Steel Mesh Calculations

[Field_of_Dreams]

Does anyone know of a decent UK mesh calculator?

My head is about to explode trying to work out how much I need and the most cost-effective way of doing it regarding what size sheets I buy and what gets cut on site.

 

I was hoping it was simple...but for me it is not.

It is an insulated raft that is 10500mm x 5550mm (internal size) and will have a slab depth of 250mm.

The SE has specified...(dont get me started!)

2 layer A393 TOP with extra layer of A393 on edges at 2M wide plus the required lapping. 50mm concrete cover. (3 mesh layers in total) 

1 layer A393 BOTTOM with extra layer of A393 on edges at 2M wide plus the required lapping. 50mm concrete cover. (2 mesh layers in total)

 

I believe the lapping would be 400mm min for A393.

Not sure how close to the EPS the mesh has to go either. I know it is meant to be close, but how close?

 

With all the overlap, I am wondering if there will be any space for concrete!

 

I am hoping there is someone out there who has a wonderful calculator...or just likes puzzles 🙂

Any help on this is truly appreciated.

 

Thanks

 

[Thorfun]

why are you second guessing your SE? you paid them for a reason and now to try and calculate it on your own is not wise in my opinion.

 

if you think it's over specced then hire a second SE for a second opinion. if someone on here gives you the information and something goes wrong who's to blame? the SE will have professional indemnity insurance to protect against issues.

[Mr Punter]

If you are concerned about mesh buildup, instead of lapping you could butt the sheets and join them with H10 splice bars.  Because the slab is fairly small you could then use the smaller merchant sheets of mesh, which are much easier to handle.  Ask the SE to confirm if this is acceptable and the lap required.

 

If the SE is doing the structural design for the whole house it may be better to just stick with them.  You could request that they omit a layer or downgrade to, say 252 mesh but I doubt it will make a huge difference in cost and they may not agree to do it.

 

[JohnMo]

I had my first set of structural engineering drawings and challenged lots.

 

Ask why so much mesh and the reasons for it, with supporting calculations in writing (email).  My wall rebar requirements almost all disappeared, apart from what looked sensible.

[Field_of_Dreams]

2 hours ago, Thorfun said:

why are you second guessing your SE? you paid them for a reason and now to try and calculate it on your own is not wise in my opinion.

 

if you think it's over specced then hire a second SE for a second opinion. if someone on here gives you the information and something goes wrong who's to blame? the SE will have professional indemnity insurance to protect against issues.

I'm not trying to recalculate what the SE said.

 

I am asking how to best work out how many sheets and what size will fit the spec from the SE. 

[Field_of_Dreams]

1 hour ago, Mr Punter said:

H10 splice bars

Thanks for the info!

 

Do you have a picture of this? Not sure what it is and a google search showed too many different things for me to be certain what was correct.

 

 

[Conor]

52 minutes ago, Field_of_Dreams said:

I'm not trying to recalculate what the SE said.

 

I am asking how to best work out how many sheets and what size will fit the spec from the SE. 

Is there not a mesh/bar schedule on the drawings? We just sent the drawings off the the supplier and it all arrived on the back of a lorry a week later. As our walls were also RC, we didn't need to use links or overlaps, the U shaped starter bars did that, so despite having three layers at the ring, was simple enough.

[Thorfun]

1 hour ago, Field_of_Dreams said:

I'm not trying to recalculate what the SE said.

 

I am asking how to best work out how many sheets and what size will fit the spec from the SE. 

fair enough! then I apologise. I misread your initial post.

[George]

1 hour ago, Field_of_Dreams said:

Thanks for the info!

 

Do you have a picture of this? Not sure what it is and a google search showed too many different things for me to be certain what was correct.

 

 

It's just short lengths of B10 (10mm diameter) bar. usually you overlap by 400mm, so a 800mm length of B10 to lap 400mm onto each sheet. I think it would be more fiddly than lapping sheets, but all reinforcement work is fiddly!

 

I have to say, speaking as a structural engineer, 3No layers of A393 in the top of a slab seems excessive. I didn't put that much into industrial warehouse slabs.

 

Is it on piles/vibro-stone columns or particularly poor ground?

[Tom]

We've got 4 layers of A393 in our 200mm slab!

[TonyT]

What about  fibres instead of steel?

