18. The stepped bar shown in the figure is subjected to a force at the center. Use FEM to determine the displacement field u(x), axial force distribution P(x), and reactions and Rr.

Assume E = 100 GPa areas of cross-sections of the three portions shown are, respectively.

10~4, 2 x 10~4 and 10~4 m2, andF = 10,000N.

< 0.3 m |( 0.4 m > L 0.3 m y

* Rr