Question

Determine the ratio of strenghts of a solid steel column to that a hollow column of the same material and having the same cross sectional area. The internal diameter of the hollow column is 1/2 of its external diameter. Both the columns are same length and are pinned at their both ends

Answer 1

Hints:
Axial stress is the same because the same load is distributed over the same area.
However, buckling strength is widely different.

Calculate the ratio of the area moments of inertia, and compare buckling their strengths using Euler's buckling formula:
F=π²2EI/(KL)²
where E,I are Young's modulus, I=area moment of inertia, K=end condition constant, equals 1 when pinned, and L=length of columns.

See also for more explanation on buckling:
http://en.wikipedia.org/wiki/Buckling
or other textbooks on strength of materials.