# [TowerTalk] Mast Stress Calc

John D. Farr johnfarr@ro.com
Thu, 17 May 2001 17:59:17 -0500

```This is absolutely true, but if you fasten them together at intervals it
becomes much stronger.
gl
John KC4ZXX

-----Original Message-----
From: owner-towertalk@contesting.com
[mailto:owner-towertalk@contesting.com]On Behalf Of Kurt Andress
Sent: Thursday, May 17, 2001 2:57 PM
To: Sylvan Katz; towertalk
Subject: Re: [TowerTalk] Mast Stress Calc

Sylvan Katz wrote:
>
> GM TT's
>
> If I place one piece of steel pipe inside another piece of steel pipe to
> reinforce a section of mast is the moment of inertia of the reinforced
> section determined by adding the moments of inertia of the individual
> pieces? How do I calculate the yield strength of the reinforced section of
> mast? Is it the sum of the yield strengths for the individual sections?
>
> tnx .. sylvan
>

The moment of inertia (I) of the two tubess can be added together as long
as they have the same elastic modulus (I.E. both steel tubes).

The bending stress formula F=MC/I calculates the stress on the outer
surface of the section (C=the radius of the tube OD), so use the yield
strength of the outer tube. It's outer surface is where initial yield will
occur, after that it is sure to only get worse so the yield of the inner
tube is not so important.
The benefit of the inner reinforcment is its contibution to I. If I is
doubled, stress is halved.

--
73, Kurt, K7NV

http://yagistress.freeyellow.com

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