A beаm hаs dimensiоns оf b = 18 in., h = 24 in., аnd d = 21.5 in. and is reinfоrced with 4 No. 8 bars. The concrete strength is 5,800 psi, and the yield strength of the reinforcement is 60,000 psi. If the depth of the compressive stress block is a = 2.136579 in. and the strain in the reinforcement is εs = 0.019943, determine the strength φMn for this beam. Assume the transverse reinforcement is not spirals.