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Author Topic: in slab ufh point loading capacity?  (Read 4509 times)
Gareth J
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« on: January 20, 2020, 10:47:13 AM »

I'm rebuilding an outbuilding as a utility/studio. Currently leaning towards wet, in slab UFH, obviously insulated underneath.

My current concern is that we might want to put a pretty dense bit of ancient machinery in there. Maybe 1-2 tonnes on a footprint of 1-2 square foot.

Just wondering if there were any sensible resources to look at the loading capacities of different thickness slabs?

At this stage, specifics are sketchy (including the fact that the bit of kit we are concerned about doesn't exist yet).

Any thoughts appreciated, thanks in advance!
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marshman
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« Reply #1 on: January 20, 2020, 11:02:00 AM »

is the base flat so the load is spread evenly or is it on pads say on each corner? Makes a difference!

If it were me I would work out where I wanted to place it and thicken up and reinforce the slab/screed locally and run the UFH around that area. This is assuming you go for a fairly thin screed - 50mm or so. Much thicker and the response time becomes very slow, ok for 24/7 occupation but if it is a 9-5, 75 days a week work/studio that may not be ideal. Also bear in mind a standard screed mix is no where near as strong as a concrete mix for a normal oversite.

Roger
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Nickel2
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« Reply #2 on: January 20, 2020, 11:33:08 AM »

What had you in mind for ye 2 tons per square foot of ancient machinery? Drop-hammer? Anvil? (visions of centrally-heated blacksmith's forge) My workshop floor is a 6" steel mesh fabric reinforced slab base, then 2" of Jablite, surfaced with 3/4 shuttering ply. 2x2 battens provide fastening area.
I'm not a structural engineer, but just rolled in a bit of common-sense thinking.
Where the eight 4x2 bench-legs stand on the floor I have placed 6" noggins of 4x2 to transfer the potential load through the insulation, directly to the concrete below. I could  put over a ton on the bench without thinking about it.
My lathe (550kg, 1200lb) is mounted on two 7x4 longitudinal bearers, directly onto the insulated floor. This gives a floor-loading of about a pound per square inch, which is totally acceptable: The spec for my Jablite domestic floor insulation is about 3 1/2 pounds per square inch for 1% compression, so 3 1/2 times better than required.
I worked on the principle of looking at the maximum load specified on the area, then making the area big enough to carry an acceptable load whilst remaining within figures; i.e. spread the load.
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Gareth J
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« Reply #3 on: January 20, 2020, 12:11:07 PM »

It's for an old printing press. Like I say, seeing have one yet, but I'm keeping my ear to the ground. It would be pretty static so not pounding itself into the floor.  Could be on legs, but I'd be able to make a spreader plate easily.

I had considered building up a solid column of concrete, through the insulation but as the object and it's location are all a bit pie Inthe sky just yet, not straightforward.

Thanks for the input, definitely something worth putting more time to thinking about
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paul149
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« Reply #4 on: January 20, 2020, 03:42:59 PM »

If you bring the concrete up through the insulation then I think you might have a cold bridging/condensation problem if the room is heated.
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JohnS
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« Reply #5 on: January 20, 2020, 04:54:26 PM »

There is no point in having UFH under the printing press, so do not route any pipes where you intend it to be.

Consider the strongest screed you can get.  Talk to installers.  Perhaps use sand and cement with fibre reinforcement or concrete with smaller aggregate, eg pea shingle size.

Or mount the press on a 10 or 20mm steel plate to spread the load.  Feasible if it is only 1 or 2 sq ft.


PS it is incorrect to say that the ancient machinery does not exist yet.  It has to exist to become ancient.  You have just not found it yet.   fingers crossed!    wackoold
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marshman
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« Reply #6 on: January 20, 2020, 06:41:14 PM »

If you bring the concrete up through the insulation then I think you might have a cold bridging/condensation problem if the room is heated.

To be honest unless the property is built on permafrost I can't see cold bridging or condensation being an issue. The ground temperature under the floor is not the same as the outside temperature, so it is not the same as a cold bridge to an outside wall. I (well my wife has) a very large fish tank/aquarium mounted on two brick pillars which go through the insulated floor (UFH) directly onto the concrete oversite - for exactly the reasons quoted above, i.e. concern about the point load on the floor. I have just checked the temperature of the bricks at floor level - 17.5 deg C, floor temp is 21 deg C where the UFH is.Coldest surfaces in the room are the window frames at 14.5 deg C same as the external door panels in the room (both are modern uPVC triple glazed). Current room temp is 19 deg C, current outside temp is 4 deg C. So window frames are the coldest surface and never seen condensation on them. The glass measures 15 deg C but not sure about accuracy of the IR thermometer on a glass surface.

