Vertical sleeves in R.C. Beams - Are there any special design considerations I need to be aware of?

[HermanLJ]

So the architect wants to run 110mm sewerage pipes vertically through some of my beams. The beams are simply supported 300x510mm and aren't subject to large shear forces (25kN max at the sleeves).

I know that for horizontal sleeves you have to add extra reinforcement for frame failure but I can't seem to think of anything for vertical sleeves. Google also turns up empty.

Can I just analyse it for a reduced cross section i.e. 300-110-10mm (just to be safe) = 180x510mm?

 

[BAretired]

This leaves only 90mm each side of the opening. I would be inclined to increase the beam width by 50 or 100mm for good measure. And make sure the opening is centered in the beam.

BA

 

[HermanLJ]

Yes that concerns me as well. Thankfully the beams aren't really structural beams, the are just there to house lighting and to reduce to effective length of the columns (so they will have a bit of axial force in them).

The shear capacity is sufficient if you treat it as 2 90x510mm beams but I still feel uncomfortable. Corbels might be the answer.

 

[BAretired]

Another thought is to use a round steel tube with welded anchors to the surrounding concrete to form the opening for the sewer pipe. The tube would be capable of resisting beam shear and axial force.

BA

 

[HermanLJ]

I did do that. My drawing had a galvanized circular hollow section sleeve with ribs welded at 20mm spacing along the outside so that it would act as a large piece of deformed rebar.

The contractor however thought that it wasn't necessary and cast the beams without them in order to save time. An absolute idiot. (I mean if it wasn't necessary I would have just specified a PVC sleeve). But that's life.

 

[BAretired]

I didn't realize it had already been poured. If it works by calculation, it should be okay but you may want to scold the contractor anyway. He had no business doing as he did.

BA

 

[HermanLJ]

Ag it's just another lesson to keep your eyes on whatever the contractor does. They always try to take shortcuts (no offence to any contractors reading this, I know the deadlines can be hectic).

Thanks for your advice.

 

[fel3]

Years ago, a seasoned engineer jokingly told me "We prepare plans and specs for our own amusement and the contractor does what he d*amned well pleases." Unfortunately, there is sometimes more truth than joke in that statement.

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"Is it the only lesson of history that mankind is unteachable?"
--Winston S. Churchill

 

[msquared48]

Really? I have NEVER found that to be the case!

Mike McCann
MMC Engineering