# RE: Allowable Compressive stress-ACI 530

• To: "'seaint(--nospam--at)seaint.org'" <seaint(--nospam--at)seaint.org>
• Subject: RE: Allowable Compressive stress-ACI 530
• From: Nicholas Blackburn <nblackburn(--nospam--at)fdgoak.com>
• Date: Fri, 22 Jun 2001 13:08:41 -0700
```The radius of gyration is given in the UBC Tables 21-H-1, H-2 and H-3 for
different materials and sizes and %grouted cells.  If you don't have the UBC
available, send me a private email providing the size(s) and block
material(s) to be used and %grouted cells. Typical Concrete Masonry Units,
solid grouted 12" wide r=3.34 (r=sqrt(I/Aeffective))

Too bad you can't use strength design, much more efficient!

Nicholas Blackburn, PE
mailto:nblackburn(--nospam--at)fdgoak.com

-----Original Message-----
From: David Williams [mailto:dwilliams(--nospam--at)snydereng.com]
Sent: Friday, June 22, 2001 12:50 PM
To: Seaint(--nospam--at)Seaint.Org
Subject: Allowable Compressive stress-ACI 530

I'm designing a 12'-6" tall reinforced CMU wall using 12" block (actually
the wall is taller than that, but it'll have a lateral support @ 12.5').  I
have to use allowable stress design  (local building code requirement).
Equation 2-17 in subsection 2.3.3.2 is used to calculate allowable
compressive stress in the masonry due to axial loading.  The equation uses a
ratio of h/r which is the ratio of the effective height of the wall to the
"radius of gyration" of the member.

My question is: How is the radius of gyration to be calculated?  Is it the
height of the wall divided by the square root of 3?

TIA

David L. Williams, P.E.
Snyder Engineering, Inc.
Columbia, MO  65202

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