Seismic response control of base-isolated buildings equipped with diagonally oriented fluid viscous dampers under long-period ground motions

Long-period ground motions can induce excessive displacements in base-isolated (BI) buildings, often necessitating supplementary damping devices for response mitigation. Fluid viscous dampers (FVDs) are widely used for seismic energy dissipation. However, their limited axial stroke capacity may require large devices to accommodate substantial displacement demands, which can be impractical. One potential solution is the diagonal installation of FVDs, which alters the force–displacement relationship and reduces stroke demand. This study investigates the seismic performance of BI buildings equipped with diagonally oriented FVDs under long-period ground motions. Two BI buildings, with 5 and 15 stories, were designed in accordance with Japanese seismic provisions and analyzed using nonlinear time-history analysis. Five representative long-period ground motions, scaled to level 2 earthquake intensity, were considered. The influence of the initial installation angle of FVDs on displacement, inter-story drift, acceleration, shear force, and axial stroke demand was evaluated. The results indicate that the installation angle has significant impact on seismic response characteristics. Larger angles, approaching horizontal installation, effectively reduce isolation layer displacement but increase inter-story drift, acceleration, and axial stroke demand. Conversely, smaller angles mitigate drift and stroke demand while resulting in larger isolation displacements. For equivalent damper force capacity, smaller angles require greater number of dampers but permit the use of short-stroke devices, whereas larger angles reduce the number of devices at the expense of increased stroke demand and superstructure response. These findings demonstrate that diagonally oriented FVDs provide a practical strategy for controlling the seismic response of BI buildings under long-period ground motions. • Seismic responses comparison of BI buildings equipped with diagonally oriented FVD were studied. • The possibility of implementing short-stroke FVD for base-isolated buildings was examined. • The effectiveness of FVD with various installation angles to control the excessive displacement under long-period earthquakes was discussed.