A scaled prototype of an MR damper was active in passive mode on a 160 ton tuned mass in a 21-story building in Santiago, Chile, during the February 27, 2010 earthquake. More recently, a full scale ±100 cm stroke MR damper was designed, manufactured, and is being tested for the same building. The implementation considers a new real time structural measurement system developed to acquire building displacements as feedback for the physical controller of the TM-MR damper assembly. The new measurement system was successfully tested on a shaking table model at Empa. Moreover, results from a number of nonlinear simulations on the building with the full scale semi-active damper shows that the mean displacement reduction for the setup considered is 22% more effective than the building with the bare tuned masses. Finally, the solution was identified to be fairly cost-effective as compared with a passive solution or the bare case.