How to space two parallel reinforcement bars vertically?

[AartWessels]

Feeling a bit thick here. I'm working out what I will need for the steelwork for my foundations, and have a hard time understanding how to space the two parallel bars above one another. 

 

[Gus Potter]

  On 01/03/2025 at 20:54, AartWessels said:

Feeling a bit thick here.

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Nothing "thick" about your query. Good spot!

 

Check with your SE as they should have provided this dimension. It's important for both top and bottom bar.

 

Often on a raft found the top of the ring beam is in tension (hence the top bar) when we design for say soft spots or want to shed load (called partial fixity) from column point loadings for example.

 

The detail you see with the top bar is probably the SE making sure the corner of the building doesn't sink (critical desing case) with the weigh of the external leaf if there is a soft spot at the corner.

[IanR]

  On 01/03/2025 at 20:54, AartWessels said:

Feeling a bit thick here. I'm working out what I will need for the steelwork for my foundations, and have a hard time understanding how to space the two parallel bars above one another. 

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Tie in some short rebar pieces horizontally and vertically. Push the pieces a little way into the EPS. Spacing sufficient to keep the longitudinals robust for the pour.

 

Edited March 1 by IanR

[saveasteading]

You mean how, physically, to keep them in the right place while pouring? Once you know the dimensions.

 

Your SE should also tell you how much overlap of bars ( top of my head, it  is 40 x 12 = 480mm).

 

You can get plastic or voncrete spacers which you tie to the bottom rod.  They keep it off the bottom.

F rr the other one I suggest you pour the concrete up to that height and compact it, then lay the other rod, then complete the pour. Be sure to then mix through that surface to make it monolithic  just use a 2 x 2.

 

Alternatively you could poke some small rods across the space at the right height and wire the rod to them. The advantage is that nobody forgets. 

 

[AartWessels]

Poking some small rods across seems to make sense. 

I had been on a witch-hunt for spacers which would take 2 vertically spaced rods 😁

[Gus Potter]

  On 01/03/2025 at 23:00, IanR said:

Tie in some short rebar pieces horizontally and vertically. Push the pieces a little way into the EPS. Spacing sufficient to keep the longitudinals robust for the pour.

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No get this check by an SE.

 

@IanR and all. Please don't dish out this advice / suggestions without knowing about the design philosophy. I respectfully suggest that you need to know not least about rebar anchorage, bond length and how that changes depending on the embeded depth in the concrete even if giving general advice on rebar.

 

For all and at say @IanR there is some great general advice here on BH but a lot is contradictory when talking about raft / ground bearing slabs. The main reason is that the ground varies from site to site so needs a bespoke solution. It's not just the ground but often the slope of the ground and the water table.

 

Funnily for me as a designer it's not the concrete slab or the insulation it sits (Kore etc) on that is the hard part to design. The really hard part / that risks my PI insurance (and your house) is often how much you need to dig out below the slab or raft! This is where the main risk lies.. in the ground under the insulation.

 

 

 

 

 

 

 

[IanR]

  On 02/03/2025 at 01:07, Gus Potter said:

No get this check by an SE.

 

@IanR and all. Please don't dish out this advice / suggestions without knowing about the design philosophy.

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You're over thinking it.

[Gus Potter]

  On 02/03/2025 at 01:08, IanR said:

You're over thinking it.

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Why?

[AartWessels]

  On 02/03/2025 at 01:07, Gus Potter said:

No get this check by an SE.

 

@IanR and all. Please don't dish out this advice / suggestions without knowing about the design philosophy. I respectfully suggest that you need to know not least about rebar anchorage, bond length and how that changes depending on the embeded depth in the concrete even if giving general advice on rebar.

 

For all and at say @IanR there is some great general advice here on BH but a lot is contradictory when talking about raft / ground bearing slabs. The main reason is that the ground varies from site to site so needs a bespoke solution. It's not just the ground but often the slope of the ground and the water table.

 

Funnily for me as a designer it's not the concrete slab or the insulation it sits (Kore etc) on that is the hard part to design. The really hard part / that risks my PI insurance (and your house) is often how much you need to dig out below the slab or raft! This is where the main risk lies.. in the ground under the insulation.

 

 

 

 

 

 

 

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Thanks, I understand your concern and will propose this to the SE first. I do not see how there would be harm in this for the outer leaf beam.

 

The main doubt I have about using steel for it is that when you stick that in the insulation that you'll end up with an exposed end of steel. 

 

 

[ETC]

Make it up with links but check the spacing first. Might just be 40mm/50mm from top and bottom for minimum cover.

[saveasteading]

  On 02/03/2025 at 01:08, IanR said:

You're over thinking it.

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Not at all. Unless you can explain why the accurate position of the bars does not matter.  Perhaps they aren't necessary at all.

 

  On 02/03/2025 at 07:40, AartWessels said:

you'll end up with an exposed end of steel. 

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My thought was to cut the control bars 25mm wider than the internal width and wiggle them into the inner faces, both sides. Then they are not exposed.

 

But it's not a greatly thought out design, and I would have expected a 'system' to have a standard solution.

Spacer for the bottom and 2 layers is still my preference IF you can trust the builder or supervise....otherwise they will likely end on the bottom.

[AartWessels]

  On 02/03/2025 at 10:01, saveasteading said:

My thought was to cut the control bars 25mm wider than the internal width and wiggle them into the inner faces, both sides. Then they are not exposed.

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I get that, but the exterior part of that insulation is just a former and will be removed after the pour as far as I understand. 

 

So I guess your other suggestion is better, albeit a bit messy and indeed requiring lots of trust and/or oversight. 

[saveasteading]

  On 02/03/2025 at 10:50, AartWessels said:

the exterior part of that insulation is just a former and will be removed after the pour

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I didn't realise that.

It doesn't really matter. 

Steel needs water and oxygen to rust, so it won't reach the working bars.

[Iceverge]

  On 01/03/2025 at 23:09, saveasteading said:

rr the other one I suggest you pour the concrete up to that height and compact it, then lay the other rod, then complete the pour. Be sure to then mix through that surface to make it monolithic  just use a 2 x 2

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I've been pouring some 2.4m long  220x220mm concrete gate posts recently for the farm. 

 

I included 4no 12mm rebars inset about 40mm from each corner for strength. I racked my brain about a satisfactory method to hold them in place and settled on shoving in some bars from the sides of the form to support them until the concrete set and hammering them out again. 

 

I wouldn't have even imagined your method could work I assumed the bars would just settle out of place when i vibrated the forms ( AKA hitting with a lump of timber).

 

Its reminded me I need to seal the holes left by the supporting bars now. 

 

[IanR]

  On 02/03/2025 at 10:01, saveasteading said:

Not at all. Unless you can explain why the accurate position of the bars does not matter.  Perhaps they aren't necessary at all.

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Pretty sure everyone would agree the position of the rebar within the beam should be where the SE has shown it in his section, that's why the OP has opened this thread and I have contributed with a means of doing so. If you believe I have said something different you need to go back and re-read my post.

[Gus Potter]

  On 04/03/2025 at 09:58, IanR said:

I have said something different you need to go back and re-read my post.

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I have, good solution! Eating some humble pie at my end.

 

Hopefully still pals?