Flitch beams and service notches/holes

[champagnecharly]

I'm looking at a loft convertion where headheight is more than a luxury to work with. I am therefor looking to use shorter/thinner timber by using flitch beams.
but then came a thought. what about service notches/holes and their effect on the beam? It seems strange wrong to reduce a joists height to 122 and then put a 32mm or 38mm hole in it as that would be a substantial point of weakness. I can see guides on general notches in joists but nothing with regards to fltch beams. Are there standard rules for the same? I.e. MAX hole size:BeamRatio?

 

[theprinceofdarkness]

Do a search, this has been covered before here. FWIW cutting the hole through the centre of the beam causes it less stress.
Frank

 

[champagnecharly]

Thanks... I always search through similar posts prior and post myself as a last resort.
Maybe you know the thread or the keywords I should search under. If so I'd appreciate if you could point me in the right direction

Searching on "Flitch Hole" Or "Flitch notch" "flitch Service" returns zilch. Obviously searching "flitch beam" I get 1000s of seemingly irrelevant posts.

Drilling in the center (top to bottom) I took as being read the same way as not drilling in the middle of the beam. But its the ratio of hole to not that makes me wonder.

 

[tony1851]

It seems strange wrong to reduce a joists height to 122 and then put a 32mm or 38mm hole in it as that would be a substantial point of weakness.

Not necessarily.

In a flitched beam, practically all the stress is taken on the steel plate - the timbers each side add only a marginal amount of strength and are mainly intended to stop sideways buckling of the plate.

The steel is very strong in relation to the timber and is far more tolerant of holes being drilled in it, though you would need to get an SE to do the figures to check.

 

[champagnecharly]

Thanks.

Maybe I was overly worried. As you say strength of steel is what takes the load.. so on that bases of that If the guidelines for notching joists are used Max d/3 min 2" from edge etc then I can deduct what the max allowable holes are. And just because as "standard" the steel plate is D-25 doesn't mean it has to be. If things are tight in terms of hole size or distance from edge where D/3 or min 2" then either depth of joist and or depth of flitch plate can be increased. I.e. common sense to be applied.

Also on the basis of what you said re sandwich, and the D-25, it may be simpler to calculate the flitch plate & timber on a bases of FlitchPlateDepth = D-MaxNotchDepth.

Well I think i got it now.. If something i said didn't sound right please please please correct me.

Thanks again