Coring through concrete beam

[asixth]

Hi guys,

I have a situation where an existing 600 x 190 beam (24" x 8") needs to be cored so services can pass through. My thoughts are that I should try to do this in a low shear region because the beam is not going to be scanned to determine the location of the shear ligs.

And I should core approximatley within the middle third of the depth, this way I will avoid any tensile steel and the compressive stress block should not be affected depending on the depth of the neutral axis.

What do others think of this logic.

 

[dik]

Best place is at NA of the beam near mid span where there is a low shear area and you are likely away from reinforcing. Use a Hilti meter or similar to check for rebar locations. Be careful and if possible run this by the EOR.

Dik

 

[csd72]

They should try and find the ligs using a stud finder or similar, this often works.

Otherwise, the use of a regular percussion drill for the outer 50mm would minimise the chances of coring through reo. Percussion drills dont tend to cut reo.

As per your question, yes I would think it reasonable to located the hole in the middle third, in the middle third of the beams span.

 

[msquared48]

If this beam is a transfer beam, be careful of the shears as the pattern will be different than for a uniformly loaded beam. In this case, if there is no EOR available, I would try to figure out the shear pattern, then test, mark and drill.

Mike McCann
MMC Engineering

 

[asixth]

What is the cheapest method to accuraltey determine the location of the reinforcement. They recently had an x-ray out there to scan the slab and it cost them $4,000AU ($3,000US). They do not want to go down this path again, and going by dik's response above I really should make some attempt to locate the shear lig.

 

[hokie66]

asixth,

You should be able to locate the stirrups with a cover meter.

 

[msquared48]

I have used a Zircon Videoscanner 5.0 for years on tilt-up walls. Won't tell you the size, but does locate well. Handheld. I've had it for 10 to 15 years now.

Mike McCann
MMC Engineering

 

[youngstructural]

I've had some success with stud meters in the past as well...

Hey Mike; Great tip! Love it when someone includes the precise product name. My Zircon is the little black jobby without a screen; Do you happen to know if the new Videoscanner (5.5 is the currently available model) works as well as your 5.0? Just worried they might have reduced the strength, or improved the software for timber which might have limited the general application. Thought I'd ask on the off chance you know...

Cheers,

YS

B.Eng (Carleton)
Working in New Zealand, thinking of my snow covered home...

 

[msquared48]

Sorry, but I don't. Of all places though, I bought it at Ace Hardware.

Mike McCann
MMC Engineering

 

[asixth]

YS / Mike,

Were the videoscanners bought by your company or did you purchase one for your own personal use?

 

[hokie66]

asixth,

A cover meter should be standard equipment in a structural engineering office.

 

[hokie66]

This is a good piece of equipment, and not as expensive as some others.

http://www.wallscanner.de/en/start/index.htm

 

[asixth]

Hokie,

Thanks mate, I put it to my company today to purchase a cover meter but they didn't like the idea. So I think I might have to buy a cover meter myself. I might go down the hardware store and see if they sell any down there.

BTW, I have attached a picture of the beam that they want to core through, I have done some numbers on the beam and it looks like it is in a low-shear zone however, I want to try and avoid the shear ligs if possible.

 

[csd72]

asixth,

I wouldnt go out and buy one yourself as they are not cheap, and it is really up to the contractor to do. These can be hired if necessary.

The 'beam' that you show on the picture looks like a ventilation duct to me. There is no chamfer in the corner and on the right hand side appears to be a few creases in the metal. Also it looks nothing like the beam beyond it.

 

[hokie66]

Does look like ductwork. From the picture, it is hard to pick out the concrete beam. I am sure apsix knows a beam when he sees one, but coring the ductwork should be dead easy.

 

[apsix]

I do, and I'm sure asixth also does

 

[OzEng80]

Asixth - if it is in a low shear zone, it might be easier just to determine if the ligs are even needed (V*<0.5 phiVuc). If not, you don't have to worry about locating the ligs.

 

[hokie66]

apsix,

Sorry, must have been a senior moment. I get you x-guys confused.

 

[asixth]

There is an existing duct going through the beam I want to core through, this penetration was considered during the original design in 1975.

The beam the duct passes through is 600 x 290, the transverse beams that frame through this beam are 450 x 190 at 1450 c/c, and they span to beams that are 900 x 290 and are at 8500 c/c.

Slab over is 100 deep.

This wasn't the best picture to psot so I will post another.

 

[csd72]

So its the one with the metal trim along the bottom that you are framing into.

Steer clear of the edge of the duct penetration as this will have extra shear reinf either end. Also there will be an extra row of horizontal bears at the top and bot of that penetration that you need to miss.