Design and Retrofit Methodology for Building Structures with Supplemental Energy Dissipating Systems

This report considers two issues related to the design of nonlinear viscous dampers: structural velocities and equivalent viscous damping. As the effectiveness of non-linear viscous dampers is highly dependent on operating velocities, it is important to have reliable estimates of the true velocity in the device. This estimate should be based on the actual relative structural velocity and not the commonly misused spectral velocity. This is because spectral velocities are based on design displacements (Sv=mo Sd) and are thus fundamentally different from the actual relative structural velocity. The difference between these two velocities is examined, and based on an extensive study of historical earthquake motions, empirical relations that permit the designer to transform the well-known spectral velocity to an actual relative structural velocity for use in design are proposed. Nonlinear static analysis procedures recommended in current guidelines for the design of structural systems with supplemental damping devices are based on converting rate-dependent device properties into equivalent viscous damping properties based on an equivalent energy consumption approach. Due to the nonlinear velocity dependence of supplemental devices, an alternative approach for converting energy dissipation into equivalent viscous damping is advanced paper that is based upon power consumption considerations. The concept of a normalized damper capacity (E) is introduced and a simple design procedure which incorporates power equivalent linear damping based on actual structural velocities is presented. Based on these studies, general step-by-step retrofit/design algorithms are presented for building structures with supplemental damping systems. An overall strategy is presented for the various phases of the design process. This includes facets of conceptual and preliminary design as well as the final design verification process. The efficacy of the preliminary design phase is improved by a well-conceived SDOF idealization of the structural system. This is followed by a brief overview of performance objectives. The general normalized design parameters for the supplemental system are then transformed for the MDOF system based on the specific configuration details. Finally, the design of a nine-story building is presented as an example of the applicability of proposed design algorithms and alternative system configurations.