The center rod CD of the assembly is heated from T 1 = 30°C to T 2 = 180°C using electrical resistance heating. At the lower temperature T 1 the gap between C and the rigid bar is 0.7 mm. Determine the force in rods AB and EF caused by the increase in temperature. Rods AB and EF are made of steel, and each has a cross-sectional area of 125 mm 2 . CD is made of aluminum and has a cross-sectional area of 375 mm 2 . E st = 200 GPa, E al = 70 GPa, and a al = 23(10 −6 )/°C.