I have seen that steel columns in multiple story buildings span multiple stories, in that case how do you calculate the buckling length for the column? do you take the whole column's height, or just the story height? Or is it that beam connections define the points at which to take the critical length?

  • $\begingroup$ Generally connection points that reinforce against buckling will mean buckling is to occur between the points. Reinforcements need to be sufficiently strong compared to bear load that would otherwise cause buckling there so a calculation at 2x the reinforcement spacing can help determine whether that condition is met if you are sizing beams against a table. $\endgroup$
    – Abel
    Apr 3 at 12:06
  • $\begingroup$ You can't restrain a slender column against buckling by linking it to a similar column in the same state. In a simple example, the buckling strength of a ladder is just twice that of one of the uprights, despite the added bracing of the rungs. The reason is explained in 3rd year structures, basically the effective bending stiffness of a heavily loaded section is much lower than you'd expect. I can't remember the posh term for it. $\endgroup$ Apr 5 at 2:39
  • $\begingroup$ @GregLocock That's because the rungs only brace the uprights in one buckling direction. If you had a second ladder next to the first and added rungs between both you'd end up with a structure similar to those used in tower cranes. $\endgroup$
    – Zegpi
    May 7 at 13:37

1 Answer 1


It depends on the nature of connections with beams. I suggest you review a text in structural stability. Because depending on the end conditions, you get different effective lengths that govern the buckling equation which are obtained with differential equations that use end conditions as constraints. This is not so complicated, just the basics of a structural stability course really, so I suggest take a look at the first sections of a structural stability book. This effective length concept is also taught normally in a structural steel design class at undergrad level.


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