"strength" of a standard concrete slab with UFH

[Tom]

Hello all, bit of a random question, can anyone advise on the "strength" of a standard floor slab with UFH. i.e what loading (in kg/sq metre?) is the minimum a floor should be able to take? Is there a building regs requirement? I'm imagining a standard sort of insulated slab with perhaps ring beam.

Apologies for the vagueness of the question, and I'm sure there are many if's and but's, but just a ballpark figure would be great.

Thanks all

Tom

[Conor]

standard would be C25 or C30 concrete mix. Would be either 100mm or 150mm thick with steel mesh about 50mm below the FFL. Ring beam would be a bit thicker with 12/14mm rebar and eps300 under it. All depends on your wall makeup and ground conditions.. Heavier the building, thicker and wider the ring beam needs to be. I'm looking at 900mm wide and 300mm thick for my ICF build. Rest of slab will be 100mm thick with just mesh and EPS100 under. With a timber building, you may not need anything more than just the 100mm/150mm thick raft. 

 

Ensure slab is properly protected from temperature extremes during the curing process to prevent cracking if it's your finished floor.

Edited October 13, 2019 by Conor

[Jeremy Harris]

I have a feeling that floor loadings are now all in one or other of the Eurocodes (don't have that one to hand).  IIRC, Part A just references Eurocodes for various floor construction methods.

 

In practical terms, our 100mm thick slab, that has A142 steel fabric in the centre, UFH pipes tied to this, and uses C30 concrete, is compliant.

[Tom]

Thanks both, so is it possible to put a figure on the "strength" of the floor? E.g. must withstand x kg/ m2?

[Conor]

14 minutes ago, Tom said:

Thanks both, so is it possible to put a figure on the "strength" of the floor? E.g. must withstand x kg/ m2?

Doesn't really work like that. Yes, you have to calculate how much static and live load a part of a structure must support. E.g. for a floor span in a residential setting, it would be in the region of 3kn/m² . But for foundations and a floor slab, the job is to transfer the building loadings safely to the ground below. So it's not just compressive strength of the concrete. 

[PeterW]

14 hours ago, Tom said:

Thanks both, so is it possible to put a figure on the "strength" of the floor? E.g. must withstand x kg/ m2?

It’s really difficult to calculate as whilst the slab acts as a beam for engineering purposes, the loads are not transferred to the edges and essentially a “normal” slab just has to support self weight plus normal loading which is likely no more than 0.5kN/m² 
 

If you start adding point loads such as piers or load bearing walls then it changes the game. Likewise, use an insulated slab and apply a thickened edge and then wall and roof loads to it and it’s a whole new world !!

 

For pure reference, a non reinforced slab under normal loading of 100kN/m2 will span D/50 with 100% failure tolerance, so a 100mm slab will support a load over a 2m span without failure. 

Edited October 14, 2019 by PeterW
corrected the typos..!

[Ed Davies]

11 hours ago, PeterW said:

which is likely no more than 0.5Kn/m2. 

 

kN. SI prefixes for x1000 and below are lower case, symbols for units named after people (Sir Isaac here) are initial capped.

 

I always find these quoted floor loadings surprisingly low. E.g., a rack of bookshelves could easily weigh 3.6 kN per linear metre. Assuming that's spread over a metre each side (2m span) it's still 1.8 kN/m². Or, clicking on the first washing machine on the Argos site, mass is 66.5 kg, width 60cm and depth 52cm so the floor loading is 66.5 * 9.81 / (.6 * .52) = 2.091 kN/m². OK, it'll be spread over a bit more area but there are probably other heavy things near it plus the dynamic loads as it tries to shake itself to bits, as is the wont of such things.

 

[PeterW]

1 hour ago, Ed Davies said:

 

kN. SI prefixes for x1000 and below are lower case, symbols for units named after people (Sir Isaac here) are initial capped.

 

I always find these quoted floor loadings surprisingly low. E.g., a rack of bookshelves could easily weigh 3.6 kN per linear metre. Assuming that's spread over a metre each side (2m span) it's still 1.8 kN/m². Or, clicking on the first washing machine on the Argos site, mass is 66.5 kg, width 60cm and depth 52cm so the floor loading is 66.5 * 9.81 / (.6 * .52) = 2.091 kN/m². OK, it'll be spread over a bit more area but there are probably other heavy things near it plus the dynamic loads as it tries to shake itself to bits, as is the wont of such things.

 

 

Apologies - this is the joy of typing on an iPhone and letting it autocorrect !! Have now corrected, and also added the right loadings..!