Christopher Tidy wrote:
Bill Schwab wrote:

snip

My first model may have been fairly inaccurate,



tactOff
Chris, it was nonsense.
/tactOff


Bill, you have yet to propose a model of your own. You could have
proposed a model in the time you spent criticising mine.

Responsibility w/o compensation. Nice try, but I'm not going on the
record with a solution.


but that's the way it goes: you build one model, think about it and
discuss it, then build a better one.


Not in this case. You clearly lack understanding of the basics that
go into such a model.

An easy insult to offer, but as I asked, where is your model?

It is not an insult; it is a professional opinion.


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.



Again, nonsense. 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.


Consider my above answer retracted. Your question does not make it clear
which member you're talking about, and now you've changed the force
you're talking about from vertical to horizontal.

The identity of the member would be clear to an engineer; it would be
clear to just about anyone since I used the unique name _you_ gave it.
The h/v thing was a typo, no doubt the result of my distraction with
trying to find a nice way to put this.



So here we have three guys who know a little about structural
engineering having an argument. If we'd worked together we could
possibly have been helpful, but I do not believe we are helping Steve
now, so I will not continue this discussion.

I think you will find the level of knowledge of the "three guys" varies
just a bit. Hopefully the OP has figured out that your advice is not to
be taken at face value.


Toward taking my leave of this thread, I will address some of your other
comments here.

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.




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.


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.

Bill