Chiselling topped Column to add beams

[mes7a]

Are there *safe* ways to chisel the top of the column that is already topped with concrete to add a small beam? Or would the rebars (20mm grade 60) suffer fracture from the blows and not advisable in any way?

This is the column 2 years ago before the top were poured with 4000 psi ready mix concrete.

This is the column a month later after the top is poured with 4000 psi ready mix concrete.

 

[hokie66]

The reinforcement won't suffer significant damage, but the concrete will if the removal is too robust. The best way is to saw a line around the column to maybe 20 mm deep, then use a chipping hammer to remove the concrete.

 

[mes7a]

The reinforcement won't suffer significant damage, but the concrete will if the removal is too robust. The best way is to saw a line around the column to maybe 20 mm deep, then use a chipping hammer to remove the concrete.

Chipping hammer can vibrate the rebars and we are afraid it may cause weakening of the concrete rebar bonds below to the column-beam joint.. To be safe. We may just use manual hammer slowly. But the 4000 psi concrete has become like 5000 psi concrete (in actual test). Can you use manual hammer on a 5000 psi concrete? How long would it take?

Or have you heard about column face that is metal plated.. and the RC beam end metal plated too.. and they are joined by welding them together? This is to make sure the beam won't melt in a fire (which carries the firewall that is put above (what we were discussing in the other thread))

 

[mes7a]

Oh.. another thing to add.

Isn't it the column-beam joint has to be monolithic? can one with cold joints or breaking up in middle do? in other words, can I just chisel one half of it (vertically.. imagine only the right side of column is chiseled with left one remaining).. I'd just add a small beam enough to carry 1 meter parapet wall. Or does the entire top has to be chiseled and poured with new concrete? This is important to know. Because if this is so. I may waste so much concrete to create a small beam. So need to know this aspect of it. Thank you.

 

[hokie66]

I think you should be able to chip away part of the width of the column. I trust that the part above the cold joint was cast with column ties, and that your new beam/parapet wall will be adequately tied laterally to the column to develop the wall torsion into the column.

 

[mes7a]

I think you should be able to chip away part of the width of the column. I trust that the part above the cold joint was cast with column ties, and that your new beam/parapet wall will be adequately tied laterally to the column to develop the wall torsion into the column.

Have you got any references about using half width (or portion) of column as column-beam joint? And have you actually use such or know engineers who have tried them?

 

[hokie66]

References? No, but beams of different width than the supporting columns are common. I have used them many times. In fact, I never like to have beams the same width as the columns, as the reinforcement clashes.

 

[mes7a]

References? No, but beams of different width than the supporting columns are common. I have used them many times. In fact, I never like to have beams the same width as the columns, as the reinforcement clashes.

Even if you have beams of different width than the supporting columns.. they are casted monolithic.. the difference with the column mentioned in this thread is you suggest it would not be casted monolithic.. only half casted. This is the unusual situation. When the joint rotates.. only half of the width would be engaged.. half would be left.. this can produce torsion that can shear the concrete in between them.. won't it. I need to see studies of it.

 

[hokie66]

That is the reason for my comment above about the column ties. It is uncommon and poor practice to cast beams and columns monolithically.

 

[mes7a]

I know because settlement can produce gap in the column that can engage moment magnification effect if column-beam casted together at once.. but at least you cast the whole joint monolithically at once.. not half width at a time