# Forum Home Renovation Brickwork  Reinforcement for Retaining Walls & terminology

## scoobysteve

Hi All,  
i'm pretty new to concreting and blocklaying so if someone can help me out, it would be great. (i've got someone who knows what they're doing but I havent been able to chase him down just yet). 
Tomorrow i'm planning to duck by the local steel supplier and chase down some prices on reinforcement for my block retaining wall footing. 
However, is it as simple as ducking in and asking for reobars? 
I've got the boral guide here and looking at the footing design it lists N12 @ 400CRS and N16 @ 300CRS. 
I'm pretty sure that the N12 is 1/2 inch thus the N16 Would be 1/6 inch. However does the "N" stand for anything and also, what does the "400CRS" mean? 
Also,instead of asking for Y bars, would starter bars be the same? 
What about the mesh? is as simple as asking for mesh for concrete? i dont need to know a specific type? I think SL72 is a type. 
Lastly if i use mesh in my footings do i still need the horizontal bars in the footing as well - the boral guide doesnt list the mesh only about 6 horizontal bars in the footing. 
Lastly, can the starter bars go up to 1m high or are they set height? the reason why i ask is that i'm trying to eliminate the need for X bars.  
Sorry for all the questions, but any help before i duck into the steel shop will help as it will make sense of any terminology they throw at me.  
thanks in advance.

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## Gaza

see comments,
good luck  

> Hi All,  
> i'm pretty new to concreting and blocklaying so if someone can help me out, it would be great. (i've got someone who knows what they're doing but I havent been able to chase him down just yet). 
> Tomorrow i'm planning to duck by the local steel supplier and chase down some prices on reinforcement for my block retaining wall footing. 
> However, is it as simple as ducking in and asking for reobars? 
> I've got the boral guide here and looking at the footing design it lists N12 @ 400CRS and N16 @ 300CRS. 
> I'm pretty sure that the N12 is 1/2 inch thus the N16 Would be 1/6 inch. However does the "N" stand for anything and also, what does the "400CRS" mean? N12 = 12mm N16= 16mm  400CRS means you need to put the reo bars at 400mm centers, when you layout the postions you come in from one end so the first bar is in the middle of the hollow section of the block, then measure 400mm and so on from there.
> Also,instead of asking for Y bars, would starter bars be the same? 
> What about the mesh? is as simple as asking for mesh for concrete? i dont need to know a specific type? I think SL72 is a type.  SL72 is sheet mesh 72,  
> Lastly if i use mesh in my footings do i still need the horizontal bars in the footing as well - the boral guide doesnt list the mesh only about 6 horizontal bars in the footing. 
> ...

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## Batpig

Dear Scooby,  

> I'm pretty sure that the N12 is 1/2 inch thus the N16 Would be 1/6 inch. However does the "N" stand for anything and also, what does the "400CRS" mean?

  The numbers in question (as in "12" and "16") are actually the nominal diameters of the bars in millimetres. 
The letter "N" is simply a form of nomenclature that designates the reinforcement as belonging to a family of various sized bars whose strength and shape properties are stipulated in an Australian Standard that is used by Engineers. The reo shop will know exactly what you want when you say "N12" or "N16"... 
"400crs" means that the bars in question are required at spacings of 400mm to each other. My guess is that the N12's at 400crs are running parallel to the wall (and just there for shrinkage, and for tie-up with the N16's), while the N16's at 300crs will be at right-angles to the wall, and doing the main work of providing bending-strength to the footing.   

> Also,instead of asking for Y bars, would starter bars be the same?

  "Y" bars were actually the old version of the newer, stronger "N" bars. Is the design somehow asking for both? Anyhow, it's not a specific way of referring to Starter Bars, so the answer to your question is "no".   

> What about the mesh? Is it as simple as asking for mesh for concrete? i dont need to know a specific type? I think SL72 is a type.

  Well, there are different thicknesses of mesh that belong to the same "SL" family. You'd have to ask for the size that the design specified.   

> Lastly if i use mesh in my footings do i still need the horizontal bars in the footing as well - the boral guide doesnt list the mesh only about 6 horizontal bars in the footing.

  I'd say yes, you'd still need the horizontal bars, but instead of the mesh - rather than as well as it. N16's @ 300crs is fairly substantial reinforcement Scooby. I think you'd struggle to find a mesh that could replace it... 
Strang thing is, though, that if the N16's @ 300crs were the flexural reinforcement (being heavier than the N12's @ 400crs), there will be problems trying to get the Starter Bars to line up with the centres of alternative cores in the blockwork. You'd better double check your drawing.   

