An analytical approach to free vibration analysis of multi‐outrigger–belt truss‐reinforced tall buildings

This paper deals with a new and simple mathematical model that may be used to determine natural frequencies and mode shapes of a multistory building that consists of a framed tube, a shear core and multi‐outrigger–belt trusses. The effect of outrigger–belt truss and shear core on a framed tube was modeled as a concentrated moment placed at outrigger–belt truss location, which acted in opposite direction of the rotation created by lateral loads. The analysis is based on a continuum approach, in which a tall building structure may be replaced by an idealized cantilevered beam to model the building's structural characteristics. Energy method and Hamilton's principle have been used to develop the governing equations. After applying separation of variables method to time and space variables, the resulting eigensystem was solved to obtain the building's natural modes and frequencies of vibration. A computer program has been developed in MATLAB (Mathworks Inc., CA, USA) environment, and a numerical example has been solved to demonstrate the accuracy of this method. Results obtained from the proposed mathematical model give a good understanding of a structure's dynamic characteristics. The method is simple to use yet reasonably accurate and hence suitable for quick evaluations during preliminary design stages. Copyright © 2011 John Wiley & Sons, Ltd.     

Simultaneous size and topology optimization of 3D outrigger‐braced tall buildings with inclined belt truss using genetic algorithm

To investigate the optimum location of the outrigger system, a metaheuristic‐based size and topology optimization of the outrigger‐braced tall buildings is carried out by various three‐dimensional structural frames with different shapes of belt trusses. By considering the elastic behavior, the whole elements of the structural models such as beams, columns, core, and trusses are optimized simultaneously in conjunction with the location of the outrigger. Furthermore, to reach more optimality, several novel types of belt truss are proposed having inclined and inverse‐inclined belt trusses with better structural and architectural features and optimum performance in comparison with the horizontal one. Different models with 25 to 40 stories having various span numbers are optimized using the genetic algorithm, and the results are compared with each other. In the modeling process, the exact wind load distribution is applied to the structure based on the ASCE7‐16 rather than the uniform or triangular ones. According to the results, the optimum cross‐sectional size and outrigger locations of different models are obtained, and it is indicated that the proposed novel belt trusses are optimal solution for the problem.     

Seismic performance of torsionally stiff and flexible multi‐story concentrically steel braced buildings

It is expected that application of torsion provisions in typical seismic codes shows different levels of efficiency for torsionally stiff and flexible buildings. This paper studies difference in performances of a range of code designed torsionally stiff and flexible five‐story building models. The models are classified in eight configurations to cover common range of buildings designed with the seismic provisions of Iranian Standard 2800 as a typical seismic design code. Seismic nonlinear dynamic time history behavior of eight building models subjected to seven horizontal bi‐directional design spectra compatible ground motions is investigated. These models cover a wide band of very torsionally stiff to very flexible buildings. Response parameters are element ductility demand and building story drift ratio. These criteria are appropriate indices for structural and nonstructural damages, respectively. The results indicate that the present linear static procedure of building codes such as the Iranian Standard 2800 is not generally adequate for structures with very low torsional stiffness. Copyright © 2012 John Wiley & Sons, Ltd.     

Analysis of outrigger‐braced reinforced concrete supertall buildings: Core‐supported and tube‐in‐tube lateral systems

This study is primarily focused on the approximate analysis of reinforced concrete outriggers which are commonly used in the design and construction of supertall buildings subject to distributed horizontal loads. Existing global analysis formulae that provide preliminary results for lateral deflections and moments are reviewed for two lateral load resisting systems, namely, core‐supported‐with‐outrigger (CSOR) system and less frequent tube‐in‐tube‐with‐outrigger (TTOR) system. These formulae are only applicable for CSOR and neglect the reverse rotation of the outrigger actually suffered due to the propping action from the outer columns and give rather high predictions of the deflections compared with advanced numerical finite element (FE) models. An improved model is proposed which overcomes this issue and provides more consistent results to FE predictions. The same can also be extended to TTOR. Several case studies are investigated to verify the accuracy of the proposed methodologies. The global analysis is followed by the local analysis of reinforced concrete outrigger beams using strut‐and‐tie modelling and non‐linear FE analysis to obtain optimized reinforcement layouts (reduction of quantities of reinforcement). The results highlight the different challenges in detailing such structural members which are heavily loaded (high congestion of reinforcement), and the behaviour at failure can be brittle.     

