BA..... I believe you are right. We don’t often disagree on much, but when we did a second time, I thought I better restudy my FBD on paper, and my entire thinking on the problem, rather than just imagineering it. Thanks.
BA and I were trying to offer the OP’er. a fairly clean and simple approx. method for looking at his problem. At one point in time, us older fellows learned, used and only had these methods of analysis. But, through that training and usage I think we developed an intuition and understanding of structures which is missing from the training today. And, these methods are usually our first step in looking at almost any problem. We can always make it more complex later, and more often than not someone else does that for us. As the OP’er’s. problem became more complex: i.e. different t&b chords in strength and stiffness; existing diag. members and their welded joints, rather than verts. and Tee joints; useless added verts. and a willingness to let the bot. chord develop plastic hinges and just become a tension link; I was about to write that this problem should ultimately be done with a computer program to actually hone in on member forces and moments, for the deflection, and because there were many joists involved. Many of the secondary issues can probably still be handled by engineering judgement and experience rather than FEA and VonMises stresses. ToadJ beat me to that, and then beat me with it.
I am certainly not against the use of computer software to assist us in doing our structural analysis, in fact they are essential today. What I rail against is turning to them as the very first step in the problem development and solution, and because the designer (engineer? or computer runner?) has so little real understanding of structures that he/she has no other recourse, and then doesn’t really understand the output either, for the same reason. If they don’t start with some structural intuition, I don’t know how they make the proper input decisions, and many of the OP’s show this. I think the guys/gals who do some hand calcs., simple FBD’s and that sort of study to start using the programs, and then do hand calcs., and various quick checks of the computer output are on the right track.
These may be the final flailings of an old dog unable to learn new tricks. I actually think I understand most of the tricks, I just don’t know if I have enough years of engineering left to become proficient at the tricks. Given the use I would put them to, I really can’t afford the latest software, I can’t keep up with the rate of change, and they have become so complex to use, in trying to do everything under every possible set of conditions, that I have to relearn every time I try to use them, they are no longer intuitive to me, nor are they less time consuming. I was actually a pretty good programmer and computer user for engineering applications from the mid 60's - mid 70's, got away from it for a while and it passed me at the speed of light. I would love to have some of you young people working with me. Gosh, what I could learn from you, maybe teach you a little too.