Eccentrically Loaded Struts — Choice of Section For compression members subjected to eccentric axial load, which type of cross-section is generally preferred and why?

Introduction:
Eccentric compression introduces combined axial stress and bending. The selection of cross-section must therefore consider section modulus, radius of gyration, and material economy to limit maximum compressive stress and reduce buckling risk.

Given Data / Assumptions:

• Member: slender strut/column under axial load with eccentricity e.
• Material: isotropic, linear elastic.
• Design aims: high stiffness and strength per unit weight, improved stability (larger radius of gyration) and better distribution away from the neutral axis.

Concept / Approach:
For the same area, hollow (tubular) sections place more material away from the centroid, increasing both section modulus and radius of gyration k. This reduces bending stress sigma_b = M / Z and increases Euler capacity P_cr proportional to (E * I) / (L_e^2) since I = A * k^2 grows with k when area is away from the center.

Step-by-Step Solution:
Model combined stress: sigma_max = P / A + M / Z with M = P * e.For given A and e, larger Z reduces M / Z hence lowers peak stress.Hollow sections maximize Z and k for a given mass by shifting material outward.Buckling capacity improves since I = A * k^2 increases with k.

Verification / Alternative check:
Compare a solid round bar and a tube with the same mass: the tube shows higher I and Z, confirmed by standard section property tables.

Why Other Options Are Wrong:
solid section: concentrates material near the center, giving smaller Z and k for the same weight.composite section: may be useful but the generic preference for eccentric loading is a hollow section due to efficiency.reinforced section: vague; does not specify geometry that improves Z and k.

Common Pitfalls:
Ignoring eccentricity in stress checks and relying only on P / A.Forgetting the role of effective length and end conditions on buckling capacity.

Final Answer:
hollow section