(Answer is buckling), following up, how and where would you reinforce the member? What would be the best cross section to resist buckling?
Buckling is dominant failure mode. Reinforced with sleeve on the middle of the member. Not sure best cross section
I’m heavily referencing this article linked here, so I’ll be summarizing the key points from the article
One way to think about buckling is that it’s a force applied to the neutral axis of a beam. Instead of applying it like you would in bending a beam (i.e. compressive force), it’s along the length of the beam member.
The buckling force, P, is directly proportional to the stiffness of the beam, C. The constant C can be calculate as E*I, where E is the modulus of elasticity and I is the moment of inertia of the cross-section. The cross-section here is directly tied to the variable I, so the cross-sections that yield the highest I value would be the best cross-section to use.
Quoted from the post above.
In general, buckling can be prevented by using a larger cross-section or stiffer material. Whatever can be done to increase the stiffness of the cross-section, E*I will help. Additionally, it can be seen in the critical load calculation that the buckling load is inversely proportional to the length of the structural member squared, so if required, reducing the length of the structural member or bracing the member can be used to increase the critical buckling load.
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