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## [TowerTalk] Multiple-layer stress modulus???

 To: [TowerTalk] Multiple-layer stress modulus??? w8mm@ibm.net (Mike Valentine - W8MM) Wed, 07 May 1997 14:40:24 -0400
 ```Hello all! In a effort to reduce the weight of a mast for my antenna project, it would be desirable to use a light-weight mast that is reinforced with an interior cylinder or rod in the lower portion where the moment is greater. A constant outside diameter makes boom-to-mast clamps easier and provides a bigger "grip diameter" for the top-most antenna, although the mast self-load from wind pressure is a tad higher compared to a conventionally tapered mast. My question: Does one merely add the section modulii for the mast and the reinforcer to get the composite stress result??? I did some preliminary calculations for a 2"O.D./1.75"I.D. mast with the addition of a 1.75"O.D./1.5"I.D. reinforcer that actually looked stronger by a small amount than a continuous section of 2"O.D./1.5"I.D.. That got me thinking that my assumtions might be out in left field. For 2"O.D./1.5"I.D. -> pi((2*4)-(1.5*4))/32(2) = 0.537 in*3 For 2"O.D./1.75"I.D. -> pi((2*4)-(1.75*4))/32(2) = 0.325 in*3 1.75"O.D./1.5"I.D. -> pi((1.75*4)-(1.5*4))/32(1.75) = 0.242 in*3 Sum of modulii = 0.325 + 0.242 = 0.567 0.567/0.537 -> 5.6% improvement from taking it in two layers??? Weird, eh? What am I doing wrong here?? Mike - W8MM - EM79sd -- FAQ on WWW: http://www.contesting.com/towertalkfaq.html Submissions: towertalk@contesting.com Administrative requests: towertalk-REQUEST@contesting.com Problems: owner-towertalk@contesting.com ```
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