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# More Wind Stuff - Canopy Wind Loading/Recurrence Interval

• To: <seaint(--nospam--at)seaint.org>
• Subject: More Wind Stuff - Canopy Wind Loading/Recurrence Interval
• From: "Bill Polhemus" <bill(--nospam--at)polhemus.cc>
• Date: Thu, 18 Jul 2002 16:15:16 -0500

I'm having a difficult time designing a canopy at the entrance of a mall
building. In form it is simply four posts with a gable roof. I'm making the
structural system out of CFS, and it has cladding such as stucco or EIFS and
a steel panel roof.

The problem is that the wind load calculated from ASCE 7-98 kicks this
thing's butt.

Since the canopy is right up against a building, I'm using the "partially
enclosed" option. There is a TREMENDOUS amount of uplift, though, such that
the windward legs will see almost 10,000 lbs of uplift EACH! This is just
going to be ridiculous for the foundation design, which is going to have to
be drilled shaft footings if these forces are rational. I'm sure these folks
are NOT going to want to call out a foundation crew just for four footing!

In addition using the CFS is giving me outrageous lateral wind deflections.

So my questions are these:

1. What if any special allowances are available for a small stand-alone
canopy structure like this? Use a lower exposure factor? What? The ASCE 7
code is silent on this score.

2. Instead of the 100 year recurrence interval for determining the
deflection (which if I understand the ASCE 7 commentary, is what is used
along the gulf coast in order to generate the wind speed contours), may I
use a lower interval such as 25, 30, 15, even 10 years? If so, where would I
go to figure out how to adjust the wind speed for a different recurrence
interval?

As it is, I may have to rely on the existing structure for lateral support,
and that will mean lots of field measurements, etc. This was supposed to be
a quick 'n' dirty job, but I'm find it to be mostly just "dirty".

Any comments would be appreciated.

William L. Polhemus, Jr. P.E.
Polhemus Engineering Company
Katy, TX, USA
Phone (281) 492-2251
FAX (281) 492-8203
email bill(--nospam--at)polhemus.cc

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