The center aluminum rod cd (ea = 70 gpa, αa = 23 × 10−6/°c) of the assembly is heated from 30°c to 180°c using electrical resistance heating and the temperature in the two identical steel rods ab and ef(es = 200 gpa, αs = 12 × 10−6/°c) rises from 30°c to 50°c. each steel rod has a cross sectional area of 125 mm2 and the cross sectional area of the aluminum rod is 375 mm2. if there is a 0.7-mm gap between rod cdand the rigid top block bf at 30°c, determine the normal stresses in the rods caused by the increase in temperature.