Optimization of nonlinear fluid viscous dampers for building structures: Energy-based design approach under stochastic seismic excitation

It is well known that there are certain advantages in using nonlinear (rather than linear) fluid viscous dampers, primarily, the achievement of a desired seismic performance with reduced damper forces in comparison with linear counterparts. However, the excitation-dependent constitutive behavior of such nonlinear devices may complicate the related optimal design procedure so that, generally, multiple-step approaches are pursued by exploiting the concept of “energy equivalent” dampers after a preliminary optimization of linear viscous dampers is carried out. As an alternative, this contribution presents a stochastic-based numerical procedure in which the nonlinear behavior of the dampers is fully integrated in a single-step optimization process. In particular, a non-Gaussian stochastic linearization technique is used in the optimal design procedure to linearize the equations of motion of structures equipped with NFVDs and subject to a Kanai-Tajimi filtered random excitation. The optimal dampers are identified by addressing an energy-based objective function representing the energy dissipated by the devices out of the total input energy from the earthquake excitation. Therefore, the procedures aims to maximize the energy dissipation performance of the devices subject to a given constraint condition, namely a (desired) target added damping ratio. The effectiveness of the proposed energy-based stochastic design approach is assessed by comparison with alternative procedures through stochastic dynamic analysis as well as by performing nonlinear response history analysis under a suite of ground motion records.