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# [SEAOC] Re: [SEAOC] Wind Pressure Coefficients (Cq)

• To: SEAOC(--nospam--at)power.net
• Subject: [SEAOC] Re: [SEAOC] Wind Pressure Coefficients (Cq)
• From: "Drake, Rick" <rick.drake(--nospam--at)fluordaniel.com>
• Date: Sat, 10 Aug 1996 11:05:00 -0700

```     The values for open frame towers come from ASCE 7, the source
document
for the UBC wind provisions.  The values reflect the density of
the
diagonal and cross-members of a typical tower, and are based on
wind
tunnel testing at the University of Western Ontario.  The values

probably seem high because each individual member is capable of
receiving a positive pressure on its windward side and a
negative
pressure on its leeward side.  I also suspect that the structure
as a
whole interrupts the wind field more as a solid object than as
an open
structure.

You might check out ASCE 7-95 to see if any of the wind
coefficients
provided are for structures more similar to yours.  Be careful,
ASCE
7-95 defines wind velocity in 3-second gusts, not the
fastest-mile
wind velocity in the UBC.  You'll have to convert to use ASCE
7-95.

Rick Drake, SE

_________________________________
Subject: [SEAOC] Wind Pressure Coefficients (Cq)
Author:  seaoc::(SEAOCAB) at ~FABRIK
Date:    8/10/96 9:15 AM

From: seaoc(--nospam--at)power.net
Date: Sat, Aug 10, 1996 9:15 AM
Subject: [SEAOC] Wind Pressure Coefficients (Cq)
To: seaoc
Can someone explain why the wind pressure coefficient (Cq) for
Open-Frame
towers (UBC 94) is so much higher than other structures?  According
to UBC 94
Sec. 1621, Open-Frame Towers are "Radio towers and other towers of
trussed
construction ..."  I suspect shape factor of assembled trusses has
something
to do with it.

Secondly, I am designing 60' tall x 15' sqaure open tower, assembled
with
four steel tube columns at the corners and connected at the top with
steel
tube beams.  No diagonal members in between the columns; just tall
free
standing columns.  What Cq factor should be used?

...
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Subject: [SEAOC] Wind Pressure Coefficients (Cq)