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  1. #1
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    Rebars and concrete

    Does anybody bought rebars recently ? I would be interesting about prices of 6 mm and 16 mm. I just got some plan for my house and there seem to be lot of 16 mm steel just thinking that is it normal to use 16 mm rebar in columns and beams. My first thought was that it is over calculated and 12 mm would be enought for one floor house. Is it possible to replace 16 mm rebar with 12 mm rebar if use more that smaller one ? For example replace 4 pcs 16 mm rebar with 6 pcs 12 mm rebar. 12mm rebar would be much more easier to bend.

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    Quote Originally Posted by raid71
    12mm rebar would be much more easier to bend.
    indeed , suggest you now go and read the story of the big bad wolf and the three little pigs

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    raid71

    What you have suggested is in one way correct BUT and it is a very big but there are other requirements that must be taken into consideration as well.

    The tensile strength of the steel is directly related to its cross sectional area so in theory 16mm could be replaced by an amount of 12mm which gave the same cross sectional area of steel. Now comes the BUT, as important as the amount of steel in the beam is where it is placed. so 1 peice of 16mm versus 2 x 12mm and now the steel is not located correctly within the beam to give the correct tensile strength required. It is also important that the steel has the correct amount of concrete cover (which would be specified on the structural plans).

    I work in the mining industry and we design our excavations to meet a factor of safety of about 1.1 so that it only stays open just long enough to extract the ore. If we desined with a factor of safety of 2 then we would be spending too much money. The factor of safety for most civil engineering projects would be greater than 10 as the consequences of a failure are unacceptable. So if you are prepared to worry for the rest of your time in the house, that it may fall down at any time, then you can save some money. I would rather spend a little bit more and sleep at night knowing that even a magnitude 7 earthquake won't send the roof down on my head.

    As Mid said read the "Three Litlle Pigs".

    My advice, don't do it.

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    raid71, did you calculate how much you would save?

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    If your plans say 16 and you use 12mm your project will be stopped.

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    Quote Originally Posted by raid71
    I just got some plan for my house and there seem to be lot of 16 mm steel just thinking that is it normal to use 16 mm rebar in columns and beams.
    why don't you talk to the engineer that did your plans, I am sure he would be happy to explain

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    Quote Originally Posted by raid71 View Post
    Does anybody bought rebars recently ? I would be interesting about prices of 6 mm and 16 mm. I just got some plan for my house and there seem to be lot of 16 mm steel just thinking that is it normal to use 16 mm rebar in columns and beams. My first thought was that it is over calculated and 12 mm would be enought for one floor house. Is it possible to replace 16 mm rebar with 12 mm rebar if use more that smaller one ? For example replace 4 pcs 16 mm rebar with 6 pcs 12 mm rebar. 12mm rebar would be much more easier to bend.
    Columns are one thing beams are quite another. Whilst columns can often be subjected to a bending moment, beams generally always are. You can't just go replacing 12 for 16 (though it will almost certainly be OK) without recalculating - I expect your engineer won't like it.

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    Hmm-much sage advice here.
    I am an old formworker and there is one thing that I remember.
    No,two actually.
    The first one is that when building stairs this is important- twice the rise plus the going should be 23 or 24 inches.
    The other is that concrete is strong in compression but weak in tension.
    Most here will understand-columns are always stronger than beams.
    I know that reo is quite expensive now,but your savings are bugger all.,
    Did you see that quake in NZ the other week,Id go for big diameter reo myself.
    I live in a phnom penh shophouse that cost $26,400.
    Nineteen metres by four with 2 beds ,two baths and a flat concrete roof only fifteen minutes from the city.
    BUT!!!!
    Columns and beams are weak,most reo is a wire about 4mm in diameter that comes in a roll and has to be straightened.
    Right above my bed on the mezzanine is a beam about 250mm by 350mm.
    It will kill me if we have an earthquake-think about it.

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