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RE: ASCE 7 Wind Loads on Bare Steel Framing - Opinions Wanted

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The drag coefficients developed in the ASCE Wind Loads and Anchor Bolt Design for Petrochemical Facilities should still be valid.  However there have been many advances in wind pressure development including the wind velocities.  In the ideal world, we would have an updated version of the ASCE Wind Loads and Anchor Bolt Design for Petrochemical Facilities.  However, we are not there yet.  I would opt for a blend. 
Remind your colleague about the difference in the fastest mile vs. the 3 second gust change that happened with the ASCE 7-95. 

Regards, Harold Sprague


From: bill(--nospam--at)
To: seaint(--nospam--at)
Subject: ASCE 7 Wind Loads on Bare Steel Framing - Opinions Wanted
Date: Wed, 4 Mar 2009 09:07:38 -0500

Lots of pipe racks to look at. Very fascinating.
(P.S. Not really).
Years ago when the ASCE 7 standard was focused almost exclusively on building structures, we used to have rules of thumb for applying wind loads to these kinds of "lattice" structures like pipe racks and large structural steel bare frames. There were all sorts of arguments about "shielding" of one member from another, for example.
ASCE published a guideline back in the 90s ("Wind Loads and Anchor Bolt Design for Petrochemical Facilities") to help establish some consensus regarding how to apply loads to these structures. It was based on the state of the art at that time - ASCE 7-93 or -95 IIRC - which of course has changed quite a bit since then.
ASCE 7-05 was significant in that it added quite a few commonly-seen but previously unaddressed systems, like canopy roofs and braced steel towers, to the provisions for calculating wind loads. But there are still some questions in my mind at least.
It seems easy enough to apply provisions for "Open Signs and Lattice Frameworks" (ASCE 7-05 Fig. 6-22) and "Trussed Towers" (Fig. 6-23), for example, but it is NOT obvious that these are correct.
It seems to me that a colleague and I did a comparison with the ASCE "Petrochemical Facilities" publication procedure, and ASCE 7-05 using Fig. 6-22, and it came pretty darn close. I have been a proponent of going with ASCE 7-05 but I have "older" colleagues who don't much like change, and insist that since the older ASCE "Petrochemical Facilities" publication was good enough "then," it should be good enough now.

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