Behaviour of Outrigger Beams in High rise Buildings under Earthquake Loads

Tall building development has been rapidly increasing world wide introducing new challenges that need to be met through engineering judgment. In modern tall buildings, lateral loads induced by wind or earthquake are often resisted by a system of coupled shear walls. But when the building increases in height, the stiffness of the structure becomes more important and introduction of outrigger beams between the shear walls and external columns is often used to provide sufficient lateral stiffness to the structure. In general, earthquake ground motion can occur anywhere in the world and the risk associated with tall buildings, especially under severe earthquakes, should be given particular attention, since tall buildings often accommodate thousands of occupants. It is conceivable that structural collapse of such buildings can lead to disasters of unacceptable proportions. When adopting outrigger beams in building design, their location should be in an optimum position for an economical design. A range of different strategies ha s been employed to identify the optimum location s of these outrigger beams under wind load. However, there is an absence of scientific research or case studies dealing with op timum outrigger location under earthquake loads. This study aims to identify the optimum outrigger location in tall buildings under earthquake loads. A 50 storey building was investigated and three different peak ground acceleration to peak ground velocity ratios in each category of earthquake records were incorporated in this research study to provide a consistent level of approach . Response spectrum analysis was conducted and the behaviour of the building was determined considering response parameters such as lateral displacement and inter storey drift . It has been shown from this study that the structure is optimised when the outrigger is placed between 22-24 levels. Therefore it can be concluded that the optimum location of the structure is between 0.4 4-0.48 times its height (taken from the bottom of the building).

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