Vibration characteristics of tall buildings braced by shear walls and thin‐walled open‐section structures

An analytical method is presented for the three‐dimensional frequency analysis of buildings braced by shear walls and thin‐walled open‐section structures. Owing to the asymmetry of the structure, the centre of gravity and the centre of flexural rigidity of the floor plan do not coincide, and hence the flexural vibration in two mutually perpendicular directions and the warping torsional vibrations are all coupled. Based on the continuum approach and D'Alembert's principle, the governing differential equation of free vibration and its corresponding eigenvalue problem for asymmetric shear walls and thin‐walled open‐section structures are derived. Based on the theory of differential equations, an analytical method of solution is proposed to solve the eigenvalue problem and a general solution is derived for determining the natural frequencies of the structures. Results obtained from the proposed method for the example structure show good agreement with those of finite element analysis. It is also shown that the proposed analysis is efficient and accurate enough to be used both at the concept design stage and for final analysis. Copyright © 2007 John Wiley & Sons, Ltd.     

Structural design and analysis of vertical double‐layer space structures in super‐tall buildings

This paper investigates the potential of double‐layer space structures to be applied vertically as a new structural system in super‐tall buildings. The investigation using case studies covers four stages: structural designs of 100‐storey buildings in order to obtain internal force distributions and determine appropriate structural member sizes, analyses of the impacts of wind and seismic loads on the structures, sensitivity of structural weight ratios and lateral deflection constraints to changing structural geometry, and comparison of the lateral deflected shapes and structural weights per unit area with those of other current tall structural systems. The results show that changing the angles of diagonal members to make them span two storeys rather than one storey reduces structural weight and has little impact on lateral deflection. Compared with other current tall structures, vertical double‐layer space structures are relatively efficient structurally. The study concludes that double‐layer space structures can be applied vertically as a structural system of super‐tall buildings. Copyright © 2012 John Wiley & Sons, Ltd.     

Structural performance and economics of tall high strength RC buildings in seismic regions

For a multitude of economic and societal considerations, high rise structures are on the increase. This in turn promotes the use of high strength materials to reduce column size and construction times. Whereas design guidance and engineering understanding of high strength RC structures under static loading is well‐developed, little work has been undertaken on the economics of whole buildings and their performance under earthquake loading. In this paper, 10 buildings of 24 stories are designed and detailed according to modern seismic codes. The buildings are all nominally equivalent, using a stiffness equivalence criterion and its derivatives. The cost of construction is compared in terms of steel, concrete and formwork. The static inelastic response of the buildings is also assessed, followed by a full nonlinear dynamic analysis of all buildings using three earthquake records at the design acceleration and twice the design value. Comprehensive assessment of the static and dynamic results is undertaken. It is concluded that the cost increase is mainly due to the steel, whilst significant member reductions may be availed of by using high strength concrete. The behaviour of high strength concrete structures is not inferior to that of normal strength materials. Indeed, it is observed that lower levels of overstrength can be achieved in high strength materials than in their normal strength counterparts, mainly due to the over‐reinforcement of the latter to resist vertical forces. Recommendations on the use of equivalent cracked stiffness for period calculation in design, and also effective periods for use in displacement‐based design, are given. Copyright © 1999 John Wiley & Sons, Ltd.     

