Re: Snow load evaluation

["Robert Green" <ROBERT_GREEN1963@xxxxxxxxx>]

"Beamer Smith" <beamer@xxxxxxxxxxxxxx> wrote in message
news:qqspt2pmuqqthjqnvpv2374e3v10r8gdrg@xxxxxxxxxx
> Beamer Smith <beamer@xxxxxxxxxxxxxx> wrote:
>
> >
> >"Robert Green" <ROBERT_GREEN1963@xxxxxxxxx> wrote:
> >
> >>Anybody doing anything automated in terms of detecting an excessive snow
> >>load on a structure's roof?   I saw a news report about upstate NY where
a
> >>guy said "when your doors begin to stick, that's when it's time to clear
the
> >>snow off the roof.  It's good to know one of the warning signs but
surely
> >>there's got to be a better way!
> >
> >Less tech than the others but you hang a length of steel pipe inside a
> >slightly larger plastic pipe... (use wire so it doesn't stretch) a
> >quarter of an inch above a pair of contacts... when the roof sinks
> >that quarter of an inch the contacts are closed and what ever you
> >attached them to responds... low tech = light... high tech = sensor
> >that alerts a computer that dials a phone number that alerts the
> >media.. or whom ever.
> >n'est pas?
> >
> >Beamer Smith
> >Yes *that* Beamer Smith
>
> Oh and do it in the attic where the wifes visitors won't see it... ;)

That sounds like it might work but I'd be worried that time would eventually
cause enough of a sag to activate the detector without any snow load
present.

I've been fooling around with lasers and my video cam trying to see if I can
detect joist deflection.  I thought whatever worked for the basement and
first floor would also work for the attic and roof.   I was surprised to
discover that the laser beam diverged quite a bit more than I expected.  I
was also surprised at how little activity on the floor above was detectable.

I mounted the laser on the most unsupported joist I could find.  I trained
it on a piece of graph paper across the basement and then trained a videocam
on the paper.  My thought was that if there was deflection of the joist from
rolling a heavy power wheelchair over that spot, I should be able to see the
laser dot jump around on the video.  Nada.  About the only thing that made
the laser dot jump was jumping up and down on the floor above.  I need a
better way of amplifying the very slight movements involved.  I suppose it's
going to have to be the Pulsor sensors and some epoxy!

--
Bobby G.