Ned Simmons wrote:

snip

Case 3e, Chapter 5, Roark's 6th edition - concentrated
moment on a simply supported beam. The angular deflection
at the end of the tube adjacent to the triangle is .0188
radian = 1.08 degrees; .68" deflection at the winch's
attachment point 36" from the vertical tube.

Hi Ned,

When I read your post, at first I disagreed with you, then I agreed, and
now I partly agree. After some thought I am of the opinion that neither
of us have got it quite right.

My cantilever would be fine if the horizontal member was attached half
way up the vertical member, but the model becomes less accurate the
further it is moved from this position. Your model is fine in the
absence of the diagonal tension member (Steve's flat bar). With the
tension member present it isn't a moment which is applied to the
vertical member, but a point load instead.

I did some sketches and free body diagrams:

http://www.mythic-beasts.com/~cdt22/davit_calc2.jpg

I now think that the correct model is a simply supported beam under the
action of a point load F, where F is applied distance A from one end and
B from the other. In this case F = 3W, where W is the load on the
suspension point, A = 14' and B = 1'. What do you think?

I don't have a formula for this case. Perhaps if your book gives a
formula for this case, giving the deflection of the point at which the
load is applied, you could run a quick calculation and get an answer for
Steve? My guess is that it will come out with an answer a good bit less
than my original suggestion of 8", but I'd be interested to know.

I suspect that whatever model we use, we aren't going to get much closer
than an order of magnitude figure unless we know exactly how Steve will
construct it. Nevertheless I believe it would be wise to avoid putting
the long vertical member under a bending load.

Best wishes,

Chris