The wind‐induced response characteristics of atypical tall buildings

A tall building reacts sensitively to winds because the wind force increases according to the height and shape of the building. Various shapes of tall buildings and their aerodynamic characteristics have been studied extensively. For structural design and occupant comfort, the dynamic displacement of a tall building must be maintained within the criteria for acceptable levels of wind‐induced motion. An aerodynamically appropriate building shape needs to be selected at the design stage of a tall building. In this study, wind‐induced vibration responses were investigated, according to the criteria for maximum acceptable displacement and acceleration. Copyright © 2007 John Wiley & Sons, Ltd.     

Drift design of steel‐frame shear‐wall systems for tall buildings

Drift design methods based on resizing algorithms are presented to control lateral displacements of steel‐frame shear‐wall systems for tall buildings. Three algorithms for resizing of structural members of the steel‐frame shear‐wall systems are derived by formulating the drift design process into an optimization problem that minimizes lateral displacement of the system without changing the weight of a structure. During the drift design process, cost‐effective displacement participation factors obtained by the energy method are used to determine the amount of material to be modified instead of calculating sensitivity coefficients. The overall structural design model with the drift design method for the steel‐frame shear‐wall systems is proposed and applied to the structural design of three examples. As demonstrated in the examples, the lateral displacement and interstorey drift of a frame shear‐wall system can be effectively designed by the drift design method without the time‐consuming trial‐and‐error process. Copyright © 2002 John Wiley & Sons, Ltd.     

Design and seismic response of tall chevron panel buckling‐restrained braced steel frames

The numerical analysis of the seismic performance for tall chevron panel buckling‐restrained braced steel frames (PBRBFs) under small and strong earthquake excitations has been carried out to investigate a capacity design procedure for chevron PBRBFs and to examine the effects of axial strength distribution of braces along the height of buildings, vertical supports of braces for the braced beams and the overstrength of braces on the seismic response of PBRBFs. It revealed that the chevron braces that remained elastic can actually provide the vertical supports for the braced beams. Under severe earthquake excitations, the vertical supports deteriorated greatly after braces yielding. The PBRBFs designed by omitting vertical supports of braces for the braced beams and considering the overstrength of braces exhibited superior performance with smaller plastic deformations for braced beams and reduction in ductility demands for panel buckling‐restrained braces (PBRBs) as compared with the others. The distribution of yielding for PBRBs in 10‐story buildings verified that the participation from the higher modes is not very remarkable and that the capacity design based on the first‐mode response can be considered for multistory PBRBFs. Moreover, on the basis of the analysis results of the 30‐story PBRBF, the participation of the higher modes should be taken into account for high‐rise PBRBFs. Copyright © 2011 John Wiley & Sons, Ltd.     

Identification of the mode shapes of spatial tall multi‐storey buildings due to earthquakes: the new ‘modal time‐histories’ method

In the present article, a new method is presented which attempts to identify the dynamic characteristics (eigen frequencies, eigen periods, mode shapes and modal damping ratios) of spatial asymmetric tall multi‐storey buildings through measured seismic responses (accelerations). This new method is entitled ‘method of modal time‐histories’, because its main target is to identify the modal time‐histories of accelerations that are obtained by accelerograms recorded on the points of buildings where suitable accelerometers have been installed. In the case of an earthquake, the multi‐channel local network of accelerometers records the time‐histories of the accelerations of the building. In addition, in order to have a successful outcome, the instrumentation form of the multi‐channel local network on the building can potentially play the most important role. This paper, first, presents a relevant mathematical analysis that is adapted to the instrumentation form applied to the multi‐storey buildings and, second, outlines the new method, which consists of nine steps. Finally, in order to illustrate the theory, a suitable numerical example of an instrumented asymmetric five‐storey r/c building that has been oscillated by a weak earthquake is also provided. On the one hand, the identification of the dynamic characteristics of spatial asymmetric buildings contributes to the removal of the uncertainties of building models in order to perform advanced non‐linear analyses about inherent building seismic capacity. On the other hand, this method supports the simple monitoring of a building's ‘structural integrity’. Copyright © 2010 John Wiley & Sons, Ltd.     

