Fluid viscous dampers (FVDs) are effective tools for improving building seismic performance, which can be applied to both new designs and retrofitting of existing structures. They absorb and dissipate seismic energy to minimize structural damage without increasing stiffness or natural period. The paper reviews the assessment and retrofitting of a 15-story building using an FVD system under Performance-Based Seismic Retrofitting (PBSR) criteria. It compares the FVD method to a primary model and contrasts it with traditional steel outrigger stiff­ ening systems. The findings show that FVDs significantly enhance seismic performance even with a small number of dampers, helping to minimize costs. This positive effect can be further amplified by selecting the optimal damper locations within the structure. Conversely, the steel outrigger system requires numerous structural members across all stories, leading to extended construction times and increased disruption to building occu­ pancy. Both FVD and outrigger systems improve drift, but their effects differ based on their arrangement and position. FVD can reduce maximum strain by up to 58.54 %, while steel outriggers reduce it to 73.375 %. This difference results from a decrease in the building’s period from 4.27 s to 1.43 s with the outrigger’s increased stiffness, leading to higher base forces. Plastic hinge formation is more limited in FVD than in steel outriggers. FVD and outrigger bracing systems reduce hysteretic damping caused by energy loss from crack friction to 23.8 % and 47.92 %, respectively, confirming the advantage of FVD as an effective retrofitting technique.