 

Saves a lot of work!

[Field_of_Dreams]

4 hours ago, George said:

It's just short lengths of B10 (10mm diameter) bar. usually you overlap by 400mm, so a 800mm length of B10 to lap 400mm onto each sheet. I think it would be more fiddly than lapping sheets, but all reinforcement work is fiddly!

 

I have to say, speaking as a structural engineer, 3No layers of A393 in the top of a slab seems excessive. I didn't put that much into industrial warehouse slabs.

 

Is it on piles/vibro-stone columns or particularly poor ground?

thanks for the info. Do you run a B10 bar alongside each of the bars on the mesh?

 

The ground is medium/high plasticity clay and there are several large mature sycamores within 4M of the building. There was also a eucalyptus on the site that has been removed but also impacted on the design, according the SE.

[Field_of_Dreams]

5 hours ago, Conor said:

Is there not a mesh/bar schedule on the drawings? We just sent the drawings off the the supplier and it all arrived on the back of a lorry a week later. As our walls were also RC, we didn't need to use links or overlaps, the U shaped starter bars did that, so despite having three layers at the ring, was simple enough.

No schedule on the drawing and I have not sent the drawing to a mesh supplier yet…was trying to figure it out before I did that 🙂

The walls will be ICF but they are not linked to the slab via any steel. 

[Field_of_Dreams]

3 hours ago, TonyT said:

What about  fibres instead of steel?

Do you mean in the concrete?

I have not looked at this…anything specific I should be aware of?

[TonyT]

https://www.hanson.co.uk/en/ready-mixed-concrete/reinforced-concrete
 

 

im doing a job soon with it, it’s about £40 a cubic metre on top of the concrete price in my area at least so about £130 all in a cubic metre for C35.

[Chanmenie]

I’m doing the same, fibre reinforced ecFlow concrete, a little more per m3 but I saved £1k on rebar mesh, plus the time and hassle of fitting it.

http://www.easternconcrete.co.uk/wp-content/uploads/2018/07/GDA-443_EcFlow-Nov2017.pdf

 

[Mr Punter]

7 hours ago, Field_of_Dreams said:

Thanks for the info!

 

Do you have a picture of this? Not sure what it is and a google search showed too many different things for me to be certain what was correct.

 

This is just lengths of rebar probably 800mm-1000mm to tie the sheets of mesh together where they butt up, so each end of mesh has a 400mm-500 lap and they will be every 200mm along the mesh.  I am not sure that steel fibres will work for you.  They are not a direct replacement for steel mesh but if the SE considers it acceptable then fine.

[Conor]

15 hours ago, Field_of_Dreams said:

No schedule on the drawing and I have not sent the drawing to a mesh supplier yet…was trying to figure it out before I did that 🙂

The walls will be ICF but they are not linked to the slab via any steel. 

 

That sounds very wrong. What's the reason? The ICF walls will have vertical reinforcement bars and these should tie in to the foundation slab. By the sounds of the mesh requirements this is a substantial structure and I'm amazed there is nothing tieing the walls to the slab.

 

Here's our slab before the pour. Note the vertical bars at 200mm centres. It's a basement, but the standard would be a single bar every 1200mm for a single story.

 

 

Edited September 29, 2022 by Conor

[Field_of_Dreams]

20 hours ago, Conor said:

That sounds very wrong. What's the reason?

I never understood it, but the wall provider (isotex) said it was not needed for single story/my project. The super structure SE did not think it was necessary and neither did the slab SE.

I assume the superstructure SE would be the one to add it to the drawing and maybe it is his conversation with the block supplier that led him to not add it in…I don’t know, but will call him and ask.

 

There are bars in the walls but all run horizontal.

The amount of mesh is due to ground conditions and trees.

[markc]

24 minutes ago, Field_of_Dreams said:

I never understood it, but the wall provider (isotex) said it was not needed for single story/my project. The super structure SE did not think it was necessary and neither did the slab SE.

I assume the superstructure SE would be the one to add it to the drawing and maybe it is his conversation with the block supplier that led him to not add it in…I don’t know, but will call him and ask.

 

There are bars in the walls but all run horizontal.

The amount of mesh is due to ground conditions and trees.

If there will be no side load (back filling etc) then no reason to tie walls into slab. No different to brick/block