Vertical seismic protection of structures with inerter-based negative stiffness absorbers

One of the most effective approaches for seismic protection of structural systems is isolation. The majority of existing seismic protection systems are related to horizontal ground motion and only few focus on vertical seismic components, as this would require vertical flexibility, a feature conflicting with the need for sufficient support of the isolated structure. In order to overcome this difficulty, a novel vertical Stiff dynamic absorber (SDA) is proposed that combines a Quasi-Zero Stiffness design including negative stiffness elements, an enhanced Tuned Mass Damper, and Inerter elements. The present work deals with the optimization problem for the determination of the various design parameters of the proposed configuration, aiming at minimizing the vertical accelerations induced on the structure while keeping the displacement within reasonable limits. The values of the optimized design parameters depend only on the characteristics of the isolated structure irrespectively of the excitation input. This feature differentiates the proposed SDA from similar versions found in the literature and renders the design applicable for use across a wide range of vertical vibration control applications. The proposed configuration is designed to achieve great acceleration isolation without compromising the weight-bearing capacity of the structure. This is realized through the appropriate determination of the static and dynamic stiffnesses via a novel calculation approach that is based on the initial static equilibrium point. The role of various design factors is investigated based on time-history responses of a reference structure to artificial accelerograms matching EC8 criteria, and the effect of the optimized SDA is evaluated on real earthquake records, confirming its capacity to greatly reduce the response to structure accelerations. The selection of the design parameters is based on engineering criteria and an indicative implementation of the design elements is included, demonstrating the feasibility of the proposed configuration.