Avoneer
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| posted on 5/7/07 at 04:40 PM |
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Re-enforced Concrete Raft Foundation
Anyone any experience of these?
I've got an engineer to draw me one up as the calcs are important to satisfy the council.
He's mentioned forwarding me the bar-bending schedule.
Anyone know what's usually involved with the steel work?
Is it just solid rounds I can bend in my vice or something that's gonna cost me an arm and a leg?
Pat...
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Pdlewis
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| posted on 5/7/07 at 05:03 PM |
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U'll need the bending schedule you can then send this to a company such as lemon groundworks (not the cheapest but i know they are nationwide)
they will then either provide you with the seperate bent steel (at the correct grade) or if possable will fabricate the raft and ship it out to you.
I have done some simlar stuff but they were reinforced concrete retaining walls, they delivered in sections all we needed to do was wire together
shutter and pour very painless I wouldnt recomend bending the cars your self (some building controls can be funny about it)
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PeterW
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| posted on 5/7/07 at 06:05 PM |
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Whats his reasoning for a raft...??
Thickened Edge Raft foundations are only really necessary for unstable ground conditions that can't be satisfied by normal or reinforced ring
foundations.
Bending rebar is no fun - you can buy box sections though in pretty standard sizes.
More info would be useful if you have it
Cheers
Pete
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designer
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| posted on 5/7/07 at 06:17 PM |
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A reinforced raft for a garage. Over engineering at it's best.
Loads of rubble as the base and three inch of concrete will hold anything likely in a workshop.
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nathanharris1987
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| posted on 5/7/07 at 07:08 PM |
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I wouldnt touch re bars unless your actually working for civils or constr company.
Yeh some bends are just straight 90 degrees but the shape codes for the different bends are quite complex with stritct dimensions.
Ive got a copy of british standard 8110 if you want to have a look which states all of the standard shape codes, but you'd be best off by going
to your local reinforcement people who'd just drop the rebar off on a hi ab, completely prefabed so you get who ever to inspect it then pour
your concrete.
Also have a look at these guys BRC
I do agree with designer about loads of hardcore blining the foundation will hold anything but personally living in reclaimed land in south
lincolnshire, you get bands of running silt, peat fields and clay swelling and shrinking, literally everything is on a raft, including some
highways!
My company did a new pipeline last year, went for lunchbreak one day and the whole line had fell 300mm! Lively stuff.
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Avoneer
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| posted on 5/7/07 at 07:32 PM |
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It's for a two storey extension which goes over a drain 8ft down.
Piles were suggested, but there wasnt' enough room between the house foundations and the pipe for some of the legs.
Other than encasing the drain, a raft was the easiest solution and approved by the building regs.
All beginning to sound expensive for my self build!!! (apart from the bricking).
Pat...
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Peteff
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| posted on 5/7/07 at 07:52 PM |
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Chuck some old bike frames in it, always worked for me  The steel firm I worked at years ago used to make rebar in 416 and 431 and it was the
reeling shops worst nightmare trying to get it straight. It would need heat to get it to bend to a right angle and stay there.
yours, Pete
I went into the RSPCA office the other day. It was so small you could hardly swing a cat in there.
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JohnN
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| posted on 5/7/07 at 09:18 PM |
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If it is a simple raft, the bar bending schedule may be nothing more than steel mesh, in which case there may be no bending. The mesh will simple be
placed in the top and/or bottom of the concrete slab.
However, if the design is more sophisticated and involves integral beams etc, (I'd question the need) then you'll have individual bars to
get bent and fix in place and the bending will need to be done by suppliers. I'd go for a thicker, mesh reinforced slab. Talk it over with your
designer, he should be looking to provide you with a simple design, fit for purpose, not a rebar nightmare for a self builder.
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PeterW
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| posted on 5/7/07 at 10:34 PM |
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Just how big a drain are we talking here...?
At 8ft down, a 150mm drain requires a 125mm reinforced capping with a bearing of about 300mm either side - so about 750mm of mesh reinforced
concrete.
If its bigger than that, then it gets a bit more complex...
Just a daft question though... what does the drain do...? Is it a storm sewer or main drain, as it could be much cheaper just to re route it if it
only serves your property.
Otherwise, BRC will provide you with prefab beam sections that just need wiring together, and a few sheets of 192 and some chairs should see you
OK.
Cheers
Pete
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Ivan
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| posted on 6/7/07 at 07:32 AM |
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I agree with above - your designer should aim for stock re-bar mats.
Also if you have to use steel with bends, using a supplier that does the bending for you adds very little to the cost of the steel if you choose a
good supplier and is a pain to do yourself and comes labeled to match the schedule.
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Avoneer
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| posted on 6/7/07 at 09:37 PM |
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Drain is the sewer and every house on our side of the street goes into it and across the back of my house.
Thanks Ivan - that's made me feel a lot better - will ask the engineer when I get the plans of a good local supplier.
Pat...
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tony9876
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| posted on 8/7/07 at 01:54 PM |
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I am building a house at the moment that needs a concrete raft foundation with a retaining wall structure at the rear. I am struggling to find an
engineer to do the design.
I have the design for next doors build which was passed by the council but when i rang their engineer he wasnt interested in doing another as he said
it was too much hard work!!!
What engineer did you use and if you dont mind what is he charging you for the design?
Thanks
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Avoneer
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| posted on 9/7/07 at 12:21 AM |
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A firm in Morley, West Yorks.
£600 for raft including inspection and acceptance by the council.
Pat...
No trees were killed in the sending of this message.
However a large number of electrons were terribly inconvenienced.
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