[VAC] Re: Structural loading / aircraft flooring

["Dr. Gerald N. Johnson, electrical engineer" <geraldj@xxxxxxxx>]

The C channel has two flanges and the web that separates them. Its a
poor cousin (structurally and cost wise) of an I beam. An I beam has
three parts, that are two flanges and the web that separates the
flanges. The shear connection from flange to web is critical and in
rolled channel and I beam has extra metal. I envisioned house floor
joists with two 2x6 flat for each flange, and one 2x6 as the separating
web. So long as I ignored the shear at the connections it was a super
strong beam. When I asked a structural engineer about it, he pointed out
the flaw was in that flange to web connection. It could be made, but
would require 16d spikes into the edge of the web ever 3/4". I believe
most ordinary 2x6 would split on the dotted line into a pair of useless
1x6. Or else making a perfectly fitting glue joint and using a $25 a
quart structural adhesive.... I've changed my house design, but I still
have all those 2x6 on hand...

It doesn't take a strong filler to hold the webs apart. Foam or
honeycomb in aircraft floors and wings does well. Might not do so well
if the flanges were 1/4" steel that would push a lot harder than .032
aluminum.

Helium is hard to hold in without very good welded seams and then it
leaks easily. Its often used to test welded seams in electronic
components. Even if helium weighed nothing, it would only reduce the
vehicle weight by the volume of air displaced, which in the Airstream
walls, isn't much.

The simplest concept in doubling frame strength would be to double the
frame member thickness, increase the frame member height (both requiring
wholesale replacement of the frame and lower skin), or most simple to
add another channel the same size as the original to make a box or I
beam. Scabbing another piece of the same sized channel to make a box or
I beam is the most simple technique.

When a bedroom floor moves when I walk across it, it might not like the
total weight of the early water bed. I hear they make them lighter these
days to solve many of those structural problems. It makes a big
difference in the floor load whether the water is 18" or 4" deep. And it
makes a big difference to the house floor structure whether the bed sits
on four points or is a distributed load. A floor made to minimum HUD
specifications can be kind of wimpy.

The frame would benefit the most from added material near the middle at
the axle(s). There's where the bending moment from distributed or point
loads is the greatest. Its like a see-saw. I've never seen one break
anywhere but at the pivot. That's because that's where the stresses are
the greatest. A trailer frame is a see-saw. Doubling up the frame
material out at the back or up close to the hitch isn't quite as an
effective use of added material.

Trouble with the body of potable water is that we make it less potable
by crapping in the woods. Might not need the aluminum box, just a cover
to keep the rain off and a sleeping bag, carry it all on our backs, sit
on logs (if in a country side that has trees to cut into logs). Been
there, tried that (at Uncle's orders, and a little on my own), I think I
rather like parking the A/S and being ready for bed or supper in minutes
instead of hours. Besides its hard to set up posts on a blacktop Walmart
parking lot that might hold up the rain cover. And I don't grow fur on
top my head well anymore.

Gerald J.