Steel Outrigger Bracing System Position Optimization for High Rise Construction

The outrigger bracing system provides the solution to control excessive drift and displacement in high rise buildings. It consists of the outrigger bracings or the outrigger trusses which connects the central core of the building with the peripheral columns and the peripheral columns relate to one another through the belt trusses. In this study, the conventional structural model having the central core of reinforced concrete and the models with outrigger at top, top and 0.75H, top and 0.5H and top and 0.25H where H is the total height of the building are modeled for the 20, 40 and 60 storey building heights. The main objective of the study is to determine the optimum location of the outrigger system. ETABS 2017 software package is used for the modeling and analysis of this study. The models are analyzed by three methods, Equivalent Static Method, Response Spectrum Method and the Non-Linear Time History Analysis and results are compared in terms of the maximum top displacement, storey drift, base shear, moment in the core, axial forces in peripheral column, roof acceleration, roof velocity and time period of the structure. The results obtained from different analyses suggests that the optimum location of the outrigger bracing system for high rise building is at the top and mid height of the building for which the top displacement and drift is minimum. The outrigger structures are stiffer than the conventional structures and hence time period decreases. The top and 0.5H model of outriggers showed the maximum decrease in moment at the base of the central core and the maximum increase in axial forces in peripheral columns because they are engaged with central core and forms a tension compression couple that resists external loadings.