In previous studies several models have been formulated for the simulation of the dynamic response of hybrid base-isolation systems, that is coupled High Damping Rubber Bearings (HDRB) and Low Friction Sliding Bearings (LFSB). The HDRB component has been modelled by a bilinear spring while two different models have been used for the LFSB component. In one formulation the Constant Coulomb Friction Model (CCFM) has been used while in another the Linear Coulomb Friction Model (LCFM) has replaced the previous model. In both cases a linear viscous damper is used as an additional source of energy dissipation. By combining the models of the various components several models for the coupled system can be obtained.

For the case of free vibrations due to the sudden release of forces, imposed by applying an initial displacement to the system, an analytical solution has been provided for the resulting motion, Oliveto et al. (2010), Athanasiou and Oliveto (2011). The solution provided describes the complete picture of the dynamic behaviour of the hybrid base-isolation system under free-vibration, that is displacement, velocity and acceleration time histories, force-displacement relationships for each system component, energy balance for the whole system and individual contributions to energy dissipation.

The potential of the models for dynamical structural identification of base-isolation systems has been demonstrated, Oliveto et al. (2010), Athanasiou and Oliveto (2011). Currently the scope of the identification potential of the models is being investigated through interdisciplinary studies involving evolution strategies. Those results are going to be presented in the Genetic and Evolutionary Computation Conference (GECCO 2011). Experimental records from tests on a building in the town of Solarino, seismically retrofitted by hybrid base-isolation, have been and are being used for the identification of the base-isolation system. The results should allow not only to evaluate the performance of the optimization strategies used but also to assess the robustness and reliability of the mechanical models considered.

The object of the present work is to extend the previous formulations to the evaluation of the response of hybrid base-isolation systems to earthquake ground motions. This will require the development of a numerical algorithm for the incremental response history based on variation methods already being used by members of the research team. It is expected that the new formulation will enable the simulation of the earthquake response of hybrid base-isolation systems. Also the numerical solutions obtained should allow for the dynamic identification of the isolation systems directly from earthquake response records.

References:

Oliveto, N.D., Scalia, G. and Oliveto., G. (2010). "Time domain identification of hybrid base isolation systems using free vibration tests," Earthquake engineering and structural dynamics, 39(9):1015-1038.

Oliveto, G. and Athanasiou, A. (2011). "Modelling Hybrid Base Isolation Systems For Free Vibration Simulations," 8^th International Conference on Urban Earthquake Engineering, Tokyo, Japan.