A rigid steel plate is supported by three posts of high-strength concrete each having an effective cross-sectional area A=40,000 mm^2 and Length L=2 m (see attachment). 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 equal to 20 MPa.(Use E=30 GPa for concrete)
THE ANSWER SHOULD BE 1.8 MN