Robust stochastic design of viscous dampers for base isolation applications

Abstract eng:
Over the last decades, there has been a growing interest in the application of base isolation techniques to civil structures, in order to improve their earthquake resistant performance. Of the many relevant research topics, the efficient design of additional dampers, to operate in tandem with the isolation system, has emerged as one of the more important. One of the main challenges of such applications has been the explicit consideration of the nonlinear behavior of the isolators or the dampers in the design process. Another challenge has been the efficient control of the dynamic response under near-field ground motions. Such motions frequently include a strong longer-period pulse that has important implications for flexible structures, such as base-isolated systems. The current work proposes a framework that addresses both these challenges. A probability logic approach is adopted for addressing the uncertainties about the structural model as well as the variability of future excitations. This is established by characterizing the relative plausibility of different properties of the system and future excitations by probability models. In this stochastic setting, a realistic model for the description of near-field ground motions is discussed. This model establishes a direct link, in a probabilistic sense, between our knowledge about the characteristics of the seismic hazard in the structural site and future ground motions. The design objective is then defined as the maximization of structural reliability, quantified as the probability that the structural response will not exceed acceptable performance bounds. A simulation-based approach is implemented for evaluation of the stochastic performance of the base isolated structure. An efficient framework is discussed for performing the associated challenging design optimization and for selecting values of the controllable damper parameters (corresponding to the design variables) that optimize the system reliability. The methodology is illustrated through application to a base isolated building with lead-rubber bearings and additional nonlinear passive viscous dampers. Uncertainty is included in both the structural model as well as to the model for the near-fault excitation. The effect of the maximum forcing capability of the dampers on the system performance is also investigated. The results demonstrate the efficiency of the proposed methodology and the importance of a simulation-based design framework that can address all important system nonlinearities.

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