90 kN 400 mm B Rigid beam AB rests on the two short posts shown in Fig. 4-7a. AC is made of steel and has a diameter of 20 mm, and BD is made of aluminum and has a diameter of 40 mm. Determine the displacement A of point F on AB if a vertical load of 90 kN is applied over this point. Take Ext = 200 GPa, El = 70 GPa. SOLUTION Internal Force. The compressive forces acting at the top of each post are determined from the equilibrium of member AB, Fig. 4-7b. These forces are equal to the internal forces in each post, Fig. 4-7c. 90 kN 200 mm 200 mm 400 mm 300 mm D (a) 60 kN 30 kN (b) 0.102 mm -600 mm A F- 400 mm- B 60 kN 30 kN 0.102 mm бр 0.184 mm (d) 0.286 mm PAC 60 kN Pap-30 kN