Tuned mass damper and base isolation: A unitary approach for the seismic protection of conventional frame structures

Taking inspiration from the basic two-degree-of-freedom (2-DOF) models usually adopted to study base isolation (BI) and tuned mass damper (TMD), a unique main archetype 2-DOF model is here introduced to describe the behavior of general multi-degree-of-freedom (MDOF) frame systems, in which a stiffness discontinuity (disconnection), such as the one that can be identified in BI or TMD, may be inserted. With the aim to evaluate the dynamic enhancement following from such a discontinuity for the two masses of the model, two reference schemes (TMD scheme and BI scheme) are introduced and two particular mean gain parameters are associated with them. These represent the main subject of the parametric analyses presented in this work, based on variable mass and stiffness ratios. These analyses are carried out considering groups of earthquake records collected on the basis of a specific criterion (spectrum compatibility). The results of the parametric analyses are arranged by means of mean gain maps and surfaces that can be directly related to a reference response spectrum. The mean gain maps provide a description of the dynamic performance of the archetype model. In order to extend the results obtained for the archetype models to general MDOF frame systems, a specific equivalence procedure is then introduced. Using such an approach, it is possible to define values of mass and stiffness ratio for a general MDOF systems, and then to use the maps to design the characteristics of the disconnection. The results expressed by the mean gain maps have been confirmed by several simulations carried out with reference to a 6-story shear-type frame, thus showing some practical implications of the research.