Two parallel walls 6 m apart are stayed together by a steel rod 20 mm diameter passing through metal plates and nuts at each end. The nuts are tightened when the rod is at a temperature of 100°C. Determine the stress in the rod when the temperature falls down to 20°C if
1. The ends do not yield.
2. The ends yield by 1mm.
Take E = 2.0 × 10⁵ N/mm² α = 12 × 10⁻⁶ /°C.