At 02:32 PM 7/9/03 -0700, Jim Lux wrote:
>Stiffness isn't necessarily related to strength. Properly engineered
>structures have some amount of flex built into them. Changing the
>relative stiffnesses of structural members can change the distributions of
>the stress, and one of the challenges of structural engineering is
>distributing the stress appropriately. You'd much rather have the strain
>energy in something that is designed to take it with elastic deformation
>(i.e. springiness).. the tower in this case, which takes the strain by
>deforming (bending).
Jim's right, of course. I was thinking of the guyed tower study on K7NV's
Yagistress web page. Kurt used finite element analysis software and a
model of Rohn 45, if I remember right, and ran a series of cases. In at
least some of those, it was highly desirable to limit deflection at the
upper guy points, because not to do so risked exceeding the limits of lower
sections, particularly when the bottom section was embedded in concrete.
73, Pete N4ZR
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