Multi-objective optimization of buildings equipped with two-layer isolation systems with inerters

In recent decades, isolation systems have proven their value in reducing the structural response
(i.e., floor accelerations and interstory drifts) of buildings subjected to seismic loads. However, reduction of the structural response is achieved at the expense of large lateral deformations of the isolators. Naturally, it is then desirable to optimize the properties of the isolation system to simultaneously reduce both the lateral response and the lateral deformation of the isolators, but such optimization is not possible in traditional (i.e., one-layer) isolation systems because minimization of the lateral response and minimization of the lateral deformation of the isolators are competing objectives (i.e., when the structural response is minimized the lateral deformation
of the isolators is actually maximized, and vice versa). This study evaluates the possible implementation of two-layer isolation systems to simultaneously minimize both the structural response and the lateral deformation of the isolators. Further, possible addition of inerter devices is also examined. A multi-objective formulation is proposed to optimize the properties of linear two-layer isolation systems. The design variables are the stiffness, damping and inertance properties of each layer. The Nondominated Sorting Genetic Algorithm II (NSGA-II) is adopted to solve the multi-objective optimization problem. A 10-story shear building model is used to test the proposed methodology. The building model is subjected to the FEMA P-695 far-field record set. A minimum value criterion is proposed as high–order information on the Pareto front. Results are compared with those obtained from the analysis of optimized single-layer isolation systems and with those obtained from the analysis of optimized two-layer isolation systems without inerters.