The Effect of Nonlinear Response of the Primary System in Nonconventional TMDs

Tuned Mass Dampers (TMD) have been widely used in the passive vibration control of engineering structures, both under wind and seismic loads. Under wind loads, a proper frequency tuning ensures a significant response reduction of the primary structure. While under wind loads the structure is likely to remain in the elastic range of behaviour, when large earthquakes occur it can experience inelastic deformations and damage, with a consequent de-tuning effect. In this paper, nonconventional TMDs with large mass ratios, realized through Interstory Isolation Systems (IIS), are considered and the influence of the inelastic behaviour of the primary system on the overall structure response is analysed. In detail, IIS is employed for retrofitting existing masonry buildings through a vertical extension, isolated at its base and built up on the roof of the existing structure. Pivot-type hysteretic models are used to grasp the mechanical behaviour of the masonry structure. Based on a case-study building, time history analyses on 3D Finite Element models are implemented. The results of nonlinear time history analyses show that in the building with the vertical extension both displacements and hysteretic energy dissipated by the masonry piers, are lower than in the as-is building, confirming that, although a de-tuning effect can occur, the inelastic engagement of the original structure is significantly reduced.