Bryan Stafford Smith

Stiffened-story wall-frame tall building structure

Abstract This paper proposes a new concept to increase the lateral stiffness of wall-frame tall building structures by stiffening a story of the frame system either at the top or at an intermediate optimized level. The shear rigidity of the frame system is increased in a story level by infilling one or more bays of the frames in that story with concrete or masonry panels, or adding bracing to the story, or increasing the sizes of the columns and girders surrounding the story. The efficiency of the concept and the evaluation of the parameters involved in the behaviour of a stiffened-story structure are demonstrated with the help of a continuum model solution. The authors show that in some structures the lateral stiffness could be increased by as much as 70%. The technique is then applied to an example structure which is analysed both with the continuum model and a stiffness matrix solution.

Estimating period ratio for predicting torsional coupling

Abstract 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.

Two-beam model for static analysis of mono-symmetric thin-walled cantilevers

Abstract A model for the approximate analysis of mono-symmetrical thin-walled cantilever members subjected to transverse loads is presented. It is appropriate for the analysis of uniform or varying-section members, and it can be used with widely available structural analysis computer programs. The model comprises two simple beams located on one of the principal axes of bending and on opposite sides of the shear centre of the member. It accounts for bending as well as the St Venant and warping-torsional modes of behaviour. A newly devised transition mechanism provides for complete continuity in the model where the thin-walled member changes section. This allows changes in both properties and the locations of the shear centre to be properly represented. Numerical examples comparing the proposed two-beam model with the more complex shell element model are presented. The results for displacements and rotations from the two-beam model are acceptably close to those obtained from the shell element model; the discrepancies in stresses are greater but are not excessive for many practical purposes. The model is well-suited for use by designers in the approximate static analysis of thin-walled cantilever spars and for the elevator cores of tall building structures.