Core Drill & Rebar

[Alwayslearningelec]

Anytime you core drill through a slab I imagine you can hit rebar. Is x-raying of a slab always required and if not how to you avoid the rebar? THanks.

 

[cadpoint]

Static poured floors for conversation is not a problem the holes are to small, Dynamic Floors that are loaded with pulled tension strains is a whole different story. X-ray any tension floor.

 

[Alwayslearningelec]

Static poured floors for conversation is not a problem the holes are to small, Dynamic Floors that are loaded with pulled tension strains is a whole different story. X-ray any tension floor.

Ok and I guess the structural spec has t be reviewed in order to tell what kind of slab has been poured, post/pre tention etc.???? Thanks.

 

[charlietuna]

None prestressed slabs with re-bar are no match for a coring machine -- just goes a little slower as you go thru the rebar. Of course it can go thru a raceway too???

 

[handy10]

The issue is not whether the bit will cut through the prestressing member, but whether the floor will loose too much strength if the member is cut. Many prestressed floors a prefab slabs with cable tunnels. These tunnels could be located with a small drill without cutting the cable.

 

[hurk27]

Just use a good metal detector/locator's, in the past I have even used those ones that retired people comb the beach with

Cutting into a pretensioned cable is not a good thing and can be a very costly mistake!

 

[LarryFine]

Cutting into a pretensioned cable is not a good thing and can be a very costly mistake!

It makes a big noise that can be heard throughout the building, too. Trust me. :roll:

 

[Rockyd]

X-ray is way smart in questionable territory. Better to lose the job to "Joe-cheapo" than be explaining to your insurance agent "Then there was this loud sound, and ,and ,and..."

Risk analysis depends on a lot of factors. Choose wisely!

 

[Wingrider]

Rebar detection

Rebar detection

I worked over 20 years at Diablo Canyon NPP, where is was forbidden to cut rebar during core drilling. We used a ground detector device that plugged into a grounded receptacle, then the core drill plugged into this device. When any metal was encountered during the drilling process the unit tripped. I have been unable to locate one of these devices, as the question just came up at my new job on how to avoid cutting the rebar. This inexpensive device alleviated the need for X-ray, GPR, or magnetic imaging. Where do I find one of these devices? What is it called?

Thanks.

 

[Fulthrotl]

Anytime you core drill through a slab I imagine you can hit rebar. Is x-raying of a slab always required and if not how to you avoid the rebar? THanks.

milwualkee makes a metal detector for about $400 that works well..... i've
verified results right alongside a guy doing ultrasound, and i'd trust it,
but not on a POST TENSION deck.

cables on post tension are 1/2" cable, sheathed in greased sleeves, pulled to
20,000 lbs tension, most of the time.

i broke one, once, in 1984, on the meridian hotel across from john wayne
airport. i was trying to locate a buried red dot in the slab, and was directed
by my foreman to do so with a hilti TE 72 with a bull point on it.

i just barely nicked it, and the sound was like a 30-06 going off in a tile
bathroom. the cable came out the side of the building, went across the
parking lot, as it was 4 floors up, and went thru the glass on the office
building next door. it also blows out chuncks of concrete 6" wide and
4' long, where the peaks and valleys in the cable are at in the slab.

nobody was hurt.

repair of the cable back then was $15,000.
now, it runs about $80,000 i was told recently.

post tension, i x-ray before hand with a licensed guy... then i use
my metal detector over the area to detect any metal before i cut,
and i get my lucky rabbits foot out of the work truck as well, in
case i need it.


randy

 

[cowboyjwc]

Post tension slabs are sometimes stamped with a warning, but I wouldn't count on finding that on a commercial project.

 

[K8MHZ]

None prestressed slabs with re-bar are no match for a coring machine -- just goes a little slower as you go thru the rebar. Of course it can go thru a raceway too???

In my first year as an apprentice I was asked to help find an open circuit in a factory. I had worked in industrial maintenance before I came into the apprenticeship and loved chasing down wires. I located it, someone had core bored a 4 inch hole through a 2 inch rigid pipe in the poured concrete floor. They cut right through all three phases of a 60 amp 440 volt branch circuit. I always wondered how that could have happened without the person doing the boring noticing. First, the circuit was live when it was cut. Second, have you ever done a bore through a wall or floor and not looked into the hole when you were done????

 

[Alwayslearningelec]

In my first year as an apprentice I was asked to help find an open circuit in a factory. I had worked in industrial maintenance before I came into the apprenticeship and loved chasing down wires. I located it, someone had core bored a 4 inch hole through a 2 inch rigid pipe in the poured concrete floor. They cut right through all three phases of a 60 amp 440 volt branch circuit. I always wondered how that could have happened without the person doing the boring noticing. First, the circuit was live when it was cut. Second, have you ever done a bore through a wall or floor and not looked into the hole when you were done????

HA!!! That's funny...but not really

 

[zbang]

Second, have you ever done a bore through a wall or floor and not looked into the hole when you were done????

I'm pretty sure that the drill operator did notice, but packed up and left before anyone else did.