I’m siding with the bleater, while he may not know exactly how to express his position, that often happens when you have the blind leading the blind. The reactions are not all 1g, and if you are not working on a dynamic problem, get rid of the g and mass; the reactions are not all 1.0(wl) either. He is correct, because this is an indeterminate structure. And, we knew this long before you could get your hands on a FEA program. Several people have given you very good approximations for the various reactions on this indeterminate beam, assuming equal span lengths and uniform loading. That “These reaction forces are used to obtain the mass distribution of the structure.,” seems absolutely bass-acwards to me. In most structure’s, hear on earth, the weight () distribution of the structure and any superimposed loads dictates the reaction forces.
Seems like FEA programs and computers have made for some really dangerous engineering going on in the world these days. Someone who doesn’t understand how his FEA program works, its limitations and restrictions on its use, or how to model the problem he is trying to address, can plug a bunch of number in, and out pops some numbers, called answers or solutions, which no one seems to know quite how to interpret, and that’s called engineering these days. A FEA program does not an engioneer make. In fact, it scares the hell out of me, I could be standing under one of those structure some day when it fails.
Then we have this new phenomenon where we get together, in community or committee or as a team; communicate like hell and come up with a real democratic, politically correct, solution to the engineering problem. And, even if nobody on the team really knows how to get to the correct solution to the problem, it must still be better by committee, if we communicate long enough and hard enough, we can come up with a pretty good, although mostly wrong, solution to the problem. No matter how many people on the team think 2 + 2 might equal 5; and we even took a vote and 5 won; that won’t often be the correct answer, even though it is quite democratic.
You really need a local mentor for these types of questions, and he/she should know more about the subject than you do, so they can offer constructive, and correct, guidance. Together, you are both looking at the same drawings, specs. and initial data, and that person can get you started in the right directions, ask you leading questions, and tell you when you are getting off track. When you guys ask your questions on these forums, you rarely give enough info. for a meaningful response, we can’t see the drawings, the problem isn’t well defined, so you often get a bunch of fairly good best-guess answers, which would probably be helpful if you knew what parts to pick out of them for your particular use. But, given the fact that you don’t understand your own problem very well, it is unlikely that you will pick out the important, applicable, nuggets from the many answers. This forum is probably not the best place to be instructing people in the first few courses in strength of materials, theory of elasticity, structural design and analysis, or basic design in any of the building materials. They should go to college for that, get an engineering degree or a technicians degree, so they can truly start to comprehend the significant parts of the engineering problem they are looking at. And, this forum is not the right place to develop a basic understanding of the use of a FEA program either, nor will that program compensate for lack of basic engineering understanding of the problem.
I believe that the respondents genuinely want to be helpful, but as often as not they can’t, they don’t see the whole picture and can only give half answers, which might then be misused. It seems to me that at times, we are perpetuating, tolerating, condoning or encouraging, people who have no business doing engineering, to pretend they are engineers. Worse yet, they may be designing something which could really be dangerous, and hurt someone. “We’ve been using this method for years” might be a good answer here, particularly if none of them, whatever THEY are, have failed in the past. Because, there isn’t much evidence that this forum exchange is really leading to a better more accurate solution to whatever the problem is.
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