2.5-24 A rigid steel plate is supported by three posts of high-strength concrete each having an effective cross-sectional area A = 40,000 mm- 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 Gallow = 20 MPa. (Use E = 30 GPa for concrete.) S L PROBLEM 2.5-24