Deflection of a Perfect Strut Under Point Forces

[dichotomy]

hello all, first post here so don't bite.

if a perfect strut was compressed by an 2 imaginary point forces acting exactly on its centroid, and ignoring outside effects, would it bend laterally, and why so? when I say perfect, i mean ignore all consequences of practicality, ie. the alignment is precise to the eg. atom, and the bar is of impeccable geometry along its length.

i was having a debate about this for at least 20 minutes with someone, and I saw no good reason why it should (ignoring material failure for the moment), since the point forces acting on the centroid produce no moment/horizontal component to cause the strut to bend in such a dramatic manner.

 

[Pyrrhus]

What? Be more clear. If one of the components of a load is perpendicular to the centroidal axis (beam, bar, slab, etc...), then there would be bending!.

 

[FredGarvin]

In your perfect example, I guess there is no real reason for the column to buckle. You would then have to deal with compressive failure. If there is no moment at the ends or eccentricity to the load and the material is perfectly homogeneous, it should be in perfect compression. I had to take a quick look back in one of my books to make sure the Euler equation for buckling is derived assuming that there is an applied moment at the end of the column.

 

[chief]

hello all, first post here so don't bite.

if a perfect strut was compressed by an 2 imaginary point forces acting exactly on its centroid, and ignoring outside effects, would it bend laterally, and why so? when I say perfect, i mean ignore all consequences of practicality, ie. the alignment is precise to the eg. atom, and the bar is of impeccable geometry along its length.

i was having a debate about this for at least 20 minutes with someone, and I saw no good reason why it should (ignoring material failure for the moment), since the point forces acting on the centroid produce no moment/horizontal component to cause the strut to bend in such a dramatic manner.

You have to know several different things before you can answer that question.

1) end restraints (it is common to assume that both ends are pinned or free to rotate)
2) moment of inertia of the section (about both axes)
3) unbraced length of the strut in compression
4) the amount of load applied

As the strut length gets longer, the section gets smaller, or the applied load gets larger, the strut will be more likely to buckle and deflect laterally. Assuming the section is sized appropriately, it will not buckle and will not deflect lateraly.