Stochastic Seismic Analysis of Structures with Nonlinear Viscous Dampers

Fluid damper devices inserted in buildings or bridges are commonly used as energy sinks for seismic protection. In the response analysis of structures with filled damper devices the main problem exists in the strong nonlinear behavior of such equipment, as a consequence the differential equation of motion remains nonlinear and the response spectrum analysis still cannot be applied. In this note, by using the concept of power spectral density function coherent with the elastic response spectrum and by using the statistical linearization technique, expressions for finding the equivalent linear damping have been found. Comparisons with results obtained by Monte Carlo simulations confirm that for the kind of nonlinearity induced by fluid dampers the statistical linearization technique gives satisfactory results in terms of second order moments, as well as in terms of absolute maximum peak response. The latter is evaluated by the semiempirical formulation of Vanmarcke.