Bill Schwab wrote:
Chris,

I fear you are mixing models in a way that does not work. You
compute support reactions based on the ends being fixed horizontally,
and then model the deflection based on a cantelever beam.



The cantilever beam only represents part of the vertical member: the
14' from the horizontal to the ground. I have made an imaginary cut
14' from the ground. This point can move horizontally, but has a
moment and shear force applied to it. With a bit of spatial twisting
and turning in my mind, I believe this 14' section can be modelled as
a cantilever. The fact that the root moves horizontally while the tip
is fixed doesn't matter.


That might end up being true, but I do not think you can hand-wave it
that way. With its max deflection somewhere in the middle of the beam,
it is more likely that it will function as two half(more or less)-length
cantelevers, which puts quite a hurt on the cubic term in the deflection.

I take your point here. The root of the cantilever may rotate a bit so
that the maximum deflection is somewhere in the middle of the beam. But
I believe that the cantilever model will give a useful result for a
10-minute, one-side-of-paper calculation. Whether it is more like a
single cantilever or two half-length cantilevers will depend on Steve's
joints and anchor points. When we know so little, there will inevitably
be some hand waving. I still think it's a fair model based on the
information we have. It is only intended to give an order of magnitude
result.

Chris