bilbo*baggins wrote:
Every basic primer on 'beam theorty' explains that the majority of Load
on any beam is carried through the 'top' and the 'bottom' surfaces.
There is a close relationship between the amount and nature of the
material in the 'top' and the 'bottom layer', and the distance apart.
Consider the shape of a steel I-beam.....
Consider the same shape of an 'engineered wooden beam'.......
Consider the shape of your floor joists, and recognise that there's
quite a lot of wood doing nothing.

Essentially, the wood along the mid-line ( the neutral axis ) is only
holding the rest - the stuff doing the work - sufficiently apart.
That's where any cutouts and holes for services should go.

Any notcheds and cutouts in the upper or lower surfaces are seriously
weakening the joist-beam, and should be repaired. Think of it this way
- would you happily fly your family in an aircraft where cutouts had
been made to the wings' mainspar, by someone unknown?
No, I didn't think so.


Actually beams in floors are totally overdesigned, so as to achieve
STIFFNESS. Not ultimate strength. The STIFFNESS is not actually reduced
that much by the odd knot hole or notch.

Sure the floor is weakened, Maybe it will only take 30 tons instead of
50...but the plaster underneath will be long gone before it gives way...