Bill,

I feel I must enter this thread one more time.

What about the vertical component of the tension in the beam FBD on
the left?

We can't include it as we know nothing about the kinds of joints
Steve intends to employ in the structure. I assumed that there are
pin joints at each end of the beam because this makes the structure
statically determinate. We know so little about the structure that
this is only assumption one can make. Granted, I did not draw a pin
joint. That was an honest mistake.

Amid your stream of criticism and confusion between horizontal and
vertical, I gave the answer to a different question: the question "Why
is there no vertical force shown on the left-hand FBD acting at the
junction of the horizontal and vertical members?" I stand by the answer
I gave to this question. The answer to your question is very simple. I
believe the free body diagram on the left to be complete and correct. No
horizontal force is shown acting on the top end of the beam because the
upper support provides a reaction against this (see the roller support
in my diagram). If you disagree with this, please elaborate.

You called it a tension member, hence you were
assuming frictionless pins and negligable weight. Otherwise known as
a two force member, and it's item one in any engineering statics course.

I agree with your description of the tension member. I don't see what
you're complaining about here.

snip

As has been demonstrated, one of the problems with your proposed
structure is that it isn't as simple as it looks. Its behaviour
is more
complicated and less easy to predict than I thought, and probably than
Ned and Bill thought, too.

Speak for yourself. You haven't come close to the complex part
(searching for the weak link in the chain so to speak). The deformation
analysis is at the level of an undergrad homework problem.

If it's so simple, I still don't understand why you don't go ahead and
solve it. From my recollection of undergraduate structures questions,
this might have been a difficult second year "bonus" question. The kind
which looks simple but isn't. We are also presented with the problem of
having to model a vague structure from scratch; we haven't been given an
idealised structure on which to perform the mathematics.

I would attack the
problem by making some changes to the design (you should still be able
to use the materials you've bought) rather than trying to find someone
who's a professional structural engineer.

More bad advice.

Why? Steve is unlikely to hire a structural engineer. Some structures
are easier to analyse than others. Some structures are designed so that
their behaviour is easier to predict. I've seen older bridges which are
built with a roller support at one end. Why? So that the structure is
statically determinate and easier to model. Changing a design so that
its behaviour is more predictable is a sensible thing to do. If you
disagree with this, please explain why.

To the group at large, I offer an apology for the nature of this
discussion, but I have learned to respect you. To not point out the
flaws would be unfair to you, and potentially dangerous to the OP. I
trust you will do the same should anyone give me bad advice about
clamping or feed rates.

You seem devoted to accusing me of offering bad advice without
explaining why my advice is bad, or attempting to offer better advice of
your own. Your refusal to solve what you claim is an easy problem is, to
me, suspicious. It's all too convenient. The risk involved in offering
Steve a solution is not great. You're not a practising structural
engineer, so you needn't worry about your reputation, and if you say
that your advice is offered without warranty I don't believe you have
any legal worries. The risk doesn't concern me, and it doesn't appear to
concern Ned either.

I tried to shed some light on Steve's problem in good faith. Perhaps the
model I proposed was somewhat flawed, but you just comdemned it as
"nonsense". At no point did you attempt to explain why it was nonsense,
or how I might refine the model to give a better answer. You never
explain why my advice is "bad". Furthermore, some of your questions and
comments barely make sense.

I'm of the opinion that you're attempting to make me look a fool, and I
don't appreciate it. An engineer contacted me by e-mail this afternoon
and offered some suggestions about how to refine my model. Why didn't
you take this approach?

I am also intrigued to learn that you work in an anaesthesiology lab:
http://needle.anest.ufl.edu/anest4/bills/

Chris