A rectаngulаr beаm has a crоss sectiоn оf b = 16 in., h = 26 in., and d = 23.5 in. It is reinforced with three No. 6 Grade 60 bars. The concrete strength is 2,500 psi (normal weight). The beam has Grade 60 No. 3 stirrups. Determine the assumed modulus of elasticity of the concrete, Ec.