Foundation under machine

Next year I will get a milling machine. I am aiming at something rather professional of weight in range of 1 ton, vertical and horizontal spindle, cooling system and power feed in both X and Y axis, with DRO but not a CNC.

Machine will be housed in unused room on ground floor of my property, about 170 square feet.

How such a machine should be bedded? There is a cocrete fllor there, about 2 or 2 1/2 inch thick. Under this is 3 inches of polystyrene foam, 6 inches of weaker concrete and then sand and soil.

I am concerned about polystyrene bit. IMO it will tend to sag under weight of machine, concrete floor may well crack and in any case I will not be able to level this machine proper. Simple idea is to dig out offending polysterene, fit steel construction matching stand of the machine and bed it on it. Or should I pour thick reinforced concrete square, say 4 x 4 feet, about 15 inch deep?

Any other ideas?

A quick google shows this and you will need to check it's right

According to BS6399-1, 1996 (Loading for buildings) a residential structure should be designed for a distributed load of 1.5kN/m2

So call that 150kg/m2

So a steel plate bigger than 6.6m2 under your machine will get the distributed load within the design limits.

If this is correct then yes you probably need to do something with the floor.

How are you going to get the machine in there?

regards Martin

I dont think I'd be sitting a ton of machinery with a relatively small base on concrete 2" thick, sitting on polystyrene.

Sounds like it is a room in your house, so I would think a professional builder's advice would be appropriate.

That is a minimum requirement for a floor, if you take a look at one of the popular insulations makes such as jablite then for their lowest density board that has a design load of 20kpa or 20kN/m2 or about 2 ton/m2

The top 2" will be screed not concrete

Edited By JasonB on 21/12/2017 11:36:15

Spread the load, perhaps a sheet of 1" Blockboard would do it? The machine will have 4 places on it's base where pressure is greatest, then 2 strips of 1/2" alloy 6" wide about 24" long on the blockboard would suffice.

Martin,

If you work out the floor loading over the full contact footprint of the machine I think you will be quite surprised at how low it actually is in terms of pounds per square inch.

Before we were allowed to start building, I had to quote the ground loading of a 5 foot 6 inch high dry stone wall to the National Trust structural engineer at Fountains Abbey 7 years ago, he was concerned that concrete foundations would be needed below it.

It worked out at no more than that under the foot of a 15 stone man building it and he went away quite happy with my assertion that all the ground preparation needed was to remove the turf layer and build straight off the subsoil. Traditionally these walls settle slightly as the ground below it compacts slightly and left undisturbed, such walls will stand straight and true for well in excess of 100 years.

Dry stone walls of that height have a weight in excess of 1 tonne per metre run, on a base that is 28/30 inches wide. As it happens I was visiting the place yesterday for lunch and a walk round with my wife, that particular wall is as straight as a die, just as it was when we finished it

As another example, there is a road bridge [in Norway I think] that is built on polystyrene blocks, how unlikely is that!

Regards Brian

Edited By Brian Wood on 21/12/2017 11:53:06

A simple test is to stand 10kg on a 100mm x 100mm bit of poly and see if that crushes which I doubt it will.

I'd get half a road plate and set that onto the floor with suitable tile adhesive and then stand machine on that which will spread the load over the required 1m2.

I know of someone who has a Bridgeport on a beam and block domestic floor with no issues

Martin,

How old is the floor - any ideas? It might give us some clues as to it's capabilities. From your description, and assuming it's an old floor, it sounds as though it may have been subject to an attempt to improve it's insulation levels at some time.

By way of background, the basis of design for domestic floors has been that they should be able to support a uniformly distributed superimposed load (in old imperial terms) of 30lbs/sq.ft. Your 1 ton machine would therefore need to be supported over 75 sqft to achieve that but as machine base bottoms are generally thinner edges of castings you'll probably be dealing with a much smaller contact area and therefore proportionately higher load/sqft at the contact with the floor surface.

That gives you the problem of deciding whether or not this is a practicable proposition. It might be achievable by spreading the load over a bigger area using something like a steel boiler plate spreader over the floor surface, or (provided it's economical) rebuilding the floor structure to suit the higher loads. Your existing 2 - 2 1/2 inches of floor is probably a screed rather than structural floor and the compressive strength of the polystyrene is an unknown factor but likely to be very limited; the 6 inch concrete slab is of unknown compressive strength so again you can't rely on it unless you can verify it's loadbearing capacity. By comparison a good reinforced concrete 6 inch floor slab would cope with the load but would need to be specifically designed for the job. Excavating and putting in a deep base as you describe might be possible, but you need to consider the effect of excavation close to foundations of adjacent walls.

The other factor you need to bear in mind is that any structural/insulation changes to the floor require prior approval under the Building Regulations so a chat to your local Building Control Officer at the Council would save you a lot of problems.

