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RE: ASCE 7-95 question...

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Title: RE: ASCE 7-95 question...

One thing to keep in mind, if your building is 60 feet or less, you are not forced to design the main force resisting system as a "low rise".  You are permitted to use figure 6-3, and design it as a building of "all heights" (non-low rise).  I find Fig 6-3 easier to work with than Fig 6-4, so I design all of my low-rise buildings this way.

As for a reason why the coefficients are not equal, maybe it has to do with the wind component that is coming in from the skewed direction (fig 6-4).  Fig 6-3 only has wind in the directions of the principal axis. 

Some FYI: in ASCE 7-98, Fig 6-4 is tabled the same as 7-95.

I have never sat down and compared the results of fig 6-3 to 6-4.  Does anyone know if the results vary significantly between methods?

John Connor, PE
Kansas City, MO



-----Original Message-----
From: Scott E Maxwell [mailto:smaxwell(--nospam--at)engin.umich.edu]
Sent: Wednesday, July 19, 2000 3:11 PM
To: seaint(--nospam--at)seaint.org
Subject: ASCE 7-95 question...


I have a question for anyone out there who is familiar with ASCE 7-95.  I
am computing the main wind force loads for a building that is under 60 ft
(low rise).  So I am using ASCE 7-95's "low rise" method.  I am in the
process of determining the External Pressure Coefficients (GCpf) per
Figure 6-4.  I am looking at CASE A.  My roof slope is 0 degrees.  So per
Figure 6-4, the coefficient would be -0.69 for zone 2 (windward roof) and
-0.37 for zone 3 (leeward roof).  Now this does not make sense to me.  If
my roof is flat (i.e. 0 degrees) shouldn't both of these coefficients be
the SAME?  This is not consist with the method for non-low rise buildings
(the cofficients are the same for roof with 10 degrees or less).

Also, another dumb question...how does one obtain a roof with a slope of
90 degrees?  <grin>

Thanks,

Scott Maxwell, PE, SE