Increasing which geometric property of a pipe increases elastic buckling resistance?

• A. Decreased diameter
• B. Increased diameter
• C. Reduced material strength
• D. Increased wall thickness

Answer: (D)

Elastic buckling resistance comes from cross‑section stiffness, quantified by the moment of inertia. For a hollow pipe, thickening the wall while keeping the same outer diameter increases the area of material farther from the centroid, which raises the moment of inertia I (I ≈ π/64 (Do^4 − Di^4)). Since the elastic buckling load scales with I as P_cr = π^2 E I / (K L)^2, a larger I means a higher load the member can sustain before buckling. Reducing the diameter would generally lower I and weaken buckling resistance; reducing material strength doesn't increase the structural stiffness; increasing diameter could raise I, but thickening the wall directly boosts cross‑sectional stiffness for a given outer size, making it the most effective way to increase elastic buckling resistance.