In a historic construction, a beam should be supported with a rod as a compression member The 3mlong member will be pin supported at each end Either hollow square rod or hollow circular rod will be used The inner and outer diameters of the hollow circular rod are 4cm and 6cm, respectively The outer width ( depth) of the hollow square rod is 6cm 

Find the wall thickness of the hollow square rod so that rods have the same cross-sectional area (so that the same amount of material is used) 

Based on the critical load for each rod, decide on which rod to use as a compression member in this historic construction Youngs modulus of the rod material is 105000 MPa.