# Forum Home Renovation Sub Flooring  Deciphering footing plan

## Andy Mac

Hi there,
I am in the middle of putting up a portal frame, and have posted a query before about the hole- now sorted out.
My next question regards the engineer's drawing of the pier footing reinforcing. I'd be OK if I had a top or side view to work with!
Anyway it appears there are 4 lengths of thicker reo (N12) running parallel with the RHS, forming corners of a box, but what do the zig-zag lines represent- "ligs"? Thinner reo (R6) I realise, but does it form a continuous spiral running around the 4 verticals, or just a zig-zag on 1 side, 2 sides, or 4 maybe, meeting up with them?? And how, if at all, does that structure join the RHS? My only idea is the two N12 bent into a U, which are to be welded to the RHS must join it somehow. "Bend into footing" is the description, so maybe just hooked into place?
And what is the difference between N and R reo bar, is it critical? 
Thanks in advance!

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## Batpig

Dear Andy, 
It looks to me like he just wants some normal square Ligatures - made from R6 smooth bars bent around to form squares - tied around the outside of the four N12 deformed bars at 300mm spacings from each other. If he wanted a spiral-wound cage, there is no way that he wouldn't have specifically mentioned it... 
The main N12 deformed bars should be spaced at 300mm apart from each other when measured across the diagonal when looking down from above, and the R6 Ligs go around the outside of them to stop the N12 bars from being pushed outwards when the concrete starts building up inside them during the pour. The R6 Ligs should have a 70mm long hook in each of their two ends at one of the corners of the resulting cage.  
Normally, the spacing of Ligs in a column arrangement would be limited to the lesser of either the diameter of the column (450mm in your case), or 15 x the diameter of the main reinforcement (ie. 15 x 12mm = 180mm). I know that it's not a "column" per se in this case, but rather a footing, but the Ligs are mainly there in both cases to stop the vertical reinforcement from flexing outwards during the pour (and they won't wan't to come back into vertical later either, no sirree... :No: ) so it might be worth your while ringing the engineer and just asking him whether the 300mm spacing was definitely what he wanted, and not 180mm. 
Don't worry about the post not being connected to the reinforcing cage. That post is going Nowhere without the concrete (and very slowly at that!) thanks to it's almost-full length embedment in the concrete, the 500mm-long N12 "whiskers" that will be welded to it, and the welded plate on the end. It can't go sideways either, because the concrete inside the cage will be virtually unbustable. If the whole thing is setup and poured correctly, that post 'aint going anywhere without the footing still around it. The cage and the post are kept separate during the pour to make it easier to get the post perfectly level and at the correct height, because your footing might not have been dug perfectly vertical. 
There is most certainly a difference between "N" and "R" type reinforcement. "N" is much higher strength than "R", and "deformed" (ie. Ribbed) in order to properly "develop" it's extra strength within the concrete. By comparison, "R" is just smooth. Having said that, though, don't just go and use any old wire for your Ligs - they have to be made from certified R-grade bar. You'll have to buy both types from a proper supplier of reinforcement. 
Make sure you use the proper 25MPa concrete, because the 20MPa stuff that they normally send out for residential footings is absolute krap, and not much better than just sweepings off the floor of the plant. If you're going to do the pour yourself, don't throw it all down the hole in one big go. Put just a bit down the bottom until you can accurately position the bottoms of the cage and the post, and then carefully pour the rest. You'll have to vibrate it or at least rod it as you go to eliminate voids and "folds" in the concrete. Maybe the Engineer can give you some tips... 
I think that covers what you wanted to know... 
Best Wishes and Good Luck,
Batpig.

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## Andy Mac

> Dear Andy, 
> It looks to me like he just wants some normal square Ligatures - made from R6 smooth bars bent around to form squares - tied around the outside of the four N12 deformed bars at 300mm spacings from each other. If he wanted a spiral-wound cage, there is no way that he wouldn't have specifically mentioned it... 
> The main N12 deformed bars should be spaced at 300mm apart from each other when measured across the diagonal when looking down from above, and the R6 Ligs go around the outside of them to stop the N12 bars from being pushed outwards when the concrete starts building up inside them during the pour. The R6 Ligs should have a 70mm long hook in each of their two ends at one of the corners of the resulting cage.  
> Normally, the spacing of Ligs in a column arrangement would be limited to the lesser of either the diameter of the column (450mm in your case), or 15 x the diameter of the main reinforcement (ie. 15 x 12mm = 180mm). I know that it's not a "column" per se in this case, but rather a footing, but the Ligs are mainly there in both cases to stop the vertical reinforcement from flexing outwards during the pour (and they won't wan't to come back into vertical later either, no sirree...) so it might be worth your while ringing the engineer and just asking him whether the 300mm spacing was definitely what he wanted, and not 180mm. 
> Don't worry about the post not being connected to the reinforcing cage. That post is going Nowhere without the concrete (and very slowly at that!) thanks to it's almost-full length embedment in the concrete, the 500mm-long N12 "whiskers" that will be welded to it, and the welded plate on the end. It can't go sideways either, because the concrete inside the cage will be virtually unbustable. If the whole thing is setup and poured correctly, that post 'aint going anywhere without the footing still around it. The cage and the post are kept separate during the pour to make it easier to get the post perfectly level and at the correct height, because your footing might not have been dug perfectly vertical. 
> There is most certainly a difference between "N" and "R" type reinforcement. "N" is much higher strength than "R", and "deformed" (ie. Ribbed) in order to properly "develop" it's extra strength within the concrete. By comparison, "R" is just smooth. Having said that, though, don't just go and use any old wire for your Ligs - they have to be made from certified R-grade bar. You'll have to buy both types from a proper supplier of reinforcement. 
> Make sure you use the proper 25MPa concrete, because the 20MPa stuff that they normally send out for residential footings is absolute krap, and not much better than just sweepings off the floor of the plant. If you're going to do the pour yourself, don't throw it all down the hole in one big go. Put just a bit down the bottom until you can accurately position the bottoms of the cage and the post, and then carefully pour the rest. You'll have to vibrate it or at least rod it as you go to eliminate voids and "folds" in the concrete. Maybe the Engineer can give you some tips... 
> I think that covers what you wanted to know... 
> Best Wishes and Good Luck,
> Batpig.

  I thank you sir for your detailed and informative answer, covers everything I needed to know! :2thumbsup:  Isn't this a wonderful place to come with a question! 
Cheers,

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## Andy Mac

I have just spent a day (finally :Redface: ) putting the cages together and into the holes...which of course needed to be redug again!  Sounds easy except for pulling out the two 150x50x 4.5m posts, then dropping them back in, underneath a roof :Eek:  
I bent the 6mm reo bar into zig-zags, using this bender I knocked together from scrap. I wired them together around the corner bars using stainless steel lockwire. 
Cheers,

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