Stochastic optimum design criterion for linear damper devices for seismic protection of buildings

This paper concerns a new approach for the reliability-based optimum design of linear multistory frames seismically protected by viscous dampers. A deterministic objective function, defined as the total added damping, is minimized, while stochastic restraints impose a limit to system failure probability. This latter is here related to a maximum interstory drift crossing over a given value, which is associated with damage control requirements. System failure probability is evaluated by means of the covariance analysis of a frame subject to a seismic load represented by a nonstationary modulated Kanai-Tajimi stochastic process. Numerical examples are developed, concerning a plane-shear-type frame with three floors equipped with viscous damper devices. Two different possible design solutions are performed, considering different earthquake intensities: more in detail, the first adds constant damping at each story, while the second considers a variable added damping distribution.