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I have a number of 12" square concrete piers reinforced with 10 * 16mm rebars. The rebar extends to around 4m tall, while the concrete has been poured to a height of 3.3 metres.

This an error because the intended height of the bottom of the upper floor is 3.3 metres; however, as a 40cm concrete beam is planned to support the upper floor, this means that the height of the poured concrete should only be 2.9m, to allow for a 40cm beam on top.

So I am considering chiselling 40cm of concrete off the top of the pier and placing the rebar there. Does that pose structural concerns for the strength of the pier?

  • I would use a cement cutting disk, the disk will cut the rebar. If you chisel it may fracture the cement. On a job this large I would rent a large gas powered cutoff saw. But a 9" angle grinder may be a bit cheaper and then you will have a nice grinder to use whenever you need it. Remember to use a dust mask and safety glasses. – Ed Beal May 21 '16 at 9:56
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    This seems a bit too heavy-duty for our DIY scope. – Daniel Griscom May 21 '16 at 11:03
  • Is this commercial or residential? – Aloysius Defenestrate May 21 '16 at 14:29
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You almost certainly do NOT want to cut off the rebar in the columns as suggested by @EdBeal - that should be tied in and/or bent and tied in to the rebar in the beam.

I'd think long and hard about just raising the upper floor by another 40 cm rather than chiseling all those columns - but if they are freshly poured, you may find that they will chisel easily, as the green concrete is still going to be relatively weak.

  • I was considering raising the floor and maybe reducing the height of the upper floor to compensate. The issue is there is a rock behind the building around two storeys high, so I don't want to end up with a building that's too high. – thelawnet May 21 '16 at 14:46

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