> Lastly, can the starter bars go up to 1m high or are they set height? the reason why i ask is that i'm trying to eliminate the need for X bars.

  They can go as high as you practically want them to go, but not any lower than the design specifies, because they need to lap with the reinforcing bars in the blockwork by a certain amount in order to transfer tensile stress from one to the other. The only thing is - what exactly do you mean when you say that you want to get rid of the X bars? Do you mean the horizontal bars in the blockwork, because you can't get rid of them - Nosiree!  :No:  (they're there for load-spreading and shrinkage-crack control...)
[/quote] 
I'd take the drawing with you when you go to the reo shop. 
Good Luck with it.
Batpig.

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## scoobysteve

Phew!!! thank god you guys replied.. i was way off. The N12 and N16 on boral guide actually lists them as horizontal support. 
I've attached the diagram to clear things up. You will see the x bar listed. 
Any more suggestions after viewing the diagram would be great.

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## Batpig

Dear Scooby, 
Ah huh! The "X" and "Y" references suddenly make sense. I should have been more on my toes than what I was... :Doh:  
Looks like I was wrong when I said that the N16's @ 300 would be the main flexural reinforcement, because they're clearly running along that footing, rather than across it. But the resulting cross-sectional area of steel may still be the amount required for anti-shrinkage in the footing, because the footing is fairly thick, and there's only one layer of reo. You will notice that the longtitudinal bars in the blockwork are down to N12's at 400, but then again - the wall is only 140mm thick... 
In a couple of ways, the design is unusual. Firstly - unless things have changed, I was under the impression that the standard minimum surcharge to be catered for behind the wall was 5kPa, rather than just the 2.5kPa that is shown. Secondly, the top of the footing has a little "hob" in its shape - directly under the blockwork. That's going to be a "bugger" to form up. Are you sure that the drawing is a standard Boral design? 
Good Luck once again,
Batpig.

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## Metung

The Boral specification will give you one hell of a strong, expensive retaining wall. I don't know how high or long your wall is or what is behind it but keep in mind that there are lots of 600-800mm high retaining walls in suburban gardens that are simply made from brick or rocks grouted together and are doing the job quite adequately. Not suggesting you use that method, but if the wall is in that height range and depending on its length, then I would consider reducing the amount of reinforcement if the saving was going to be worthwhile.

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## Blocklayer

Also, be sure to spend the time to position the starters so they go in the centres of the block cores. With 140 wide blocks it's easy to get them wrong. The cores aren't very big.  
From the very end of the wall, assuming it starts with an uncut stretcher or half, make sure each starter is positioned to an odd measurement. eg: 100, 300, 500, 700, 900, 1100 etc. And 70mm in from the face. This will place them in the centre of the hollow cores. 
I've seen plenty of footings where the starters have been carefully placed, but all in the solid webs of the blocks. After they are all bent over and first course blocks cut to fit them, it can be a mess. 
:

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## scoobysteve

thanks for the input.. it definitely clears things up tremendously... and yes, the mate who is gonna help me out with this wall did mentioned that i wouldnt need as much reinforcement as per the diagram - thats gonna save a bit on costs as the steel is pretty dear.

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## Terrian

> I've got the boral guide here and looking at the footing design it lists N12 @ 400CRS and N16 @ 300CRS.

  I'm pretty sure that the N12 is 1/2 inch thus the N16 Would be 1/6 inch. However does the "N" stand for anything and also, what does the "400CRS" mean? [/quote] 
that would be 12mm & 16mm   

> What about the mesh? is as simple as asking for mesh for concrete? i dont need to know a specific type? I think SL72 is a type.

  SL is the type 7 is the thickness in mm 2 represents 200mm squares in the reo, but for footings you wont be using sheets of reo (2.4m x 6m) you will be wanting 3 bar or 4 bar trenchmesh 
Just how big is this wall you are wanting to build ?

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## scoobysteve

the wall will be 1m high for two walls (that are in parallel with each other). The main wall goes back another 0.8m from the front wall and rises 0.8m. 
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## GrahamC

Definitely make the starter bars go 1m high. Most of mine were - no issues for laying the blocks. You will save a heap on steel. Probably make them 50mm lower than the actual top though. 
You could consider filling the blocks as you go - filling 140mm blocks is nortoriously difficult once finished. 
I think it might be worth considering using 190mm blocks. You may even save on steel.

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## zacnelson

Do you have a link to the Boral document?  I may find it a helpful resource in the future. 
Thanks

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