On Sun, 25 May 2008 19:11:03 -0700 (PDT), Fred the Red Shirt
wrote:

don't follow what you mean by 'shearing load is compressive'.
Shear, compression, and tension are three distinct orientations
of stress.

For a beam with a symmetrical cross-section, the sheer
due to bending is maximum midway between the upper
and lower surfaces. It is zero at the upper and lower surfaces.
From that midpoint up the stress is compressive, and maximum
at the upper surface. From the midpoint down the stress
is tensile and maximum at the lower surface.


If you look at the joint in the photos, is it more likely to
delaminate under load on the shelf with the tongue at the bottom, or
with the tongue at the top?



Regards,

Tom

Thos.J.Watson - Cabinetmaker
tjwatson1ATcomcastDOTnet
www.home.comcast.net/~tjwatson1