Invariant torsion properties of multistorey asymmetric buildings

In this paper significant invariant torsion properties of multistorey asymmetric diaphragm systems are presented and investigated, which do not depend on certain special characteristics of the structural system, but only on the vertical distribution of the lateral loading. The analytical study includes generalization of the application of existing formulas for finding the exact location of the optimum torsion axis, verification for its uniqueness, evaluation of the principal torsion directions for any position of the loading axis, and especially for the position of the optimum torsion axis. It also provides quantitative criteria to ascertain whether the diaphragm rotations in general are sufficiently small, when static analysis procedures of calculating the seismic response are going to be applied. Several numerical examples demonstrate the applicability of the proposed methodology, which helps to a better understanding of the torsional behaviour of multistorey buildings. Copyright © 2007 John Wiley & Sons, Ltd.