Derive, from first principles, an expression for the compressive buckling load on a simply supported beam of length l and flexural rigidity, EI. State the assumptions used. A simply supported straight steel beam 2.5 m long and of 20 mm by 10 mm rectangular cross-section is loaded axially in compression until it buckles. Calculate the maximum deflection of the beam before the material attains its yield stress of 350 MN/m2