Two-story, three-bay reinforced concrete (RC) frames with and without internal steel frame (ISF) retrofits were tested using continuous pseudo dynamic test method. The ISFs were installed to the middle bay of the RC frame. Test results indicated that ISF retrofit was beneficial in resisting deformation demands without significant damage under simulated ground motions. The ISF shifted the failure mode of the system from a brittle to a ductile mode. The test results were compared with the results of the nonlinear time history analysis. The analysis results were capable of tracing the overall behavior of global response parameters; however, estimations of local demand parameters were less accurate. Copyright (c) 2012 John Wiley & Sons, Ltd.