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 lintel beams. The general governing equation is expressed in terms of one unknown, the angle of rotation and a single non-dimensional stiffness parameter aH, the core relative stiffness. The influence of a stiffening element at the top 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 uniformly distributed torque and a triangularly distributed torque are given. A parameter study has been carried out to show the interactive effects of the three fundamental parameters on the primary core actions when subjected to the standard load cases. Design charts have been produced for the rapid evaluation of the core rotations and internal forces. Consideration has been given to core structures with stiffness variations throughout the height, special emphasis being given to the effects of a reduction of thickness of the walls at some level
