AT$1.$ Three vertical rods $AB,CD,EF$ are hung from rigid

supports and connected at their ends by a rigid horizontal bar.

The rigid bar carries a vertical load of $20kN.$ Details of the bars

are as follows:

Bar $AB$ :$-L=500mm,A=100m{m}^2,E=200$GPa

Bar CD:$-$ L$=900$ mm$,A=300m{m}^2,E=100$GPa

Bar EF:$-L=600mm,A=200m{m}^2,E=200$GPa

If the rigid bar remains horizontal even after loading,

determine the stress and elongation in each bar.