Reduced order control for wind‐induced vibrations of tall buildings

The design of a structural control system for a tall building may not be easy owing to the large number of degrees of freedom involved. Obviously, it is much easier to design a structural control system for the reduced‐order system than for the full‐order system. Model reduction is thus useful when control systems are implemented in civil engineering structures. A reduced‐order modelling technology for vibration control of wind‐excited tall buildings is presented and its performance is studied. The important issues associated with wind‐induced vibrations, model condensations and reduced‐order control are addressed. Finally, a numerical example, a tall building with an active tuned mass damper or a passive tuned mass damper, is given to show the efficiency of the reduced‐order control technique. Copyright © 2003 John Wiley & Sons, Ltd.     

A global approach for three‐dimensional analysis of tall buildings

In the literature, several approximate approaches have been proposed to analyse the lateral loading distribution of external loads in high‐rise buildings; in this paper, a general method is proposed for the analysis of the lateral loading distribution of three‐dimensional structures composed of any kind of bracings (frames, framed walls, shear walls, closed and/or open thin‐walled cores and tubes) under the customary assumption of floor slabs being undeformable in their planes. This general formulation allows analyses of high‐rise structures by taking into account the torsional rigidity of the elements composing the building without gross simplifications, even in the case of very complex shapes and with the contemporary presence of different kinds of bracing. The method is aimed at gaining an insight into the force flow in the structure, in order to understand how the building response is governed by decisive structural parameters and to compare preliminary calculations with other approaches such as the structural finite element analysis. Copyright © 2009 John Wiley & Sons, Ltd.     

Wind‐induced vibration control of tall buildings using hybrid buckling‐restrained braces

A buckling‐restrained brace (BRB) is a system with excellent earthquake‐proof performance, but it does not dissipate energies caused by the load from weak earthquakes or winds. A hybrid BRB (H‐BRB), which improved the performance of the BRB, is a type of composite damper system consisting of a BRB and a viscoelastic damper. To explain the wind‐induced vibration control performance of H‐BRB, a 40‐story steel building was designed and used as an analysis model in this study, on the basis of the damping ratio from a structural performance test, using normal steel braces, BRB and H‐BRB. In addition, to evaluate the optimal location of H‐BRB, a time‐history analysis of four models was conducted in the study. For such time‐history analysis, wind‐load data in a 10‐year recurrence interval, which were calculated from the wind tunnel test, were used. The result of the time‐history analysis showed that H‐BRB is effective in improving both the lateral stiffness and serviceability of a building using the existing BRB. It also confirmed that it is most effective to position H‐BRBs mainly on the lower stories. Copyright © 2012 John Wiley & Sons, Ltd.     

On modelling of typhoon‐induced non‐stationary wind speed for tall buildings

Typhoon‐induced wind around tall buildings may not be stationary because it is a large body of rotating air. A new approach is thus proposed in this paper for characterizing typhoon‐induced wind speed. Typhoon‐induced non‐stationary wind speed is modelled as a deterministic time‐varying mean wind speed component plus a zero mean stationary fluctuating wind speed component. The time‐varying mean wind speed is naturally extracted from the measured wind speed time history using empirical mode decomposition (EMD). Wind characteristics described in the traditional approach based on a stationary wind model are redefined and extended in the non‐stationary wind model. The new approach is then applied to wind data measured at the Di Wang building during Typhoon York. The results show that most of recorded wind samples are non‐stationary but they can be decomposed into a time‐varying mean wind speed component plus a well‐behaved zero mean fluctuating wind speed component admitted as a stationary random process with Gaussian distribution. Other wind characteristics such as probability distribution of fluctuating wind speed, turbulence intensity, gust factor, and wind spectrum obtained by the new approach seem to be more realistic than those gained by the traditional approach. Copyright © 2004 John Wiley & Sons, Ltd.     

