Which failure mode is associated with slender columns under axial compressive load?

• A. Buckling
• B. Compressive failure
• C. Tension
• D. Shear

Answer: (A)

Buckling is the failure mode for slender columns under axial compression. When a column is slender, it tends to become unstable and bend laterally as the compressive load increases, so it loses its ability to carry load even before the material yields. This instability, known as Euler buckling, depends on stiffness and geometry: the critical load Pcr = π^2 E I /(K L)^2 shows that increasing length or reducing stiffness (I or E) lowers the load at which buckling occurs. In short, slender columns fail by lateral deflection due to instability rather than by crushing of the material itself; short, stocky columns may fail by compressive crushing instead, and tension or shear are not the primary modes under pure axial load.