just giving your opinion on using something that's not designed for those loads. Wind loads, even on a picket fence, can be significant. I can tell you your brackets have bugger all bending capacity. I have seen a muppet use them in my area for this very same purpose and guess what... It failed fairly impressively on a very windy night. So as you say "Absolutely no way", I'm telling you you're wrong. I'm sure you will rebut with some more opinion as you seem to be full of it.

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## intertd6

> What sort of fence was the Melbourne one ? Temp fences don't count. They get blown over every day. There is a big development happening at the Brisbane tennis centre and to advertise it theses clowns got a full on steel structure about 4 mt x 4 mt and about 4 mt in the air ( on posts). The post holes looked to be about 600x350 based on the concrete attached to the posts as the complete structure lay smashed on the ground 2 days after installation.

   The moral of the story is nobody should be guessing when it comes down to safe design, especially when the general public can be impacted upon. In this case it's unknown the type & size of block being used, the size of the footing, the strength of the core filling, or whether the wall is reinforced & designed by an engineer, all we know is that the wall is core filled which means if unreinforced it could be vertually be kicked over.
inter

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## ringtail

That's true. Hopefully the OP can shed some light on the wall design.

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## r3nov8or

I agreed in post #7  :Smilie:

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## ringtail

> Again you are just giving your opinion on using something that's not designed for those loads. Wind loads, even on a picket fence, can be significant. I can tell you your brackets have bugger all bending capacity. I have seen a muppet use them in my area for this very same purpose and guess what... It failed fairly impressively on a very windy night. So as you say "Absolutely no way", I'm telling you you're wrong. I'm sure you will rebut with some more opinion as you seem to be full of it.

  Full of opinion but more importantly, full of real world building experience which is something you obviously have none of. Feel free to join the list of haters though. Give me evidence of the force needed to yield 50x5 flat bar on edge ? Then give me the moment force to yield 50x5 flat bar on edge. Then give me the force to yield 2 x 50 x 5 flat bar on edge with 100x100 HWD sandwiched between with 2 x M12 bolts. You must provide this evidence in some form of engineering document. Then give me the force required to yield 5 complete assemblies simultaneously. I picked 5 but it could be 3,4,6,8 depends on how many posts the OP intends to use. Good luck, I'll be waiting. Oh, I also want the address of the failure. Since it's in Brisbane I can go around and verify.

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## Marc

Well, here is my opinion: Demolish the Block wall. Dig a trench 800x800 all along the fence and fill with concrete. Have 4 16mm galvanised reo sticking out of the footings every meter. Add columns to the desired height using formwork 400x400. Attach the picket fence to this using stainless steel 16mm bolts ...  :Smilie:  
PS
I suggest using cast iron pickets. 
On second thought ... nee, do nothing of the sort, just pour the whole height in concrete and paint the pickets on it.

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## ringtail

Just go a tilt slab fence Marc.  :Tongue:

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## Marc

Well, a 400 mm concrete wall made with the right mix and steel, can take 50 mm shells for a considerable lenght of time, so ... that must be worth something!

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## ringtail

Have you upset the neighbours again ?

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## intertd6

> Well, a 400 mm concrete wall made with the right mix and steel, can take 50 mm shells for a considerable lenght of time, so ... that must be worth something!

  i was on a project that had 500mm thick RC concrete walls with 2 layers of n20 bars @ 200cts that wasn't watertight, I wouldn't be standing behind any wall those clowns made in any wind, let alone sheltering from fire.
inter

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## Marc

What was the question again?  :Smilie:

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## DuckCommander

> Full of opinion but more importantly, full of real world building experience which is something you obviously have none of. Feel free to join the list of haters though. Give me evidence of the force needed to yield 50x5 flat bar on edge ? Then give me the moment force to yield 50x5 flat bar on edge. Then give me the force to yield 2 x 50 x 5 flat bar on edge with 100x100 HWD sandwiched between with 2 x M12 bolts. You must provide this evidence in some form of engineering document. Then give me the force required to yield 5 complete assemblies simultaneously. I picked 5 but it could be 3,4,6,8 depends on how many posts the OP intends to use. Good luck, I'll be waiting. Oh, I also want the address of the failure. Since it's in Brisbane I can go around and verify.

  Too much time on your hands mate? You trying to be a posting grandmaster or something?
I've plenty of "real world" building experience and judging by your posting here and elsewhere, more rounded than you.
Your evidence demands are ambiguous at best and demonstrate you've heard a few things in the past but don't have a grasp on the actual meaning nor ability to calculate.
Address of the failure? Mate who do you think you are? An authority of all things building? I can assure the fence was replaced two years ago and no longer remains in ruin.
Get off your high horse.

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## ringtail

So in other words, you have no proof and are unable to provide any data to support your claims. Of course, being the "posting grandmaster" that I am I always new this would be the case. I suspect what you know and what you think you know, particularly when it comes to steel, are worlds apart. Nice try though. Maybe if you had been here since 2009 you would be a "posting grandmaster" too.

