Calulating Rebar needed

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Re: Calulating Rebar needed

Postby Cheeryble » Sun Jun 07, 2015 11:01 am

This is an old but very informative thread, many thanks to Jazzman.

Rather than go into all the detail, is there a simple formula I can use to add the rebar cost to the concrete cost for the structural members and floor (which will probably be laid straight on compacted dirt).

ie
I know concrete comes in at 1500-2000bt/m3.
Mine will be made on site with a mixer so perhaps the lower end?
I have seen someone suggest doubling the 2000 figure allows for the rebar.

Is this reasonable or overkill.......bearing in mind my guesstimating is for a single story lightweight block structure (2 actually) with a lightweight metal sheet roof or "asbestos" roof. Basically two single room chalets with a non load bearing concrete floor.

In a word:
How much / m3 for concrete and rebar averaged through the whole structure for very light weight load bearing?

Thanks!
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Re: Calulating Rebar needed

Postby Roger Ramjet » Sun Jun 07, 2015 1:53 pm

Cheeryble wrote:Rather than go into all the detail, is there a simple formula I can use to add the rebar cost to the concrete cost for the structural members and floor (which will probably be laid straight on compacted dirt).

If you are real about saving, why use rebar in the floor at all, just use trench mesh.
There is no formula, each house is different, each column and beam is different, you can even save more money by using straight 9mm rebar instead of deformed. And there are three grades of rebar, go the cheapest that'll probably save you another10 baht a metre.
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Re: Calulating Rebar needed

Postby Cheeryble » Sun Jun 07, 2015 3:50 pm

Thanks for the thoughts Roger
BTW what size are the panels of steel mesh you speak of they may be fine for the floors?

Would anyone hazard a guess at the overall cost of concrete/rebar/mesh per cubic metre averaged through the whole (lightweight) building?
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Re: Calulating Rebar needed

Postby canopy » Mon Jun 08, 2015 8:02 am

To answer the original question, specifications for slabs often talk in terms of kilograms of steel per square meter of concrete. So you have to make sure your mesh roll is heavy enough; not just any old roll will do. Or you can make your own grid from regular rebar. The bigger the bar, the wider the spacing to achieve the necessary weight. So perhaps a suitable mesh roll may be 8cm squares, but running 12mm rebar may only need to be perhaps 40cm squares. I like the bar grid method. It stays real solid during construction and you can select the same size bar used elsewhere to minimize leftovers.

Speaking of specifications, what I really like for slabs is the Australian design that makes a slab an impenetrable termite barrier. It requires more steel, vibrating, and other techniques not normally done here. But when you are done, no termite will ever go through your slab. So not only is the slab extremely strong and built to a high standard, but you don't need to waste money spraying harmful poisons on a regular basis.
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