Justification for cutting through rebar

[George1985]

I have to write up a calculation which justifies cutting through rebar in a underground concrete wall which is a part of a pullbox which houses underground cables. Basically we're making a 4" diameter core drill and cannot avoid cutting through horizontal and vertical rebar. The rebar is 1" diamter and has a 7" vertical spacing and 6" horizontal spacing. The wall is 14.5 feet tall, 10 feet wide and is 12 inches thick. Any tips on how to calculate this would be helpful.

Thanks in advance.

 

[msquared48]

Why can't you core a 4" diameter hole through a space with a 5" clearance? Is the location of the hole that critical it cannot be shifted 3"?

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[George1985]

yes basically. i am anticipating that they will have to cut through rebar.

 

[msquared48]

I would have them locate the rebar and DEMAND it not be cut. The 1" diameter bar to cut at the spacing noted means a highly loaded wall to me, and would find a way not to do it.

Otherwise, you may be looking at replacing the structural contribution of the cut steel, somehow.

As a side note, if uyou must cut the steel and the wall spans vertically, cut the horizontal steel. If it spans horizontally, cut the vertical steel. The impast structurally will be far less.

Hopefully the wall does not span both directions, but effectively can.

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[George1985]

I agree the wall is loaded. It's an underground pullbox, basically it's a concrete rectangle of rebar/concrete, all underground except the top is open. My question is, what is a calculation I can use to check the impact of cutting the rebar?

 

[msquared48]

If you are not familiar with concrete design, I would suggest involving a structural engineer here, as what is the primary wall reinforcing may not be evident to you.

In fact, if this associated with a nuclear plant, strength to resist soil pressure may not be the conrolling issue here. It may be explosive in nature.

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[UnneutralAxis]

If you are a nuclear engineer, you are obviously a smart person. But I would no more want to try out nuclear engineering than I would want a nuclear engineer to try out structural engineering.

I would venture to say that reinforced concrete design is one of the more complicated aspects of structural engineering. It would be best to involve a structural engineer here.

Good luck!

 

[George1985]

I agree with you guys, I'm actually mechanical havent changed my info. I do work at a nuclear plant and most definitley will involve a structural engineer here, but was just trying to get this calculation going on my own today, I like to get ahead of the game sometimes. Thanks for the replies and information.

 

[a2mfk]

Cheaper and easier to listen to Mike than to repair the cut rebar or prove you should cut it in the first place. Hire a detection company to come out and locate the rebar, verify by drilling small pilot holes if you have to, and then coring between the rebar..

 

[msquared48]

Good suggestion a2...

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[Den32]

Agree with A2 and MSquared - the contractor should be able to locate the bar using special equipment (most local concrete testing agencies probably have this equipment).

If they absolutely must hit the bar(s), then you would need to calculate the wall forces (per code) and determine the capacity minus the bars that were cut (per ACI 318).

It is beyond this forum to get much further into it, best bet is to get with a Structural Engineer for these calculations.

 

[George1985]

I appreciate all of your input. A structural engineer is on it!

 

[ukengineer58]

just a comment, generally would you all think a 4" hole would likely be a problem. I don't see it. Accept that a nuclear containment vessel is a bit different and we don't have all the details but this kind of hole will have very little impact I would think, depending perhaps on location.

 

[Zambo]

how did we find out leist22 is working at a nuclear facility? But he mentions that the top of the structure is open which suggests it isn't a critical nuclear structure such as a containment vessel.

leist22 calls this a pullbox, I think this is what I would call a drawpit, basically a manhole for cable installation.

I tend to agree with ukengineer58 that this might not be critical. I guess the wall has rebar on the inside and outside face, perhaps only the rebar on one face will be cut.

 

[George1985]

Correct this is a cable pullbox NOT a nuclear pressure vessel or containment or anything which houses anything nuclear/radiation related. Structural engineer did a calc and determined it was acceptable to core drill a 4" hole through some rebar. Work was delayed so a calc was needed in a hurry and I made an attempt to tackle it, being a mechanical engineer I wasn't sure how to approach it, so I asked you guys, and realized I needed the support from a structural engineer.