## 7 Conclusions  
A practical design was proposed for a seismic protection system that is suitable for slender metallic frames and that is based on dissipative bracings that integrate MRD dampers. The nonlinear relationship between the dissipative force and the piston speed of the MRD was replaced by a linear equation that involves the evaluation of an equivalent damping coefficient for the MRD. A rational method was adopted for the calculation of the equivalent damping coefficient by assimilating the MRD to a proportional damper that dissipated the same amount of energy during the seismic event. The linearization of the dynamic behavior of the magnetorheological fluid dampers allowed for the implementation of a robust iterative process for the evaluation of the seismic response of the structure in correspondence with the different activation levels of the embedded MRDs. The response was first evaluated in the generalized coordinates domain, and then in terms of the acceleration and speed of the structural nodes with respect to the base of the structure. A current intensity of 0.5 A was found to be adequate to achieve the target 50% reduction in the acceleration-response peaks at each floor. A true-scale model of the reference structure was then manufactured and installed on a shaking table, which provided the reference seismic excitation. The acceleration response was measured at each floor of the structure in three operative conditions: (1) A clean structure (no dissipative bracings installed); (2) With the vibration-suppression system off (dissipative bracings installed and MRD not activated); (3) With the vibration-suppression system on (dissipative bracings installed and MRD activated by a current of 0.5 A). With respect to the \"clean structure\" case, the activation of the MRD led to an average reduction of nearly 70% for the peaks of the floor accelerations with respect to the base of the structure, as well as for the interstory accelerations. The higher level of abatement with respect to the design target can be justified by considering the intrinsic limitations of the numerical simulations that did not take into account the extra damping that was due to the friction between the structural elements at their interface joints. A slight increase in the modal damping of the clean structure with respect to the assumed value (1.5% for all modes) would have surely limited the discrepancy between the numerical expectations and the experimental outcomes. On the other hand, the proposed simulation strategy is mainly intended to provide a fast and practical tool for the robust design of the seismic mitigation system; in light of this consideration, any simplification is acceptable if it results in the safer design of the system. The robustness and effectiveness of the conceived system are further proven by the recorded seismic response of the structure in the case of MRDs being installed and inactivated. The average reduction factor for the floor acceleration peaks and for the interstory acceleration peaks is nearly 48%, even if some floors have a reduction factor lower than 50%. This means that, even in the case of a blackout (highly probable during an earthquake) or the malfunction of the hardware that powers the MRDs, the system still maintains good abilities to dampen the structural response to the seismic excitation. The achievement of significant vibration-suppression levels in the case of both activated and nonactivated devices represents a remarkable result, which shows not only the effectiveness of MRDs, but also the soundness of the design and simulation approaches that were adopted for the assessment of the seismic protection system's dynamics. Part of the research described in this paper has been carried out within the framework of the Tellus Stability Project, which was funded by the Italian Ministry of Research, Instruction and University, in the framework of the FAR platform, and pursuant to Article 5 of Ministerial Decree No. 593/2000. Not applicable.