A steel rod 20 mm diameter passes centrally through a copper tube of 25 mm internal diameter and 35 mm external diameter. Copper tube is 800 mm long and is closed by rigid washers of negligible thickness, which are fastened by nut threaded on the rod as shown in Fig. The nuts are tightened till the load on the assembly is 20 kN. Calculate the initial stresses in the copper tube and steel rod. Also calculate increase in the stresses, when one nut is tightened by one-quarter of a turn relative to the other. Take pitch of the thread as 1.6 mm. Take E for steel and copper as 200 GPa and 100 GPa respectively.