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>:
>>
>> >"Robert L Bass" <sales@xxxxxxxxxxxxxxxxxxxxx> wrote in message
>> >
>> ><stuff snipped>
>> >
>> >>Use nailing plates to protect the wires.  However, these do not restore
>> >>any of the strength of the framing member lost by drilling or notching.
>> >
>> >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?

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. If you have big knots or other weak spots,
there can be shear failure.) So boards that extend a two hole diameters to
either side of the hole should be ample using three screws per side
(assuming steel or plywood that won't split.)  But as others have written,
if the hole is in the center of the beam, little strength (~= resistance to
bending) is lost.

... Marc
_F_Hult
www.ECOntrol.org