Seismic performance and strengthened-storey optimization of super-tall outrigger buildings using braces with intentional eccentricity

Conventional steel-braced outrigger trusses are widely used to control lateral deformation in super high-rise buildings, but their high axial stiffness can create abrupt stiffness discontinuities at the strengthened story and amplify deformation and internal-force demands in adjacent stories. Braces with intentional eccentricity (BIEs) offer an alternative by partially decoupling stiffness from strength, enabling a flexible strength-stiffness design strategy without reducing ultimate brace strength. This study investigates a 71-story super high-rise building equipped with BIE outrigger trusses and compares it with an otherwise identical building using conventional steel-braced (CSB) outrigger trusses. The building is designed according to Chinese code requirements and assessed through response-spectrum analysis under frequent earthquakes and nonlinear time-history analysis under rare earthquakes. A preliminary method is also developed to estimate the optimal strengthened-story location by accounting for eccentricity-induced stiffness reduction. Results show that BIE outrigger trusses reduce abrupt deformation changes at the outrigger level, lessen internal-force amplification in adjacent beams and columns and promote uniform seismic deformation along the building height. Compared with CSB outriggers, the BIE system reduced the sudden change in inter-story drift near the strengthened story by approximately 58% and reduced wall-beam yielding by approximately 17% on average. Optimizing the strengthened-story location further reduced the maximum average story drift and increased the relative drift-control advantage of BIE over CSB. These findings indicate that BIE outrigger trusses can improve seismic resilience through controlled flexibility, enhanced energy dissipation and greater freedom in strengthened-story placement.