Question

compare the suitability of the solid rectangular and hollow square columns to support a compressive load and comment on two of their key geometrical design aspects.

Answer 1

The hollow square column can withstand the same stress as that of solid rectangular column...
Strength to weight ratio is better for a hollow square than a solid rectangular column. This means a hollow square column is stronger than a solid rectangular column of equal mass and the same material.

The maximum shear stress is at the outer side of surface, so the elements at the outer side is contributing its full resistance force to torque applied while the inside elements are not contributing its full resistance, thus causing loss of material.

For resisting the torsion load the polar moment area is considered as the resisting area so, if polar moment area of any shape is more it can withstand more torque compared to other.