Q235 / Q345 Steel Prefab outriggerstructural system Multi Storey Steel Structures NZ Standard

Outriggers are interior lateral structural systems provided to improve the overturning stiffness and strength of high-rise buildings. It is a lateral load resisting system that is located within the building. The whole system consists of a core structure connected to the perimeter columns of the building using structural members called outriggers. The outriggers can be in the form of horizontal beams, truss, or walls. Outrigger systems can be made of any material of concrete, steel, or composite. With these structural systems, uplift and tension forces can be reduced significantly throughout the columns and foundations. The spacing of the outside columns can be driven by architectural and functional considerations, not structural considerations. The structural system reduces the overturning moments and provides greater efficiency in resisting forces. Outrigger engages the perimeter columns in lateral load resisting action which would otherwise act as a gravity load resisting elements

High-rise buildings are subjected to large lateral deformation either due to wind or seismic loads. The core structure of a high-rise building is subjected to cantilever deformation, while the frame structures surrounding the core are subjected to portal type deformation. This causes high drift and overturning effects on the structure.

The incorporation of outriggers efficiently controls the excessive drift due to lateral loads. This, hence, allows to prevent structural and non-structural damage in the structure. As shown below, outriggers reduce the core moment from top to down under the lateral load.

The structural action of outrigger systems in high-rise buildings is based on the tension-compression couple induced in the outer columns, as shown in figure. Under the action of lateral loads, a structure without any lateral support system is subjected to overturning.