The object of this paper is to report an experimental investigation on the internal force distribution in reinforced concrete (RC) frames with added RC walls. The paper describes a special test setup and force transducers designed to determine the internal forces. The transducers were designed so that the stiffness change in the column would be minimal. The paper reports the results of a test in which a 1/3-scale, two-story, three-bay RC frame was first subjected to damaging lateral-drift reversals and was then strengthened with the addition of an RC wall to fill the middle bay and subjected again to drift reversals. The frame, built purposely with the deficiencies commonly observed in buildings in Turkey, was displaced to a roof-drift ratio of 1.6%. The frame developed a base shear force of approximately 14 kN. Two RC walls were then cast to fill the middle bay. Tested in that condition to a drift of 1.6%, the modified structure developed a base shear force of approximately 53 W. The observed hysteresis loops were stable even though slip of the longitudinal bars was observed at the splices in the interior columns.