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## Marc



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## DuckCommander

No proof and no data? You've provided nothing to go on. "force needed to yield 50x5 flat bar on edge"... This statement makes no sense. A force applied how? Are you confused with stress? Do you know the difference? How and where is your force being applied? How is the flat bar restrained? What are the connections?
"moment force to yield 50x5 flat bar on edge" makes as much sense as your first comment, none, without further info.
"force to yield 2 x 50 blah blah blah" AGAIN, you do not understand what you are asking. What force? Where's it being applied? This is basic 101 stuff you are not comprehending.
Stick to your decks and whatever else it is you do, leave the engineering and math to others as you're embarrassing yourself.
(I've less than 70 posts per year, you in excess of 900, keep trying sunshine)

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## ringtail

Oh dear me. We are talking high wind stirrups DC. Had you forgotten ? They are made with 50x5 flat bar. Now, if one was to cast them into the wall and in line with the wall ( bolts running parallel to the wall) then the 50 x 5 would be on edge. It's a technical term DC, try to keep up. So with the stirrups cast into the wall as mentioned, with the posts mounted in the stirrups with 2 x M12 bolts as per industry standards my question to you was and still is ; how much force ( yes force in kn, from wind - as is your argument) is required to get that 50x5 flat bar to yield ( another technical term, look it up)  so that 1 fence post falls over. My other question to you was and still is ; given the number of posts required is unknown, lets say 5, how much force in kn, from wind, is required to yield all five ( or however many) stirrups simultaneously. My third question to you was and still is ; what is the moment force, in kn, from wind, required to yield the steel. Now if you don't understand basic engineering terminology, particularly relating to steel, that's fine. Just say so or google it.

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## DuckCommander

You are not an engineer and clearly have no grasp on this subject. 
You DO NOT understand force and pressure.
You DO NOT understand moments, lever arms, or basic statics. 
Through lack of understanding, you HAVE NOT given the basic information to calculate what you are demanding.
You HAVE NOT given any indication of understanding of material properties like yield stress of the steel.
You have shown you do not comprehend joint mechanics. 
You are asking for a kN load to yield a cantilevered post. Where is this magical load being applied? You do not understand the mechanics at all. Do you understand that the location of the applied force in kN is the FIRST thing you need to know and NOTHING can be calculated without it? It proves you HAVE NO IDEA. 
Your second question is just as laughable as your first question. You ask for force in kN (I'll address the kN below) to yield 5 posts. Well lets do some simple math for you... 5 x (that "x" stands for multiply) [kN to yield one post]. The question is useless in engineering terms here. Are you trying to say you need 5 times the wind load to yield 5 fence posts?  
Your third question is just the icing on the cake... You ask for a "moment force in kN". Mate perhaps you better google that before replying. Moments ARE NOT a kN force! It's very basic mate... Moments are kilonewton metre (kNm). Big difference mate. I wouldn't hire a graduate who got that wrong.  
Your third question I can actually do something with in the material property sense if I ignore your lack of understanding and make some assumptions, but even with the answer you wouldn't know what it means...
"moment force to yield a 50x5 flat bar on edge" (correct terminology is about the major x axis, google it) 
Moment = stress x section modulus (big words I know you will have to google it)
section modulus = bd^2/6 = 2083 mm^3
yield stress [assumed]= 250 MPa (N/mm^2 if you're confused) 
Moment = 0.5 kNm (take note of units, I skipped a step there, you may get confused)
Now since you do not know what this means I will break it down for you a little more. 
Fence is 1.3m high and 2.4m post spacing and no gap palings. Post tributary width (google the term) is 2.4m. Assuming uniform loading (w) and a low wind load of 1kPa, we have w=2.4kN/m.
The moment for this loading case is M = WL/2 where W = w x L. 
Therefore, M = 2.0 kNm
That's a magnitude of 4 fold overloaded. 
Easily overcome, but you wouldn't know how to do it economically just by looking at the formulas above. 
Stop embarrassing yourself ringtail. You clearly have no idea what you're talking about. I deal with your type regularly (builders who think they can engineer), you know a thing there and a thing here, but really you don't know how it works, to the point you are dangerous, much like your average punter who does their own electrical work. 
I eagerly await your response, no doubt chasing your tail to save face and probably using words and concepts you don't understand.

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## johnc

I reckon this has gone on enough, I don't think I would be that keen to bolt a fence onto a block wall unless it was core filled with bar into the footings least it fall over under wind load (giving way along the mortar line). Equally I'm not an engineer but "it is just a fence FFS" doesn't really cut it either. Duck Commander and others make a valid point, a fence failing can kill or maim, near enough isn't good enough and maybe this particular wall isn't suited to a fence being mounted on top.

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## Marc

> Cast in fin plate into blocks with min 2 bolt to timber post connection with large ie 200mm spacing between bolts. Long axis of fin plate perpendicular to fence direction. Both you're proposed options I would not consider adequate as a high wind brackets are not designed for bending loads (wind on fence) just uplift. Timber cast in concrete is not a durable connection.

