On Sep 20, 9:50*am, "Eisboch" wrote:
wrote in message

...
On Sep 19, 10:00 pm, JimH wrote:

What an idiot. In the first place, structures aren't "rated" for a
particular wind speed.

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Really?

I was under the impression that building codes, particularly in Florida,
have specific requirements on wind speed ratings.
Newer codes are higher than those of 20 years ago.

I know that when we decided to add an aluminum framed, screen enclousure on
the pool we had beside the Florida house, we ran into a bee's nest of
permitting regulations and requirements. *In order to have any part of the
enclousure attach to any part of the house or deck, we were required to get
a professional structural engineer, certified in Florida, to approve it,
including modifications required to ensure that the method of construction
and attachment met current codes. *The criteria was wind speed, and I
believe at the time it was 150 mph. * This was in addition to having the
screen enclousure frame itself to be designed to 150 mph wind.

They didn't care about the screening .... in fact it is designed to blow out
at a certain wind speed, reducing the sail effect on the aluminum frame.

Eisboch

While a structure is designed using specific wind data, in Florida's
case, the FBC basically the IBC with amendments, and the IBC uses ASCE
7-05 which most building codes use, and those wind maps are based on
100 year data. BUT a structure isn't "rated" by anyone, unless a
private entity, say the builder, decides to do so to make a selling
point. Here is why. Let's say we have a wind of a certain speed and a
certain direction blowing on a rectangular building. Even though the
speed is constant (here's where we show Harry and JimH don't know
****~!) the wind PRESSURE is NOT constant. Have you ever seen a mobile
home on the side of the highway where part of the siding has blown off
when towing? Notice where the siding fails nine out of ten times. The
rear corner. Negative pressure from the wind coming around that corner
has sucked the siding off! In short, the windward wall has a postive
pressure of X amount, the leeward wall has a negative pressure of Y
amount, they are hardly ever the same value. Then you have the roof.
Slope, wind direction, area, etc. all have an affect on the PRESSURE.
In short, we are really designing for this negative and positive
pressure as opposed to wind speed. We simply use data in the form of
wind speed to mathematically arrive at those pressures. And it goes
further, terrain makes a big impact, as well as nearby structure.