Seismic performance of irregular-plan structures with ideal Fluid Viscous Damper positioning: a comparative efficiency analysis

Irregular-plan buildings are particularly vulnerable to earthquake-induced damage because mass-stiffness eccentricity amplifies torsional response and concentrates deformation in perimeter structural elements. This study investigates the seismic performance of a 10-story L-shaped reinforced concrete building with extreme torsional irregularity (η > 1.4) located in Padang, Indonesia. The numerical model was developed to compare three Fluid Viscous Damper (FVD) placement configuration with a conventional undamped structure as a reference. Nonlinear Time History Analysis was performed using 11 ground-motion records representing shallow crustal, Benioff, and megathrust earthquakes matched with the Padang city design spectrum. Among the evaluated configurations, the corner placement strategy (ESS-A) achieved the highest performance, reducing the maximum inter-story drift ratio in the X direction by approximately 36% while requiring fewer dampers than ESS-C. A per-damper efficiency index, defined as the percentage reduction in inter-story drift divided by the number of installed dampers, was introduced to quantify placement effectiveness. ESS-A dissipated 62.55% of the input energy and achieved an efficiency of 0.881% per damper, whereas ESS-C dissipated 69.16% but achieved only 0.248% per damper. These findings demonstrate that optimized damper placement and parameter efficiency govern seismic performance more effectively than increasing damper quantity in torsionally irregular reinforced concrete buildings.