A direct design procedure for frame structures with added viscous dampers for the mitigation of earthquake-induced vibrations

A direct procedure for the seismic design of building structures with added viscous dampers is described in this paper. The procedure is applicable to regular multi-storey frame structures which are characterized by a period of vibration lower than 1.5 s. It aims at providing practical tools for the direct identification of the mechanical characteristics of the manufactured viscous dampers as well as for the structural design of the frame members' so that a target level of performance is achieved. The design philosophy is to limit the structural damages under severe earthquakes. First, a target damping reduction factor is selected to achieve the desired reduction in the peak structural response. The linear damping coefficients of the equivalent linear viscous dampers are calculated taking advantage of modal damping ratios properties of classically damped systems. Then, simple analytical formulas for the estimation of peak inter-storey velocities are used, together with an energy criterion to identify the non-linear mechanical characteristics of the manufactured viscous dampers. Finally, the internal actions in the structural elements are estimated through the envelope of two equivalent static analyses (ESA), namely: ESA1 in which the naked structure is subjected to a first set of equivalent lateral forces, and ESA2 in which the structure, with rigid diagonal braces substituting the added viscous dampers, is subjected to a second set of equivalent lateral forces. At this preliminary stage of the research, the procedure is targeted for the preliminary design phase, since correction factors to improve the accuracy in the estimation of the peak inter-storey velocities needs to be calibrate. Therefore, for final design, non-linear dynamic analyses are recommended.