On Apr 18, 12:38*pm, wrote:
On Sat, 18 Apr 2009 11:44:05 -0400, "Eisboch"
wrote:







wrote in message
.. .
On Sat, 18 Apr 2009 08:02:46 -0400, "Eisboch"
wrote:

We also had a pool enclosure installed at that house. *By that time the
code
requirements were for 150 mph winds.
It was installed by a reputable and licensed company but "Wilma" still
pretty much destroyed it with 120 mph gusts.

I was involved in some post mortem inspections of failed screen cages
after Charley. It appears the first thing to fail is the cable stay
system, then the screen cage just shakes itself apart. I really
believe these should be designed more like a bi-plane than a bridge
with more cable stays. The forces are more similar.
One of the mitigation in the subsequent code was more diagonal bracing
in the roof to give them better dimensional stability.

I don't know if this is true or not, but it was suggested to me that in
hurricanes, it is best to remove or open any doors on the pool enclosures.
The screen sections are installed in a manner that is supposed to allow them
to "blow out", reducing the surface that the wind can capture and thus
reduces the loads on the aluminum frame and braces. *Leaving the doors open
allows the wind "pressure" *to equalize within the structure.

Eisboch

We picked apart 5 failed cages of various vintages and none of them
seemed to "blow out" the screen before the structure failed. The only
real commonality was in every case there was an apparent failure of
the cables in the section that failed first. Once one part fails, the
rest comes down fairly fast if the wind keeps blowing.
The "flat spline" patio material will hold screen until the screen
itself fails. Round spline will pull out but that is not used here
except in door and window frames.
It is ironic that the old method of through bolting an eye bolt for
the cable stay seems more robust than the new style angle corner
bracket with 8-10 screws in it. The bracket itself fails. (all of the
new cage failures)
After this, I did add some additional cable stays to my cage and used
the eye bolt method. Wilma didn't hurt it.
After Charley we found a 40' mango tree on our cage, the oldest part.
I was amazed it didn't come crashing down but everything was in
compression and that is not the force that pulls them apart.
I ended up having a crane remove it (handy to have a wife in the
construction biz, his number was in her NexTel)- Hide quoted text -

- Show quoted text -

Usually, the greatest pressures in a wind event are the negative
pressures at the corners. Let's say the wind is blowing on the front
of a house. The back corners act like a wing and accelerate the wind.
Those leeward corners are where the negative pressure is the greatest.
I don't know how many times I've seen mobile homes on the highway
where the siding was being blown off, and always on the rear edges.