Optimum seismic design of steel framed‐tube and tube‐in‐tube tall buildings

The relatively large number of structural elements and the variety of design code requirements complicate the design process of tall buildings. This process is exacerbated when the target is to obtain the seismic code‐compliant optimal design with minimum weight. The present paper aims at providing a practical methodology for the optimal design of steel tall building structures considering the constraints imposed by typical building codes. The applicability of the proposed approach is demonstrated through the determination of the optimal seismic design for 20‐, 40‐, and 60‐story buildings with a framed tube as well as a tube‐in‐tube system. Such a design gives rise to a basis for the fair comparison of the behavior of the framed tube with that of the tube‐in‐tube system under applied loads. The optimal weight of the buildings with the tube‐in‐tube system turns out to be slightly less than that of the buildings with the conventional framed‐tube system.     

Convolutional neural network‐based wind‐induced response estimation model for tall buildings

This study presents a convolutional neural network (CNN)‐based response estimation model for structural health monitoring (SHM) of tall buildings subject to wind loads. In this model, the wind‐induced responses are estimated by CNN trained with previously measured sensor signals; this enables the SHM system to operate stably even when a sensor fault or data loss occurs. In the presented model, top‐level wind‐induced displacement in the time and frequency domains, and wind data in the frequency domain are configured into the input map of the CNN to reflect the resisting capacity of a tall building, the change in the dynamic characteristics of the building due to wind loads, and the relationship between wind load and the building. To evaluate stress, which is used as a safety indicator for structural members in the building, the maximum and minimum strains of columns are set as the output layer of the CNN. The CNN is trained using measured wind and wind response data to predict the column strains during a future wind load. The presented model is validated using data from a wind tunnel test of a building model. The performance of the presented model is verified through strain estimation with data that were not used in the CNN training. To assess the validity of the presented input map configuration, the estimation performance is compared with a CNN that considered only the time domain responses as input. Furthermore, the effects of the variations in the configuration of the CNN on the wind response estimation performance are examined.     

Modeling of two‐cell cores for three‐dimensional analysis of multi‐story buildings

The reliability of simplified models for single‐cell cores, and particularly for open and semi‐open U‐cross‐section cores, has been the subject of many research papers in the recent past. In contrast, on an international level, only little mention has been made of the efficiency of such models for multi‐cell cores of multi‐story R/C buildings. This paper evaluates and comments on the reliability of several simplified models for open two‐cell cores that are often used in practice. The models examined are: (a) models composed of equivalent columns in alternative configurations; (b) models composed of panel elements; and (c) finite shell element models with one element for each flange in each story. These models are compared with one another and with the solution considered accurate, which is the one obtained by using a finite element method consisting of an adequately dense mesh of finite shell elements. The conclusions obtained refer to both the simplified modal response analysis and the multi‐modal response spectrum analysis, while the specific assumptions for the numerical investigations are compatible with the provisions of modern seismic design codes. Copyright © 2000 John Wiley & Sons, Ltd.     

Influence of non‐structural components on lateral stiffness of tall buildings

A building is a complex assemblage of both structural and non‐structural components (NSC). Although many NSC, such as partition walls, external walls, parapet walls, stairwells, elevator shafts and so forth, are connected directly to the structural system, their behaviour and stiffening effects under lateral loading have normally been ignored by design engineers, despite significant advances in computer technology and the availability of modern computational resources. The performance of structures can be greatly improved by the increase in strength arising from the NSC; on the contrary, this increase in strength also accompanies an increase in the initial stiffness of the structure, which may consequently attract additional seismically induced lateral inertia forces. This paper is concerned with the estimation of the lateral stiffness contributed by the NSC to the total stiffness of three common forms of tall building structures constructed in Hong Kong. Both dynamic tests and numerical modelling of the buildings have been carried out for this purpose. Natural period estimates from dynamic tests and from analyses using calibrated finite element models were found to be in remarkable agreement. Significant stiffness contributions from NSC to the total lateral stiffness of tall buildings have been observed in the study. The extent of the contributions depends on the structural form and the type of components. Other contributions to the additional stiffness have also been analysed for comparison in the study. Copyright © 2005 John Wiley & Sons, Ltd.