Concrete Column Demolition

[tally25]

I have a situation where a temporary concrete column supporting a post-tensioned concrete band beam above was installed early in the project. A new permanent concrete column was constructed about 1m away at a later date. The band beam was designed for both scenarios, but it is now time for the temp column to be demolished. Note I didn't design the columns or the band beam, so not aware of the history behind the necessity for this arrangement. Likely due to access issues early on in the project.

The demo contractor has proposed to use a hammer attachment on an excavator to remove the temp column. My concern with this method is damage to the suspended band beam to which it is attached. I also don't like the idea of the impact/vibration forces the works will transmit into the beam. Ideally I would like the column to somehow be cleanly and 'gently' detached from the band beam, and then it can be demolished with the excavator. This way there is minimal impact to the band beam, however I am not certain how this could be achieved.

Any ideas?

 

[Enable]

Hand chip the upper 6" - 12" of the column with 15lb pneumatics, and then use a metal cut off wheel on the quick cut to sever the bars. Do as you please after that.

I agree a hoe ram is likely to cause damage to whatever structure remains. That's why we restrict their use around vertical resisting elements to remain when replacing suspended slabs (usually 3' or so).

 

[Tomfh]

I agree you should score the top of the column first

 

[Retrograde]

I had a similar situation recently with an existing concrete column needing to be removed.

The contractor cut through the column using diamond wire sawing technology and removed the column in several pieces. It worked well.

The method is similar to this:

https://arrowconcretecutting.com.au/products-and-services/wire-sawing/

 

[Tomfh]

Good idea

 

[tally25]

Thanks for your comments all.

@Retrograde - yes I instructed them to use a wire cutting saw at the top of the column and demo the column below the cut line using the excavator. If they dont like that I will suggest cutting into several segments as you mentioned. Thanks for the link!

 

[lexpatrie]

Are you intending to accept liability for advising the contractor on their means and methods?

 

[tally25]

@Iexpatrie Of course not. Our job is to ensure that the contractors proposed demo procedure does not negatively impact the permanent structure. The execution and responsibility to ensure that the demo works be conducted safely ultimately lies with the contractor.

 

[lexpatrie]

I think in conventional liability you want to give them requirements to prevent damage to the permanent structure rather than endorsing (however informally) any specific approach and state that means and methods are the responsibility of the contractor but any demolition of temporary columns must be accomplished in such a fashion as to not damage the permanent structure AT ALL.

Dynamite and det cord, used "appropriately" could work, so could thermite, but these are unrealistic but you want to steer clear of specifics if you ask me.

They need to avoid excessive vibration, shore as needed, and remove the temporary column.

How they accomplish that is their means and methods and if they want advice on that, ask another engineer as you have a conflict of interest here. You work for the owner.