  So what is your adequate solution? Fin plate? What size? How deep in the block wall? If the wind can brake a high wind stirrup that by the way is 2 50x5mm then it would topple the block wall with the fence, no point making the link between fence and wall stronger than the wall itself. The most sensible solution is from R3nov8r, run the post in the ground forget the wall.  
By the way a display of 'googleable' terms and formulas means nothing at all. 
What was that joke bout the engineer again? "What you said is true but useless" 
A sensible observation about the use of high wind stirrups would have been that the bolts are too close to each other and so the post would probably break at that point way before the stirrup bends.

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## r3nov8or

> ... The most sensible solution is from R3nov8r, ...

   I'm finding this is happening a lot   :Smilie:

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## Marc

Now now, don't push you luck I still like my bunker fence that takes 50 mm shells  :Rofl5:

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## DuckCommander

> So what is your adequate solution? Fin plate? What size? How deep in the block wall? If the wind can brake a high wind stirrup that by the way is 2 50x5mm then it would topple the block wall with the fence, no point making the link between fence and wall stronger than the wall itself. The most sensible solution is from R3nov8r, run the post in the ground forget the wall.  
> By the way a display of 'googleable' terms and formulas means nothing at all. 
> What was that joke bout the engineer again? "What you said is true but useless" 
> A sensible observation about the use of high wind stirrups would have been that the bolts are too close to each other and so the post would probably break at that point way before the stirrup bends.

  I was addressing the first issue of the load path, logically. Are you asking me for a design? Do you think an engineer wouldn't see the other obvious issues? 
The block wall is very easy to address. I read from the OP that it is not yet constructed. If such the case I would run a couple extra vertical bars at each post location to footing if its required. The connection style would be dependent on what the application/look was to be. By the formulas given increase of the breadth of the fin plate gives small return, increasing the depth gives a square root return on strength. So a deeper, slighty broader, double or single fin plate. 
If the wall is already built and wall reinforcement unknown, then post to ground is better. If wall isn't built, its uneconomical and probably ugly. 
I'm not sure what you're googling, plenty of stuff out there. It's understandable if it's confusing as you likely haven't been to uni to learn first principles and all that. 
This joke.. never heard it mate. If you think building safe buildings, bridges, planes etc etc is useless, then go be a cave man.

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## ringtail

DC, you have as much info as I have. We know the fence might be 1300 high. We don't know how long it is, we dont know how many posts there are, we maybe know it's a picket fence, we don't know if there are gaps between the pickets and we don't know the orientation of the fence in relation to the prevailing wind or the direction of the expected destructive wind load. We do know that you dispute the ability of the high wind stirrup to resist wind loads that could potentially be applied to the fence. So let's start again, without the personal insults. I'm genuinely interested in knowing the figures as you see them. So, as wind load is the factor, this is what I want to know.  
1. What is the force required to yield (beyond elasticity) the 50x5 flat bar steel that the stirrups are made from assuming the fulrum length is 1300 ? So assume the stirrup is immovable and it has a 1300 long lever fixed to it. Force is applied to rotate the  steel around its x axis. Express the force required as wind speed if possible. ie, 100, 160 km/hr
2. what is the sustained AND gust wind speed required rotate the complete fence, assuming at least 5 post assemblies are used and assuming the fence posts are 1300 high, again around its x axis.  
3. Will the timber posts fail before the steel  and if so, what are the sustained and gust windspeeds required to achieve this ?  
I agree with you that stirrups are designed to prevent uplift but that doesn't mean they can't be used for other applications. I believe this is a totally valid application for this sized fence. You obviously believe otherwise so all I want from you is the proof.

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## Marc

> I was addressing the first issue of the load path, logically. Are you asking me for a design? Do you think an engineer wouldn't see the other obvious issues? 
> The block wall is very easy to address. I read from the OP that it is not yet constructed. If such the case I would run a couple extra vertical bars at each post location to footing if its required. The connection style would be dependent on what the application/look was to be. By the formulas given increase of the breadth of the fin plate gives small return, increasing the depth gives a square root return on strength. So a deeper, slighty broader, double or single fin plate. 
> If the wall is already built and wall reinforcement unknown, then post to ground is better. If wall isn't built, its uneconomical and probably ugly. 
> I'm not sure what you're googling, plenty of stuff out there. It's understandable if it's confusing as you likely haven't been to uni to learn first principles and all that. 
> This joke.. never heard it mate. If you think building safe buildings, bridges, planes etc etc is useless, then go be a cave man.

  _I don't want anything, it is the OP that does, and he wants a practical answer not a lecture. Your replies are useless to him as they would to me or anyone else reading them. Your argument is only partly clearer now that I asked for more practical suggestions. As for your attempt at insulting me, your efforts are noted but you must do better than that._

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## OBBob

> I'm finding this is happening a lot

  Lol! I'm hoping there's going to be a movie because the reading has gotten too much.

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