I'm trying to do some calculations for a personal project. I'm trying to understand column strength / buckling. My questions relate to Effective Length Constant, which is based on Boundary Conditions (how the ends of the column are restrained) The four choices there are: Free, Fixed, Guided or Pinned:

Here's a sampling... Sampling of End Conditions

And different end conditions affect the Effective Length Constant, used in buckling calculations:

Effective Length Constants

(edit.. ref: source for the above Length Constants)

But my dilemma is I'm intending welded metal tubing without corner gussets. I think with a gusset (and / or with cross bracing straps), I'd use Fixed-Fixed calculations, but simple butt welds that's not so clear.

Does anyone have testing data or other experience on how to address end conditions for buckling calculations with a simple welded butt joint at the ends of a column under load? <---- Here is my question for this posting...

And just for reference, the kind of thing I'm investigating is a drive on vehicle ramp. Obviously lighter is better for handling and storage... And yes I'm thinking astronomically large safety margins, but I'd like to know the real load capability numbers.

Note: related reference.

Again, how does one address end conditions for welded in place column materials?

  • 1
    $\begingroup$ For a structure with many columns and "stiff" lateral connections between them, Euler buckling is such a crude approximation that worrying which boundary condition to use is entirely theoretical, because there is no way that one column can buckle in isolation from all the others. If you really want to estimate the buckling load, you need to model the whole ramp and do a Finite Element analysis. The answer will depend on the position of the load from the car wheels, of course. $\endgroup$
    – alephzero
    Commented Nov 21, 2019 at 21:07
  • $\begingroup$ Your table of k factor for effective length is wrong. But your issue is not buckling. It is just crushing if anything and as you worry about breaking of the welds. This is one of the times that just copying the photo you linked may be the shortest answer. I bet you can even find them on the internet very easily. $\endgroup$
    – kamran
    Commented Nov 22, 2019 at 3:42
  • $\begingroup$ @kamran I believe you were referring to the Effective Length (C) factor (and not k, Radius of Gyration) I edited the original to include source link of those values. I didn't make them up. And as for just copying designs of others on the internet.. Hmm.. Are those optimal designs? (required safety, required strength, minimum cost, absolute minimum weight?) How do you know? I saw this comment recentlyYour table of k factor... is wrong that reminded me that not everything you find on the internet is great. $\endgroup$
    – zipzit
    Commented Nov 22, 2019 at 6:20
  • $\begingroup$ Note: i will say, after writing this question, I started doing analysis with different materials and column lengths. I was surprised as to how strong these materials are in column strength below 20" in length. The finite element analysis suggestion makes sense, I just have to brush up on my Solidworks FEA stuff. $\endgroup$
    – zipzit
    Commented Nov 22, 2019 at 6:24


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