Fundamental considerations for the design of non-linear viscous dampers

Two interrelated issues related to the design of non-linear viscous dampers are considered in this paper: structural velocities and equivalent viscous damping. As the effectiveness of non-linear viscous dampers is highly depe ndent on operating velocities, it is important to have reliable estimates o f the true velocity in the device. This should be based on the actual relat ive structural velocity and not the commonly misused spectral pseudo-veloci ty. This is because if spectral pseudo-velocities (PSV) are used, they are based on design displacements (S-v = omega(o)S(d)) and are thus fundamental ly different from the actual relative structural velocity. This paper exami nes the difference between these two velocities, and based on an extensive study of historical earthquake motions proposes empirical relations that pe rmit the designer to transform the well-known spectral pseudo-velocity to a n actual relative structural velocity for use in design. Non-linear static analysis procedures recommended in current guidelines for the design of str uctural systems with supplement damping devices are based on converting rat e-dependent device properties into equivalent viscous damping properties ba sed on an equivalent energy consumption approach. Owing to the non-linear v elocity dependence of supplemental devices, an alternative approach for con verting energy dissipation into equivalent viscous damping is advanced in t his paper that is based upon power consumption considerations. The concept of a normalized damper capacity (epsilon) is then introduced and a simple d esign procedure which incorporates power equivalent linear damping based on actual structural velocities is presented. Copyright (C) 1999 John Wiley & Sons, Ltd.