Torsional analysis of core structures in tall buildings

A folded plate analysis of the behaviour of core structures subjected to torsional loading is presented.In this method the core is assumed to consist of vertical plates rigidly connected together along their edges, and by using the engineering theory of bending in conjunction with the continuous connection technique for panels containing openings, the core behaviour has been represented by a third order linear differential equation.The method has been shown to be applicable to any core which is totally open or partially closed with lintelbeams. The general governing equation is expressed in terms of one unknown, the angle of rotation and a singlenon-dimensional stiffness parameter aH, the core relative stiffness. The influence of a stiffening element at thetop and flexibility of the foundations have been included.Solutions of the governing equation for three standard load cases, a point torque at the top, a uniformlydistributed torque and a triangularly distributed torque are given. A parameter study has been carried out toshow the interactive effects of the three fundamental parameters on the primary core actions when subjected tothe standard load cases. Design charts have been produced for the rapid evaluation of the core rotationsand internal forces. Consideration has been given to core structures with stiffness variations throughout theheight, special emphasis being given to the effects of a reduction of thickness of the walls at some level.