Roger
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Nickel2
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« Reply #7 on: January 20, 2020, 10:21:12 PM »

Another alternative would be to build a steel plinth. A trip down to the local welder/forge/fab-shop/scrappy could produce a meter/yard square bit of 10mm or 3/8" steel plate. (other thicknesses are available) A few quid's-worth of welding could make you a base for the stand.
1 ton on a square yard ~1 3/4 pound per square inch.
1000 kg on a square metre = 100 g per square cm. ~ 645 g per square inch ~ 1.4 pounds per square inch.
The actual slab will need to be able to carry the weight and not sink or tilt or split. A couple of shallow trench-beams with steel inside should prevent that.
Biff's yer man who knows most about building, so will soon put me in my place if I am talking rubbish... tomatosplat
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1.140kW mono south-facing at 49*
EpEver 4210A at 24v
New (Old) 8S7P LiFe battery, 105Ah @ 26.4V
EpEver STI1000-24-230 pure sine inverter
Of course it'll work. (It hasn't caught fire yet).
biff
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« Reply #8 on: January 21, 2020, 10:02:32 AM »

I am humbled N2,
                        But when they find out that all I did was make the tea, I could lose my lofty perch very quickly, Mind you, I used nothing but Lyons green label and Mr Kipling tea cakes.
    Getting back to the slab, well it would be a sin to pour the slab to carry 1 to 2 ton anywhere on it,s surface so it makes sense to go for support piers and cross beam.
  The slab can be poured the normal thickness for the span and the UFH pipes laid but accurately mapped. Then when it comes to installing the printing press, The correct measurements can be taken of the spreader plate and the Base for the piers poured, piers built and beam(s) set on padstones and squeezed up into position with steel plate,  The 170 x 100 beam can be U shaped, Already welded together or bolted together in situ.  The base for the piers could be 600 x 250 or a strip to that effect, The piers just concrete blocks  440 mm x 220 mm with a mortar mix of 4 to one sand and cement,,(no fairy liquid fight) The piers are 440 square , you cannot make a mistake in the bond Grin . When you get near the top, You stop 330mm from the underside of the slab, Then You put your padstone 300mm square x 150 on a nice tight bed, You should find that you have a good 10 mm clearance to push the beam into place . Then you take your 10mm steel plate and prising up the beam tight to the slab, hammer the 10mm plate home between the padstone and the underside of the beam.
   If the homework has been done carefully, The floor can be carefully broken through the insulation and scree to the slab, You can use solid oak pad coming up level with the finish floor and catching the spreader plate at the points of your choice.
  You can buy padstones already cured and hardened, Then all you have to do is allow 170mm + 10mm  from the top of the padstones to the underside of the slab.
   But of course you can only do it this way if you have access underneath,
                                  Biff
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Gareth J
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« Reply #9 on: January 21, 2020, 06:30:13 PM »

Thanks all! Well, just to play devils advocate, the press *may* not exist yet if I end up making it! but it'd be considerably less weight if I did. To the point I wouldn't worry about it.

I also wouldn't be concerned about cold bridging, yes, there would be a drop in performance but bearing in mind it'd connected to a slab with UFH in, if it got condensation on it, the windows would be streaming at that point.

Think the priority now has to be to actually get the press. Without it, I cant tell how heavy it would be, or even where it would need to go!

But it does seem that, if I'm at all concerned, a solid connection between top screed, through the insulation will help enormously. Even some strategically placed 4" cores drilled through the insulation and filled with good concrete mix to connect top screed and a foundation would probably be a good help. I can't say I fully follow biff's detailed reply but thanks for it, I'll read it through a few more times carefully.
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biff
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« Reply #10 on: January 21, 2020, 10:08:33 PM »

The fault is mine Gareth,
                      I just read through it and it is as clear as mud.
   I am assuming that the press will be located along a wall,   that the press will have a footprint roughly , very roughly, of 1800mm x 900mm but frankly, having googled printing presses and their different manufacturers, I was astounded to see the sizes of these machines and 10 to 12ft  x 4ft would not be an exaggeration,  So you would have to make a wooden template to mark the centers of your support piers  and an 170mm x 100mm RSJ on padstones would have to run the full length with smaller lengths going off at right angles to catch the load bearing points. So if the press is set up in sections then these short lengths will catch the press supports next to the wall on the inside.
       All you are doing is transferring the load to the piers underneath and the outside walls of the shed,, Your idea of using a 100mm core drill is a good one and instead of concrete , use a tanalised round oak pad ,set in the core and left slightly raised above the screed,,say 5mm. You could seal and varnish them to add to the look. They would also act as dampers and not grind away.
  I hope this helps, quite often my attempts to clear the thinking only further muddies the water. 
                                           Biff
   Padstones are just good strong mix of concrete with some hardner added and left to cure.. You could actually cast them i situ or make your own inside the shed out of little Bottomless boxes 300mm x 300mm x 150 with some 6mm bar added. Don,t forget you need a gap of 180 to slide the steel into place and then underpin it with the 10mm metal plate.
    This is the one way you could have confidence  that your slab could carry such a load in comfort.
       
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