swap tenon and mortise position?

[iwearhats]

I only do hobby related wood work, but I had a random thought about timber framing/wood joining in general after reading this.

https://woodworkersinstitute.com/features/2023/01/the-mechanics-of-joinery-2/

Why is it that say in timber framing the vertical post is the one that always adopts the tenon and the horizontal beam on top has the mortise? Is the reverse possible? Like the post having a U channel mortise cut out in the center(which I suppose is a double tenon) and the beam having the sides cut away to have a tenon in the middle for an open join.  Is this not done because of engineering concerns - because the direction of the forces (down on the beam) means that it's better to preserve more continuous material, hence mortise? Or is it simply an aesthetic issue because it makes it look like multiple small beams are spanning posts?

Like wise in furniture building(aside from aesthetics), provided we are working with thick enough wood pieces , is there any reason why say a table leg couldn't adopt the tenon, and the stretcher have the mortise? Say with 4x4 for both pieces. I understand that the table leg being thicker usually accommodates the mortise. 

Just a thought experiment.

[Don P]

Check out pic #10 here;
Timber Frame Education, Design & Joinery | Peter Henrikson

[rusticretreater]

When the horizontal beam is loaded and starts to sag a big, it will tend to pull a tenon out of an open mortise like you described even if it has diagonal bracing. 

[iwearhats]

So it appears it has been done before based on that link from @Don P. However, it's not common (or maybe less optimal) because of the reason that @rusticretreater pointed out? However, wouldn't the problem be mostly solved with pegs like it's done with the post having the tenon?