Composite Outrigger Structural System with Buckling Restrained Brace for High-Rise Building

Abstract

In the last few decades, increasing rate of urbanization together with the scarcity of urban land have made high-rise buildings an appropriate choice of city planners. The tall and iconic buildings attracted business and commercial activities as well as tourists and made them symbol of pride for the city and country. Denser urban areas with mega structures are preferable from an environmental point of view because of their efficiency in terms of land use and energy consumption. The present trend of tall building construction will play crucial role for the future of humanity and the ecosystem on the earth. When the height of the building is increased, the role of lateral load resisting system is becoming important compared to the gravity load resisting system. The shear wall and frame structural system is commonly used as lateral load resisting systems for buildings with 30 to 50 storeys. The main design criteria for high rise building are strength, stiffness, and ductility which are achieved by governing a lateral load resisting system. In order to limit the lateral drift criteria within the acceptance limit and to maintain human comfort with optimum utilization of material, the outrigger and belt-truss system is developed. In this structural system, the rigid horizontal beam, known as an outrigger, is connected to the shear wall core and the external columns. The outrigger is made of a rigid concrete deep beam or steel truss of one to two storey depth. The perimeter columns are connected with rigid beam or truss at outrigger location commonly known as belt-truss. While using the composite outrigger structural system, the benefit of using the properties of both the concrete and steel are achieved. In composite system, the building frame and central core are made of concrete and the outrigger is made of steel truss. When the cyclic lateral load is higher, the outrigger may fail due to buckling of compression members in the steel-truss. For solving this problem, a Buckling restrained brace is incorporated to replace the diagonal element in the steel truss of outrigger. The buckling restrained brace is used for resisting both the tension and compression forces as well as reducing lateral defection of the building and dissipation of energy. It is also used for strengthening the building. The Outrigger and belt-truss can be provided on a single story or multiple stories. It can be provided on one or multiple levels in the building. It is very effective in increasing the stiffness of the building and reducing the core bending moment and top story displacement. The present study aims to understand the behaviour of the outrigger structural system under lateral loading. The reduction in core bending moment, top storey displacement with variation in location of one or two outrigger is presented in report.