Sounds like it is a fairly modern house built to somewhere near current building regs. Digging up the floor to remove insulation will likely destroy the integrity of the damp proof course and could cause problems with damp in the future. May also make resale of the property difficult. Is also likely to breach current building regs.

How about casting a new reinforced concrete slab about 4" thick on top of the foor big enough to spread the load. If the slab is laid on a DPC plastic sheet should be fairly easy to remove if necessary.

John

As Journeyman says that is recent construction method so less than 30yrs old, last 10yrs would more likely be celotex/kingspan rather than polystyrene

I assume that the polystyrene layer is for insulation, I am surprised its on top of the load bearing slab, 2 to 2.5" of screed(?) will have no strength in this context. Were building regulations consulted before the floor was laid? When I extended my house, admittedly nearly 30 years ago, insulation requirements had been extensively upgraded. The floor had to consist of 50mm insulation, the DP membrane, 100mm of concrete (load bearing) then 50mm of screed. Unless regulations have changed over the years then it seems to me the floor has not been constructed properly.

Part of the extension to the house is the workshop, so I (discretely) increased the load bearing layer to 150mm and slipped in some reinforcement in anticipation of heavier equipment arriving, which it did!

John

Again I will say it. This is standard building practice slab or beam and block, layer of insulation, screed.

Simple example that your mill will not fall to the ctr of the earth.

Job I'm working on at the moment has this type of floor construction though celotex insulation and UFH clipped to that and screed over the lot. I have a stack of 600x 300 wall tiles, weight approx 20kg a box and there are 22 boxes in a stack 600x 600. Do the maths and that is 440kg/0.36m2 or 1220kg /m2

The floor has not gone anywhere. Could even work out the point loading of the multi gym in the same room that has 4 small feet and a lot of weights on it.

Trust me I'm a builder.

Edited By JasonB on 21/12/2017 12:37:31

Can't you just build a proper shed instead rather than put it in the house?

"Again I will say it. This is standard building practice slab or beam and block, layer of insulation, screed."

This depends on whether a "warm or "cold" construction (check the building regs), I chose " warm" construction after considering the possible loads in the workshop ares. looking at "cold" construction now, a more complex route to follow.

"Can't you just build a proper shed instead rather than put it in the house?"

I built my workshop as an extension to the house, insulated floor, insulated cavity walls and insulated ceiling (a foot of insulation!) so it could be heated with the house central heating, lovely to work in looking out at last weeks snow!

John

Just a thought, in Scandinavia polystyrene blocks are used for road foundations in areas where the ground is boggy, if you consider that the polystyrene in this case is totally encapsulated then whatever load that is exerted from above will be contained and spread throughout the structure. If roads in Scandinavia rest on polystyrene quite safely with no disasters then I don't think there is any cause for concern.

Dave W

John Mc one moment you say you are surprised that the polystyrene was where it is and ask if B. Regs were consulted and the next you suggest I look at the Building regs which show both and say you chose the opposite, If you had looked at the regs in making your choice they why were you surprised at the construction?

Does Martin need to ask two separate questions:

• as discussed already, will the floor take the overall weight, AND
• not really mentioned, will the floor take the pressure?

My feeling from what's been said is that a 1 ton machine in place should be OK. The pressure should be managed to keep the floor loading low, Martin Kyte's 150kg per square metre from BS6399-1, 1996 sounds reasonable. If that's right Martin D will need a big plate, but quite do-able.

What would worry me more is the possibility of damaging the floor whilst moving the machine into position. The pressure under the wheels of a crane or any rollers used will be high. I'm thinking of all those dance floors pock-marked by stiletto shod ladies.

Approaching the problem from the other end, what would be the maximum weight one would risk inside an ordinary house? (Assuming a concrete floor; no way would I put a ton on the wooden suspended floor in my mum's old house!)

Dave

Re: moving the item with a crane or rollers then definitely some form of spreaders would be necessary to prevent overloading with point contact. In 1965 we took a Spitfire into the Guildhall in London for a celebration of the 25th anniversary of the Battle of Britain, we brought the fuselage into the building on a modified bomb trolley and because the floor was ancient and priceless we had to spread the load with thick boards , basically really thick scaffolding type boards, we got a gold star , no flooring was damaged and they were most impressed with a nice shiny Spitfire as a centrepiece.

Dave W

As John said a 15 stone man standing in an area of 12" x 12" is equal to 1ton/m2 think we would all risk that.

I'd even be happy to let him stand of one leg which would be more than 2ton/m2 as the area could be halved.

Any one ever been on a building site and seen a 1ton bulk bag or a full pallet of plasterboard loaded out on a floor, I have.

One other point which hasn't been considered thus far is the degree of machine noise likely to be transmitted into the rest of the building and how that might be tolerated by others in the house and, if applicable, a neighbour sharing the structure.

Brian