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RE: ASCE 7-02 Enclosure Classifications

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I have had this conversation with Jon Paterka of CPP. He is on the ASCE 7 wind committee. Jon told me that it was the intent of the code to characterize the high probability that the windows would be broken out in ANY or all walls during a hurricane. This would likely significantly increase the loads on the walls. Basically, if the windows are not impact resistant and you have not provided for some sort of storm covering, all of the windows without impact resistant glazing should be treated as openings.

This was watered down considerably from what was intended from the original authors of the provisions in the Standard Building Code. This provision was a result of some typhoon studies in Australia and Hurricane Andrew meets Dade County. The provision for the plywood covering was not what the code developers wanted. But the developers did not want to provide the very robust glazing required for wind borne debris impact resistance.

Regards,
Harold Sprague




From: "Rob Still" <robs(--nospam--at)adcengineering.com>
Reply-To: <seaint(--nospam--at)seaint.org>
To: <seaint(--nospam--at)seaint.org>
Subject: ASCE 7-02 Enclosure Classifications
Date: Thu, 3 Feb 2005 09:25:59 -0500

To all,

I'm hoping to solicit opinions from fellow engineers and possibly any
ASCE Committee members that the list may be distributed to regarding
ASCE 7-02 and the Enclosure Classifications as it relates to Partially
Enclosed and Enclosed.  We are currently having a lengthy debate in our
office (Charleston, SC) regarding both the letter and the intent of the
code specifically section 6.5.9 and its subsections.  The heart of the
debate lies in the use of impact resistant glass in hurricane regions.
Section 6.5.9.3 requires that all glazing in hurricane regions shall be
impact resistant or protection (operable shutters or plywood panels) be
provided.  The Exception below, however, allows non-impact rated glazing
to be used if the "unprotected glazing that receives positive external
pressure is considered an opening."

So herein is our crossroads.  If "Positive External Pressure" is related
to each specific load case generally there is one wall which receives
positive external pressure.  This would mean that if non-impact glazing
is provided and only one wall has glazing considered as openings (the
other 3 walls with non-impact rated glazing are not receiving pos ext
pressure so not an opening) then the building would nearly always be
considered Partially Enclosed.

The other side of the coin is if the "Positive External Pressure"
statement is really intended to mean at any point during loading then
one would assume that each perimeter wall would have openings.  Assuming
the openings are symmetrical and evenly dispersed the building would be
classified as Enclosed.

I have several other questions in this area, particularly the
commentaries description of operable windows and doors as openings that
seem to muddy the waters even more, but if I could at least get some
opinions regarding the overall question first I would be much
appreciative.

Thanks in advance,

Rob Still, P.E.
ADC Engineering, Inc.


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