Seismic performance evaluation of single damped-outrigger system incorporating buckling-restrained braces

The outrigger system is an effective means of controlling the seismic response of core-tube type tall buildings by mobilizing the axial stiffness of the perimeter columns. This study investigates the damped-outrigger, incorporating the buckling-restrained brace (BRB) as energy dissipation device (BRB-outrigger system). The building's seismic responses are expected to be effectively reduced because of the high BRB elastic stiffness during minor earthquakes and through the stable energy dissipation mechanism of the BRB during large earthquakes. The seismic behavior of the BRB-outrigger system was investigated by performing a spectral analysis considering the equivalent damping to incorporate the effects of BRB inelastic deformation. Nonlinear response history analyses were performed to verify the spectral analysis results. The analytical models with building heights of 64, 128, and 256 m were utilized to investigate the optimal outrigger elevation and the relationships between the outrigger truss flexural stiffness, BRB axial stiffness, and perimeter column axial stiffness to achieve the minimum roof drift and acceleration responses. The method of determining the BRB yield deformation and its effect on overall seismic performance were also investigated. The study concludes with a design recommendation for the single BRB-outrigger system.