Estimating period ratio for predicting torsional coupling

An approximate method of estimating the uncoupled period ratio for use in predicting the degree of translational-torsional coupling of mixed-bent type multistorey building structures subject to dynamic loading is presented. The method uses the parametric continuum approach and is based on the generalized representation of asymmetric wall-frame structures by shear-flexure torsion-warping cantilevers. It is applicable to structures consisting of any combination of walls and frames that are uniform with height. A code-type simple yet reasonably accurate formula for estimating the uncoupled period ratio on the basis of the preliminary design information is proposed. The required preliminary information includes the plan geometry, the primary structure member sizes, the mass distribution and the building height. The significance of the uncoupled period ratio in the assessment of the coupling effect and its implicit involvement in certain code recommendations are discussed. The derivation of the method and comparisons of results with those obtained by 3D finite element dynamic analyses of discrete member models are given. A worked numerical example illustrates the application of the method.