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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.

A method to predict the degree of translational-torsional coupling of mixed-bent-type multistory building structures subject to dynamic loading is presented. The method is based on the treatment of nonproportionate structures as a particular class of regular proportionate ones, and on the generalized representation of asymmetric structures by shear-flexure, torsion-warping cantilevers. The method is applicable to structures consisting of any combination of walls and frames that are uniform over their height. The concept and location of the significant centers of reference, such as the shear centers and the centers of resistance, of mixed-bent-type multistory building structures are clarified, and the significance of the coupled-period ratio for the assessment of the coupling effect is discussed. The derivation of the method, and comparisons of results with those obtained by three-dimensional (3D) finite-element dynamic analyses of discrete member models, are given. A worked example illustrates the applica...

Over the past decade, one of the most remarkable advances in tall building design has been their construction to unprecedented slenderness ratios. In this paper, the authors review some of the basic and innovative structural framing arrangements that have been found from first-hand experience to be particularly appropriate to so-called ‘sliver’ buildings. Also, case studies of four landmark New York City buildings are presented in which some of these framing concepts have been applied.

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.

The lateral load resistance of tall wall-frame building structures comprising a combination of moment-resisting frames and shear walls that are reduced in size or terminated entirely at intermediate heights is investigated. A generalized theory for the deflection of such structures is developed on the basis of a continuum model, to show that curtailment of the walls is not necessarily detrimental to the performance of the structure. Indeed, if the walls are curtailed within a certain height region the forces in the upper part of the frame are reduced while the top deflection is negligibly affected. An expression for the deflection of curtailed uniform wall-frame structures is minimized to provide guidance for the optimum level of wall curtailment to cause a minimum increase in the top deflection. Guidance on the level of curtailment without detriment to the structure’s performance for practical nonuniform wall-frame structures is given.

The results of a theoretical investigation of the effects of architectural precast concrete cladding panels on the static wind load response of representative tall building structures are presented. On the basis of deductions from a previously reported detailed study of a cladding panel interacting with a moment-resisting frame, analyses of complete clad structures are made with the panels represented in the models of the structures by equivalent bracing members. The displacements, deflected shapes and member forces resulting from static wind load three-dimensional analyses of the structures, with and without the effects of the panels, are compared and discussed. In providing additional stiffness to the structures, the cladding panels attract loads, some of which exceed the design loads of the panels. The capabilities of the panels and their connections to withstand the induced loads are also discussed. Finally, a procedure for the analysis of the buildings braced by precast concrete cladding panels is proposed.

The paper describes a study of the interaction that occurs between moment-resisting reinforced concrete or steel frames and precast concrete cladding panels when such buildings, designed according to current practice, are subjected to horizontal loading. The significant structural parameters are identified and their relative importance in influencing the racking stiffness of the structure is investigated. A simple model for representing the panels in the total structure model is proposed. The structure model may then be analyzed by computer using a general purpose structural analysis program to provide the horizontal deflections, and the forces in the frame, panels and their connections.

A method of constructing a planar model for the analysis of relatively complex three‐dimensional tall‐building structural systems is proposed. The buildings may be asymmetric in plan, and composed of orthogonal intersecting bents of any type. Bent properties and configurations may vary throughout the height. No transformations of bent properties or analysis results are required. The model consists of all the bents, from both orthogonal directions, assembled in a single plane and joined by a mechanism in the plane. The mechanism causes the response of the bents in the single plane to duplicate their relative response in the three‐dimensional structure.

An approximate method for determining the seismic base shear of high‐rise building structures on the basis of the preliminary design information is presented. The method is based on the generalized representation of the family of shear‐flexure cantilevers by the coupled‐wall theory, and is applicable to nontwisting structures consisting of any combination of walls and frames that are uniform with height. Such structures include coupled shear walls, walls connected by beams to columns, and wall‐frame structures. The static and dynamic behavior as well as the geometric and material properties of shear‐flexure cantilevers are fully described in terms of two nondimensional characteristic parameters. A decoupled eigenvalue approach is used to evaluate the base shear coefficients corresponding to the first two periods of free vibration. The derivation of the method as well as a comparison of its results with those obtained by earlier approximate methods and by a discrete finite element dynamic analysis are give...

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.

An approximate method for estimating the drift of multi-bent structures is presented. Structures that are singly or doubly symmetrical in plan and comprising any combination of shear walls, coupled walls, rigid frames and braced frames, can be considered. Results for structures that are uniform with height compare closely with results from stiffness matrix computer analyses. The method is developed from coupled-wall deflection theory which is expressed in terms of two non-dimensional structural parameters. The parameters involve three structural properties: the individual bending stiffness of the walls, the overall bending stiffness related to axial deformations of the walls and racking stiffness caused by reverse bending of the beams. Similar properties are calculated for rigid frames, braced frames and shear walls and then combined to determine values of the two parameters for the total structure. These values are then substituted into a generalized equation to obtain the deflection profile. This method accounts for axial deflection of the vertical components and is, therefore, more accurate for very tall structures. The method provides a rapid estimate of the drift in a high-rise structure as well as allowing an easy means of comparing the suitability of different structural solutions for a tall building. The method also illustrates the fundamental dependence of the behavior of continuous type cantilevers on two characteristic parameters.

