A rigid steel plate is supported by three posts of high-strength concrete each having an effective cross-sectional area A 40,000 mm2 and length L 2 m (see figure). Before the load P is applied, the middle post is shorter than the others by an amount s 1.0 mm. Determine the maximum allowable load Pallow if the allowable compressive stress in the concrete is sallow 20 MPa. (Use E 30 GPa for concrete.)

 A rigid steel plate is supported by three posts of
high-strength concrete each having an effective cross-sectional area A 40,000 mm2 and length L 2 m (see figure). Before the load
P is applied, the middle post is shorter than the others by an amounts 1.0 mm.
Determine the maximum allowable load Pallow if the allowable
compressive stress in the concrete is sallow 20 MPa.
(Use E 30 GPa for concrete.)