Seismic assessment of super high-rise buildings strengthened with BIE outrigger trusses

Outrigger trusses configured by diagonal steel braces are widely used as strengthening storey mechanisms to counter seismic forces in super high-rise buildings. However, a critical drawback of outrigger trusses is their sudden amplification of storey stiffness, intensifying storey deformation and internal forces in adjacent storeys. Steel braces with intentional eccentricity (BIE) have been recently developed to overcome some of the shortcomings of conventional steel braces by offering a lower stiffness without scarifying section’s ultimate strength while providing higher post-yielding stiffness, ductility, and greater energy dissipation capacity. In the present paper a 77-storey super high-rise building strengthened with BIE outrigger trusses is designed. The design is selected on the basis of static wind and earthquake analysis and consists of a mixed concrete-steel structural system adopting concrete shear walls for the main core of the building, concrete-filled
steel tubes for the columns and I-shaped steel section for the beams. Response spectrum analysis results of the frequent event demonstrate the superiority of BIE used in outrigger trusses to reduce strength demands in beams and column of the adjacent storeys while successfully reducing storey deformation. Non-linear dynamic time-history analysis results of the rare event demonstrate that the BIE outrigger trusses can provide the required stiffness for the tall building to meet the target storey drift limitations. Compared with the conventional outrigger trusses, BIE outrigger trusses successfully reduced the average maximum inter-storey drift by 6%, the storey localized deformation by 70% and the yielding of peripherical gravity beams by 30% on average.