Rfreund:
A sketch of your actual connection would be real helpful, otherwise your OP could probably describe at least several dozen slightly different details; all of which might be treated slightly differently, in their stress analysis. There are some very good trains of thought in the other thread, which you participated in briefly. I am at a distinct disadvantage in some of these discussions because people keep referring. to a page and formula number in the latest ed. of codes which I may not have a copy of. I do wish people would give the formula or quote the para., but that may be much more than I have a right to expect; I could buy the newest code too if it would make any money for me, instead of just cost me to play here.
I believe Lion’s main idea, in the other thread, was to design one part of the joint for the shear loads, and one part for the tension or bending loads and then let them coexist. They will share all the loads on the joint, and exactly how, we might never know. WillisV suggests that there may be a few cases on connection details where we might want to consider combined stresses, and I agree with him, then the trick is, when and where. But, then Thornton’s paper suggests this may be beating a dead horse, in most cases.
I keep harping on simple designs and clean details, and at the same time you should have a good feel for where some of these max. combined stress may occur, and knowing that at one corner they may be additive and at the opp. corner they may lead to a reduced max., but maybe never knowing their exact magnitude. Even with all the fancy computer software we have today our analysis is not an exact science, except on the very simplest of structures and connections, or you could spend the rest of your life designing a couple connections, maybe more exacter..., or not. Otherwise, the most important thing might be knowing where these higher stresses can occur, and detailing and welding in those areas to prevent any poor quality, stress raisers or hard spots which could lead to failure. Strain rate could come into play in a few instances like EQ events, and maybe fatigue in some cases, but most std. structural connections and stresses don’t fit these conditions. How you reinf. and terminate the end of a weld line where these higher stresses might occur may be more important than the exact stress magnitude, if you could pin it down. Certainly, you don’t want craters or undercuts at the ends of welds. You might provide a partial bevel at the last few inches, so that you end up with the typical fillet reinforcing the bevel and lowering the weld stress in that area. Be very careful about welding around sharp corners which almost always leaves an undercut notch in the corner material. Attention to these kinds of details may be more important than knowing the max. combined stress to some uncertain degree. Which is the biggest stress on the weld, worry most about that, how does it mistreat your weld?
Everyone is all worried about VonMise, but few people seem to know who he is or what he does, or why or if he is important. If, through your detailing, you are careful about where and how a little yielding or plasticity happens, and it is well protected by material, all around it, which does not reach yield, this is seldom a failure mechanism, and probably happens far more than we actually imagine. High stresses and the wrong orientation at the root of a weld can be disastrous. For the most part, I’ve looked at combined stresses and max. stresses when faced with fatigue problems, not static problems.
