On Wed, 12 Feb 2020 12:18:51 -0600, dpb wrote:

On 2/11/2020 8:24 PM, dpb wrote:
On 2/11/2020 8:00 PM, DerbyDad03 wrote:
On Tuesday, February 11, 2020 at 6:46:01 PM UTC-5, dpb wrote:
...

...[snip for brevity]...

Sagulator gave 0.11" for "Plywood, fir" and while Doug fir wasn't one of
the firs it gives specifically, they all were less (altho not by factor
of 2 which does seem somewhat excessive by common experience).* It
doesn't have any other plywood to compare against.

And just about any kind of edging on just about any kind of wood makes
all those specs moot. ;-)

No, it does not.

All it does is change the geometry somewhat but the effect is also
easily calculated.* sagulator has the option to add the edging.

What you can't see in it, unfortunately, is just what data it is using
for the materials properties.* I don't recall whether it has the ability
to input the desired properties manually or not.

Just to confirm what sagulator does; went to the "Engineering Toolbox"
beam calculator for rectangular, uniformly loaded, pinned joint beams
and entered the necessary info for a 3/4" x 36" shelf with no edge
material included in the calculation of the moment of inertia and an
assumed modulus of elasticity of 1.2E6 to guess what it uses for
"Plywood, fir".

And indeed, voila! it returned maximum beam deflection of 0.108" while
sagulator only reports two digits of 0.11". It's a simple beam
deflection calculation.

Also confirms the plywood E appears to match that from the FPL handbook
(which is what I thought I recalled from doing the exercise in the past).

If one doubles E in the beam deflection calculation, the maximum
deflection is then 0.054", precisely half as the maximum deflection for
the assumed geometry and loading is proportional to L^4 but inversely
proportional to both E and I.

Let's see if sagulator is more sophisticated in the edging calculation
than just adding the extra I, not counting for the induced asymmetry...

Adding a 3/4 x 1 edge also of the same material, the beam calculator
returns max deflection of 0.0941" where as sagulator is again limited in
its output precision so returns only 0.09".

Again they match so that's all it's doing -- the total moment of inertia
is simply the sum of the two composite pieces.

https://www.engineeringtoolbox.com/beam-stress-deflection-d_1312.html

The only additional sophistication in the sagulator is that it can
select a different material for the edge so the overall effective
modulus of elasticity is a little different whereas the beam calculator
is primarily intended for structural beams, etc. so is single material.

Who would have expected differently? It even says it in the text, or
it did at one point. This doesn't change its utility.