Seismic protection and retrofitting through nonlinear fluid viscous damper interconnecting substructures

"The use of passive control devices to improve seismic performance by interconnecting adjacent structures is not completely exploited in real applications, due to the lack of simple design procedures. The paper analyzes the beneficial effects of such a dissipative coupling in a simple 2dofs model, subjected to ground motion, aiming to define the main problem features. In this respect, a unified approach may be utilized at the preliminary design stage to analyze the performance of passive devices, described either by the Kelvin-Voigt or the Maxwell model. The main mechanical parameter values are assessed on the base of the different sensitivity of the system spectral properties to wide-range variations of the stiffness and viscosity parameters describing the coupling device. In both parallel and series layouts, it is shown that a peculiar point in the parameter space is characterized by a pair of coincident complex eigenvalues. A discussion on the properties of the associated system is presented, evidencing through numerical analyses the occurrence of optimal performances in terms of response reduction. Different types of synchronous ground motion, including white-noise and real earthquake time histories (El Centro 1940, Kobe 1995, L’Aquila 2009) are used to validate the procedure. Starting from this optimal condition, small nonlinearities in the viscous law are introduced, in order to characterize the achievable enhancement in the system performance. "