A new method for modelling a tall building with an outrigger system is described. In this method, the high-rise building core structure is modelled with an Euler–Bernoulli beam considering second-order effects with a box section. The outrigger system is also considered by means of a rotational spring, the location of which is variable. Exact stability analysis of this model is then incorporated and the buckling load of the whole structure under only gravity load is obtained. Different values were considered for the distance of the outrigger system from the top of the structure. Using an analytical solution for the buckling load of the structure, the optimum location of the outrigger system was investigated. The core structure was modelled as a clamped Euler–Bernoulli beam. Thus, the exact stiffness matrix of a tapered beam was also obtained. The method can be used to determine the exact optimum location of an outrigger system based on stability analysis of structure.

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