A multi-objective design procedure for the seismic retrofit of framed structures with fluid viscous dampers

The 2025 Global Assessment Report on Disaster Risk Reduction highlights the persistent societal and economic burden of disasters and warns that post-disaster reconstruction too often restores pre-existing conditions rather than systematically incorporating risk-reduction measures. This reinforces the need for preventive seismic upgrading, particularly in Europe, where much of the building stock was constructed before modern seismic design standards. The European challenge is twofold: dedicated provisions for buildings equipped with energy-dissipation systems were introduced only in the second generation of Eurocode 8, leaving their practical implementation dependent on engineering judgement and iterative design; meanwhile, several methodologies proposed in the literature typically address a single structural performance target at one seismic limit state. Yet earthquakes of different intensities can cause distinct structural and non-structural damage, with economic losses and functional disruption even when structural safety is preserved. This paper presents the first formulation and numerical validation of a multi-objective methodology for designing fluid viscous damper (FVD) systems in existing framed buildings. The procedure simultaneously considers displacement-based performance targets at different limit states, reflecting different performance requirements and supporting risk-informed retrofit decisions. These targets are used to determine the damper properties through constrained optimization and their subsequent distribution along the building height. In this formulation, FVDs are idealized as purely viscous dissipators, neglecting the elastic deformability of the damper–brace assembly. The proposed methodology thus represents a step toward integrating multi-level seismic performance requirements into practical retrofit design, supporting the development of more proactive strategies for reducing the vulnerability of existing buildings.