Simulation with welded frame question

• I'd use weldments (beam elements) and run a buckling analysis.
• If the table is a frame, you simply draw a wireframe (line drawing of the frame). You then create your cross-secitons for each unique member type (if you only have 1 type of cross-section, then you only need 1 profile). You would then apply the cross-section(s) to the appropriate lines in your wireframe drawing.
• NOTE: for a buckling analysis you have to specify a force. With that said, you should determine what kind of forces you are expecting (worst case scenarios) before modeling the problem. Another way to approach the problem is to do a stress analysis with these determined loads and see if the stresses are beyond yeild. (This approach is a bit more common because, with tables, the legs are typically short compared to the other dimensions and buckling doesn't really happen before the welds break or the surface collapses. Although, if you have thin legs, you might see buckling first. As far as the welds failing, you can specify those parameters and apply specific yeild values to your joints. You could always model the table without these details and observe your peak stresses at the joints.
• For the boundary conditions, I'd use a pin for 1 leg and rollers for the other 3 legs. A pin boundary condition eliminates vertical and horizontal motion in a given plane, but allows for rotation. A roller eliminates vertical displacement and allows for both rotation and lateral motion in a given plane. Essentially, all of your legs would be fixed onto a plane, but three legs would be allowed to slide away from the leg with the pin joint. I do believe this configuration is sufficiently constrained. One thing to note, a single column with pins on both ends produces the smallest critical load for buckling. Typically it takes a larger force for a fixed end condition column. In otherwords, you are adding to the factor of saftey by modeling with pin joints.
• Another configuration I would try would be 1 fixed-end boundary condition on 1 leg and rollers on the rest. You can change the boundary conditions very easily and re-run the simulation. Your report could discuss the effects of the different end condtions and perhaps use the lowest quantity as your safe value.
• I would not consider friction as it adds an unnecessary complexity to the problem. Just remember, for tables, it's pretty uncommon to design things really close to the point of failure. You would want a pretty decent factor of saftey, right?

good luck : ]

the only time the weight on the table (the 200 lbs and whatever is sitting on it) matters for a collapse scenario is when there is sufficient bending in the legs which then allows a moment arm to bend the leg further. If you want a detailed analysis, maybe you could do the solid element analysis (shown in the second picture) with a high mesh concentartion around the joint and apply the load shown and also apply a load of 200lbs in-line with the leg. One thing that i do want to stress is that you not be overly concerned about modeling the weld. I think a basic stress analysis at the joint will reveal enough information. If you have reinforcements at the leg joint (like a 90 degree bracket), it'd be difficult to model the problem with beams. You would probably need to do solid elements (in which case you would only model 1 leg and a section of the table, which you would have to deem sufficiently large to keep the effects of the BCs away from the stress concentation).