고체역학 (Beer) — Pure Bending: Problem 4.54

4.54 For the concrete beam shown, the modulus of elasticity is 25 GPa for the concrete and 200 GPa for the steel. Knowing that \( b = 200 \text{ mm} \) and \( d = 450 \text{ mm} \), and using an allowable stress of 12.5 MPa for the concrete and 140 MPa for the steel, determine (a) the required area \( A_s \) of the steel reinforcement if the beam is to be balanced, (b) the largest allowable bending moment. (See Prob. 4.53 for definition of a balanced beam.)