# 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 13:16:55 -0700
```-----Original Message-----
From: Davis Parsons [mailto:dparsons(--nospam--at)msc-engineers.com]
Sent: Friday, June 22, 2001 1:13 PM
To: seaint(--nospam--at)seaint.org
Subject: Re: Allowable Compressive stress-ACI 530

David Williams wrote:

> 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
>>
>>

>From the Masonry Designers' Guide for 12" CMU

>Face shell mortar bedding r=5.08 in.
>Full mortar bedding r=4.29 in.

--
>Davis G. Parsons II, PE RA AEI
>a practical structural engineer
>in Fort Worth, Texas

--
Without any grouted cells though...

Nick B.

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