welded aluminum walkway simulation

Well I can maybe save you some time there then because a Beam analysis will not take into account how the ends are welded together.  It just assumes they come together at a node.  You can refine the connection at the node some but you cannot do any kind of weld analysis at the node.  Beams is a very simplistic way to view a model and is more for gettingquick results over large truss like structures.  If you want detailed weld analysis I know there is a feature in 2011 (and I assume 2012) that allows you to define a weld between two bodies and then do an analysis strictly on that connection, however, the pieces must be defined as shells I believe.  I have not been able to use this feature since I am still stuck using 2010 thanks to corporate bureaucracy.  Plus I am not sure how well it would work in a larger structure such as yours.  If you want to look more closely at connections in particular you can treat all bodies as solids and add features to mimic your welds but that can be pretty time consuming.  You can also choose one connection and model it separately and then run an analysis on it by itself using forces determined from an analysis of the structure as a whole.  Hope some of this helps.

Ryan W.

Hey Dave,

Ryan is on the ball. You use the beam analysis to get the loads at the joint. You should also know that SWX beam analysis is not their strongest suit by a long shot so ensure that you believe your analysis results. Many people have found many issues with this aspect of the code. Since it sounds like people could get hurt or killed be sure the analysis is good enough and you understand what's up. With that said, find the joint with the worst loading - these will be resolvable on beam center lines then make a free body diagram of the joint and figure out the loads in the welds and use a manual method to assess the welded joints. The welded joint function Ryan has mentioned has also had its share of issues - like bad results at non normal angles. No idea if it has been addressed yet or not. You could do a solid analysis on hte joint but again be judicous in asssessing the results though this aspect of the code tends to work pretty well. These analysis need to be done with some care in set up and interpretation.

No idea what you mean by "only on the side faces" but in general you want the welds loaded in shear and not in tension with throat depths and lengths sufficient to get the job done, Given this is aluminum - not sure which one but in the welded state it may have substantially reduced strengths in the as welded condition. And fatigue of welded Al joints is also something to pay attention to. You are going to want to aim for stress in the welds in the very low 1000's of psi or less depending on what the material is, how long it is supposed to last, what the load spectrum is and other things. You might want to consider a marine alloy in the 5000 series for corrsion and weldability . Good luck.

Dave, what are you setting your mesh size and tolerance to?  That was the only thing I changed when I ran my analysis.  Using solids you will almost always have to make the default mesh size finer, especially when working with multi bodies.  It takes some trial and error to figure out what numbers work best with each model.

Ryan W.

You are correct Bill, and I agree about the accessability, my post was poorly worded.  I think FEA does need to me more accessable in general, especially with the more advanced packages.  That said, however, I have found that if a user is working with an advanced package, they more than likely have a good understanding of the theroy and general good modeling practices (yes, it's a stereotype).  I have seen a lot of bad analysis performed in SolidWorks and similar packages because they are so accessable, which allows users, who do not have enough experience, to easily run a bad analysis and believe the results are good.  Sure, this isn't the fault of the program so much, it is the fault of the user, but I see it all the time.  It isn't always an engineer doing this; it can be a draftsman, or general designer that is using FEA.  It's perfectly OK for them to dabble with it and learn, and I encourage that, however, basing design decisions on the results without fully understanding them or how they came to be is asking for trouble.  I see this all the time. 

I would really like to see SolidWork have messages or similar that help to give good suggestions for modeling and keep people on the right track, but I doubt we'll ever see that due to legal implications...  There are some features that have no business being there too; look at the "Mesh and Run" option.  This defaults to whatever mesh settings SW thinks your computer is capable of (more often than not, bad settings) and produces a result!  The mesh is one of the most important aspects driving the solution, bad mesh, bad solution.  When you allow a user to mesh and run, you remove the opportunity to review the mesh, check for bad elements, etc. and get them a result.  This was a poor call on SolidWork's part, all to save a mouse click.  SolidWorks is by far not the worst package from this respect, though, I've seen packages where you can't ever view the mesh, you have to trust that is was done right! 

You say "from a philisophical perspective any analysis is better than no analysis - just respect what you don't know", which I completely agree with provided that the user respects what they don't know.  I see so many examples where the user did not respect what they didn't know, many times because they didn't know what they didn't know.  This is where I see room for improvement in increasing the accessability of the simulation software. 

Dave, please don't be detered by my posts, you obviously are respecting what you don't know, and are here willing to learn, which is fantastic.  We all started out at some point with no idea of what we're doing, and you're on the right track.