On the probabilistic seismic assessment of structures with added viscous dampers

The purpose of this paper is to propose a simplified probabilistic procedure for the seismic assessment of nonlinear structures equipped with nonlinear fluid viscous dampers. The considered reference probabilistic approach is the 2000 SAC-FEMA method, which allows to obtain the probability of exceeding a specified performance level. Within this method, in general, the probabilistic seismic demand analysis is performed in terms of incremental dynamic analysis (IDA) by considering several earthquake records. This approach has been followed with reference to a set of case studies, characterized by RC frames with and without added dampers. The main characteristics of the proposed simplified approach are: the application of a direct procedure previously proposed by the authors for the response assessment of structures with dampers as an alternative to nonlinear incremental dynamic analyses; the study of the relation between the dispersion of seismic demand of structures with dampers with that of structures without dampers. The latter, in fact, can be estimated also on the basis of several available literature data. In this paper the direct procedure previously proposed by the authors has been applied to the case studies for increasing values of seismic intensity. The results of such applications have been then compared with those of the IDA analyses in terms of the relation between the roof displacement demand and the seismic intensity. The results of the IDA analyses have been also examined in order to determine the correlation between the dispersion of demand of structures with dampers with that of structures without dampers. Finally the values of probability obtained with the proposed simplified approach has been compared with those of the 2000 SAC-FEMA method based on IDA analyses.