Locating optimum torsion axis in asymmetric buildings subjected to seismic excitation

Abstract

Seismic torsional effects in buildings are attributed to the distance between the centres of mass of the floor slabs and the centres of rigidity of the building. Various procedures have been developed to locate these points, but their scattering over the height of the structure makes their use very difficult in implementing the code torsional provisions. As an alternative, the concept of the optimum torsion axis has been introduced: a vertical axis through which application of lateral in-plane forces would cause minimum torsional response. A convenient method is presented for the determination of this axis by means of the discrete-element approach (stiffness method) and its accuracy is demonstrated in common building structures with mass and stiffness irregularities.