This paper analyzes the application of semi-active variable damping TMD (SAVDTMD) with piezoelectric friction dampers as an alternative to existing methods to control floor vibrations, especially walking-induced vibrations. The use of a MDOF floor model in the analysis provides some insight on the effect of modes not targeted in the design of the controller. An optimal semi-active control law originally developed for vehicle suspension control was incorporated into the analytical models. Two floor system examples, typical of those that would have a floor vibration problem, are evaluated and shown to be controlled successfully by the SAVDTMD at both the targeted and untargeted modes. Problems of spillover of the control force to untargeted modes was analyzed and determined to be stabilizing.