Existing RSJs drilling and corrosion advice

[SuyinDB]

Hello,

First post here, though have lurked for some time! Hoping someone might be able to give me some advice about two existing RSJs that we've uncovered from above.

They both have a number of copper pipes crossing over them, but there's not enough room between the RSJs and the chipboard floor, so the pipes are squashed and noisy, and the floor is pressed up quite a bit. We would like to reroute the pipes through the beams. Am I right that if we follow these guidelines, then this won't be a problem structurally?

1. Drill holes in the centre (vertically) of the web
2. Drill holes within the middle third (horizontally) of the beam
3. Drill holes at a distance apart from each other of at least the height of the beam
4. Drill as small a hole as is manageable for the copper pipe to go through with some plastic insulation around it (to protect from corrosion in the future)

The other worrying issue is that one of the copper pipes must have gotten wet at some point, because it has corroded part of the top flange of one of the beams. The normal thickness of the flange is 9mm and it is as little as 5-6mm at the thinnest corroded part. Do you think we can just clean and paint this area, or will it need some kind of reinforcement? Would a general builder know how to do this, or would we need to involve a structural engineer?

I've attached photos.

Many thanks for your help!

Suyin

 

[jeds]

You don't say the span of the beam but assuming it's not more than about 4 meters and there are no point loads out of view then it is way over sized and will take a lot more load than that floor. You can comfortably drill 50mm holes in the centre of the web and the top flange is fine without structural repair. It would probably stay put if the flange wasn't there.

 

[Newboy]

The corrosion on the flange looks like galvanic action of the copper pipe in direct contact with the steel. You need to ensure that there is an insulating layer between the two metals in future.

 

[SuyinDB]

Hi John,

Thanks so much for your reply. I've attached a floorplan where I've marked on the approximate positions of the two beams. The span of each beam is ~4.6m. The flange width is over 13cm and the height of the whole beam is over 20cm. The party walls are breeze block, the partition walls are all paramount board, and above this is a flat roof. I'm afraid I'm not sure what a point load is.

And thank you Newboy also - yes, we'd definitely look to separate the two metals in future.

 

[SuyinDB]

An additional question... with the beam that has 7 pipes crossing it, we are not going to be able to space the holes 20cm apart and still stay within the middle third of the span (unfortunately we can't get access to the beam under the tiled bathroom floor, so we are limited to around 90cm of the middle third). Would it be OK to space them closer together, but stay within the middle third?

 

[jeds]

I've often done several (4, 5, 6) 30 to 50mm service holes 100mm apart at all points of beams and it makes absolutely no difference to the capacity of the beam - even when beams are very close to the serial limit. As long as the hole is close to the centre (vertically) the capacity is virtually unaltered. I've calculated long slot shaped holes 75x250mm for rectangular ducting in 203mm beams taking MUCH higher loads than you have there and the deflection results barely change. That beam is so large for the loads you can safely drill 30mm holes all along the beam and it will be 100% safe.

 

[SuyinDB]

Another quick question on this same topic.. What would people recommend for cleaning the corroded area of the steel flange after the copper pipe has been rerouted?