A hand method of estimating the period of free vibration of building structures, for use in determining the minimum base shear for their earthquake design, is presented. The method is for structures that have uniform properties through their height, and that are symmetrical in plan and symmetrically loaded so that they do not twist. The structures may consist of rigid frames, coupled walls, wall-frames and braced frames, or any combination of these. The basis of the method is that all of the above described types of bent behave as members of a family of shear-flexure structures whose static deflections can be predicted by coupled wall theory. A method of decoupling the static deflection into a flexural component and a shear plus flexure wall-frame type of component is extended to dynamic behavior of a corresponding decoupled eigenvalue approach, to determine the periods of free vibration. The derivation of the method, an assessment of its accuracy, and a worked example to illustrate its application are presented.

The trend towards more slender and lighter building structures has resulted in potentially more significant P-delta effects; this has led to the demand for simple and accurate methods of P-delta analysis. Methods are reviewed and compared in terms of their efficiency and accuracy. Considered roughly in their order of sophistication, the methods reviewed include the amplification factor method, the direct method, the iterative method, the negative property member methods, and the second-order computer program method. In addition to these, a new method similar to the iterative method, but based on analyses using the actual gravity loading applied to successive deflected shapes, is presented. The results are identical to those given by the iterative method, while the analysis takes less than one-third of the time. Factors that differentiate the methods include their accuracy, ease of use, whether they are for hand or computer use, and whether they are applicable to all types of structures or only to certain types.

A hand method of analysis is presented for the torsional warping behavior of nonplanar asymmetrical systems of shear walls such as the elevator and service shafts in tall buildings. The method is suitable for both uniform and nonuniform walls with or without constraining lintels, or internal floor slabs, or both. The basic governing equations are derived, and used to construct non-dimensional curves which allow the direct analysis of uniform open-section walls subject to uniformly distributed torsional moment. The transfer matrix method is used to extend the method for the hand analysis of nonuniform wall systems. The results for uniform and nonuniform examples are shown to compare closely with those obtained by a more exact computer analysis.

An investigation of the behavior of diagonally-loaded square infilled frames is described first. Series of experiments on diagonally-loaded models with a range of frame stiffnesses indicated that a small increase in frame stiffness has a magnified effect on the over-all stiffness and strength of the structure. Approximate theoretical analyses, based on the length of contact between the frame and infill, are developed to explain this composite behavior, and to provide methods of predicting the over-all diagonal stiffness and strength. The behavior of laterally-loaded infilled frames is considered next. The methods proposed for the diagonally-loaded case are adapted to predict the lateral stiffness and strength of single or multi-story square infilled frames. The results of experiments on single and double-story models support the pro-posed methods of prediction.

Methods for predicting approximate lateral stiffness of single and multistory frames; stiffness of frames is considered by assuming equivalent diagonal strut to replace infill; effective width for equivalent strut is derived theoretically and checked by model experiments.

The validity of the concept that the shear strength of brickwork depends on a combination of the bond shear strength and frictional resistance in the mortar layers is questioned on account of inconsistencies revealed by earlier series of experiments. As an alternative approach the writers suggest that the shear strength may be dependent on the tensile strength of the mortar layers. Assuming that failure occurs when the principal tensile stress in the mortar equals its tensile strength, finite element stress analyses are conducted to determine the maximum principal tensile stresses in brickwork triplets resulting from applied shear and normal compressive forces. Failure curves are constructted relating the theoretical shear strength and normal compressive stress on the triplet for different modular ratios. Experimental results of shear tests on brickwork triplets, with varying normal compressive stress, are compared with the corresponding theoretical curve to provide support for the writers' proposition.

The behaviour of multi-storey infilled frames with rectangular infills and different beam and column sections is examined for the case of lateral loading. The members of the frame are rigidly connected together, and the infills, which are not bonded to the frame, are of a homogeneous, isotropic material. Approximate theoretical methods, based on an equivalent strut concept, are developed to predict the lateral stiffness and strength, and are substantially verified and partly modified by the results of four series of experiments. It is shown that the lateral stiffness and ultimate strength are dependent on the relative stiffness of the column and infill, but practically independent of the beam stiffness.

A relatively simple hand method is presented for the static and dynamic analyses of uniform structures consisting of interacting shear walls and frames with effectively planar loadings and deformation. The method is applicable also to the static analyses of non-uniform shear wall-frame structures in which step changes of properties occur at several elevations in the height of the structure. Examples are given to show that the method provides results which compare closely with those obtained from more exact but lengthier methods of analysis. Design curves which further simplify the hand computation are also included.

As far as the writers are aware, it is not generally appreciated that the effects of twisting actions on symmetrical structures may also be described by an equivalent plane frame action, and it is the object of this note to illustrate how this may be achieved. Equations are presented. The technique allows the analysis to be performed by standards plane frame computer programs, the appropriate stiffness transformations being carried out on the input data by the simple expedient of factoring the areas and second moments of area of the members.

A method of two-dimensional modelling for the analysis of symmetrical structures subjected to eccentric transverse loading is presented. The three-dimensional behaviour of the structure is decomposed into separate translational and twisting behaviour under the respective transverse and torque loadings. A two-dimensional model is formed and analyzed for each mode of behaviour and the results are combined to represent the total behaviour of the structure. The method is suitable for structures consisting of bents parallel to the direction of transverse loading. The bents can be of any type and may vary in their properties over the height. Key words: structural analysis, symmetrical structures, two-dimensional model.

SUMMARY The nature of the composite action which occurs when an infilled frame is subjected to in-plane loading is examined. It is assumed that the function of the infill can be represented approximately by struts along the compressive paths of the load through the infill. The stiffness and strength of the infill are then shown to be functions of the relative stiffness of the frame and infill and capable of being expressed graphically in terms of this parameter. Three types of infilled frame investigated by the author are described and the way in which the general proposition is applicable to each of them is explained.