Rebar for footings, up or down ?

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Re: Rebar for footings, up or down ?

Postby leoedgar » Fri Oct 26, 2012 8:24 am

splitlid wrote:heres a simple diagram of what is expected in concrete,the concrete in this case is your footing, by adding the steel in the bottom it holds the tension and prevents cracking etc.

your beams can act differently and the engineer has designed them specifically for your house so do as he designed.


The rebar for the footings and the colum is now going into the holes. I have bought some standard 6 cm concrete blocks, and cut eatch in 4 pieces. They have been leveled out in the bottom of the holes, so the rebar will be resting on this 5-6 cm above the soil. I will now fill up the hole with 30 cm of concrete, so the footing will be a 1 X 1 m concrete block, 30 cm heigh.
Next step is the colum, which will be casted up to a height of 70 cm above the ground level, which will be the bottom of the beams. The beams will be 20 X 30 cm, as I have told before, with a span of 3,6 m C-C to eatch colum. So here come my next problem, the "engineer" have suggested that for the rebar in the beams, I use 3 rebar in the top, and 2 in the bottom, but using the logic from your sketch, this beams will be bending down due to the load from the floor and wall, so there will be a lod of tension in the bottom of the beams. Is the something I don´t understand ? Asking the "engineer" the answer is, this is the way we always do it.
Any help will be apresiated.

Leo
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Re: Rebar for footings, up or down ?

Postby splitlid » Fri Oct 26, 2012 9:14 am

a pic of your beam plan and beam details would be good.
nothing wrong with it going by your description, beams can contain 4,5,6,8..................20.......pieces of steel, depending on span,loads etc.
your distance of 3600mm probably dosnt warrant extra steel in the bottom of the beam, the steel in the top is specified by the engineer so 'just do it'.

do you have 2 different types of beams? some with 4 some with 5?

could be that 2 in the bottom are sufficient for the loads above and the 3 in the top are for the undetermined forces from below incase of movement in the future.
:)
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Re: Rebar for footings, up or down ?

Postby leoedgar » Fri Oct 26, 2012 2:54 pm

Thank´s for your reply. I don´t have a drawing I can show right now, as the "engineer" is modifing it right now. He is acualy not an engineer, but designer, and asking him again why he did it like this, he said he just made a copy from another project, but I have bougt all the steel, so I will just continue with this, as I have also seen other drawings here on the forum, where they have the same combination of rebar.
All beams are the same. I have 20 colums in 4 x 5 rows, all rows are 3,6 M from C-C, exept 1 row where I only have 3,0, and all colums are connectet together with the said beams. When I get a new drawing, I will put it on here.

Leo
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Re: Rebar for footings, up or down ?

Postby leoedgar » Fri Nov 09, 2012 7:07 am

Here are some pic. of the drawings, any comments are very welcome.
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plan home-22jpg.jpg
plan home-20.jpg
plan home-2.jpg
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Re: Rebar for footings, up or down ?

Postby ajarnudon » Sat Mar 25, 2017 5:19 pm

" The beams will be 20 X 30 cm, as I have told before, with a span of 3,6 m C-C to eatch colum. So here come my next problem, the "engineer" have suggested that for the rebar in the beams, I use 3 rebar in the top, and 2 in the bottom, but using the logic from your sketch, this beams will be bending down due to the load from the floor and wall, so there will be a lod of tension in the bottom of the beams. Is the something I don´t understand ? "

This thread has been dormant for a long time, but thought I would post an answer to this question for the benefit of anyone looking later. The designer is correct, although he obviously doesn't know or hasn't got the language skills to explain why. The reason that there is more reo on the top of the beam is that over the point of column support, the top of the beam is in tension, not compression. The exception is at each end of the beam, where the beam is only in compression - some may choose to add additional steel at the bottom here.
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