Re: Hole Diameter for running cable

[Marc_F_Hult <MFHult@xxxxxxxxxxxxxxxxxxxxx>]

On Wed, 29 Nov 2006 23:27:50 -0500, "Robert Green"
<ROBERT_GREEN1963@xxxxxxxxx> wrote in message
<VcWdnUZsCdNow_PYnZ2dnUVZ_uGdnZ2d@xxxxxxx>:

>"Marc_F_Hult" <MFHult@xxxxxxxxxxxxxxxxxxxxx> wrote in message
>news:63jrm2tslvp5p5gn4q7nuksoigi8b1cb4o@xxxxxxxxxx
>> On Wed, 29 Nov 2006 06:11:08 -0500, "Robert Green"
>> <ROBERT_GREEN1963@xxxxxxxxx> wrote in message
>> <apGdnVhjMPZi9vDYnZ2dnUVZ_vqdnZ2d@xxxxxxx>:

>> >What does?  How would you run wires in a way that didn't reduce the
>> >structural integrity of the framing?
>>
>> One can use a prefabricated metal gusset scabbed to the joists
>> and(or)attach  custom metal or plywood reinforcements to the sides of the
>> framing member. This can restore all lost strength and then some.
>
>My predisposition is to clad the affected joist with 3/4" plywood scraps
>attached by countersunk woodscrews.  I have a lot of nearly 1' by 4' by
>3/4" scraps from a previous project.  What length of brace would you use,
>assuming you're covering the entire height of the joist?
>
>While I probably won't do any bracing for 1" holes or less, the 2" vacuum
>cleaner pipes bother me.  I just measured the joists and they are only 8"
>so a 2" hole removes a fair proportion of the material.  I hear the floor
>groan when Dad visits in his power chair so I am concerned that I might
>already be overloading the structure with all the books and file cabinets
>we have.

It helps to remember that the purpose is to reduce the flexing of the beam
(assuming the holes are not at the very ends of the joist).

The material at the top of the beam resists flexing because it resists
compression. The material at the bottom resists extension (stretching).

There is a plane in the middle that is neither stretched nor compressed --
that is the material that does not add to strength and is just added weight.

If you remove that material, you don't increase flexing of the beam.  (This
assumes a homogeneous material -- no big knots or other weak spots.) So
scabbed boards that extend two hole diameters to either side of the hole
should be ample using three screws per side (assuming steel or plywood that
the screws  won't cause to split.)

But as others have written, and as explained above, if the hole is in the
center of the beam, little strength (~= resistance to bending) is lost.

... Marc
Marc_F_Hult
www.ECOntrol.org