Analysis of outrigger numbers and locations in outrigger braced structures using a multiobjective genetic algorithm

Due to its advantages, the outrigger braced system has been employed in high‐rise structures for the last 3 decades. It is evident that the numbers and locations of outriggers in this system have a crucial impact on the performance of high‐rise buildings. In this paper, a multiobjective genetic algorithm (MGA) is applied to an existing mathematical model of outrigger braced structures and a practical project to achieve Pareto optimal solutions, which treat the top drift and core base moment of a high‐rise building as 2 trade‐off objective functions. MATLAB was employed to explore a multiobjective automatic optimization procedure for the optimal design of outrigger numbers and locations under wind load. In this research, various schemes for the preliminary stages of design can be obtained using MGA. This allows designers and clients easily to compare the performance of structural systems with different numbers of outriggers in different locations. In addition, design results based on MGA offer many other benefits, such as diversity, flexible options for designers, and active client participation.     

An inter‐story drift‐based parameter analysis of the optimal location of outriggers in tall buildings

Outriggers are usually added in structural systems of tall buildings to collaborate central shear walls with peripheral columns. With outriggers, the structural overturning moment can be balanced, and the inter‐story drift can be controlled under horizontal loads. Therefore, the optimal location of outriggers plays a very important role in controlling the behavior of the whole building. Existing research has focused on the optimal position of outriggers on the base of the structural roof deflection. In the engineering practice, however, inter‐story drift is the most important target to control the design of tall building structures. This paper investigates the theoretical method of inter‐story drift‐based optimal location of outriggers. A Matlab program is written to perform the parameter analysis of optimal location of outriggers. Take a 240‐m tall building for a target building, the optimal location of one to three sets of outriggers under wind and earthquakes is obtained and can be utilized for the structural preliminary design of tall buildings. Copyright © 2015 John Wiley & Sons, Ltd.     

Structural performance of multi‐outrigger‐braced tall buildings

The optimum designs of multi‐outriggers in tall building structures are presented and discussed in this paper, through the analysis of structural performance of outrigger‐braced frame‐core structures. The influences of the locations of outriggers and the variations of structural element stiffness on the base moment in core, top drift and fundamental vibration period of such tall building structures are analysed in detail. A non‐linear optimum design procedure for reducing the base moment in the core is presented based on the penalty function method. The computer programs are developed on the basis of the proposed methods for analysing the behaviour and optimum design of multi‐outrigger structures. A series of figures presented in this paper can be used for the design purposes of outrigger‐braced tall building structures. Copyright © 2003 John Wiley & Sons, Ltd.     

Distribution of strong earthquake input energy in tall buildings equipped with damped outriggers

The seismic design of optimal damped outrigger structures relies on the assumption that most of the input energy will be absorbed by the dampers, whilst the rest of the structure remains elastic. When subjected to strong earthquakes, nevertheless, the building structure may exhibit plastic hinges before the dampers begin to work. In order to determine to which extent the use of viscously damped outriggers would avoid damage, both the host structure's hysteretic behaviour and the dampers' performance need to be evaluated in parallel. This article provides a parametric study on the factors that influence the distribution of seismic energy in tall buildings equipped with damped outriggers: First, the influence of outrigger's location, damping coefficients, and rigidity ratios core‐to‐outrigger and core‐to‐column in the seismic performance of a 60‐story building with conventional and with damped outriggers is studied. In parallel, nonlinear behaviour of the outrigger with and without viscous dampers is examined under small, moderate, strong, and severe long‐period earthquakes to assess the hysteretic energy distribution through the core and outriggers. The results show that, as the ground motion becomes stronger, viscous dampers effectively reduce the potential of damage in the structure if compared to conventional outriggers. However, the use of dampers cannot entirely prevent damage under critical excitations.     

Optimal vertical configuration of combined energy dissipation outriggers

The damped outrigger system emerged as an improvement of the conventional outriggers with the aim to provide supplemental damping and to contribute to the vibration control in super tall buildings where this system is usually applied. In addition to viscous dampers (VDs), buckling‐restrained braces (BRBs) have also been employed as energy dissipating members in outriggers. Nevertheless, the combined use of outriggers with VDs and BRBs in the same structure has not yet been studied. Such combination can contribute to achieve an effective multiperformance design of super tall buildings. This paper presents a study whose main objective was to determine the optimal vertical combination of two types of energy dissipation outriggers to control the seismic responses of a 9‐zone super tall model structure. Outriggers with VDs (OVDs) and outriggers with BRBs (OBRBs) were placed at the different zones of the structure considering all the possible combinations and in configurations of up to four outriggers. The effects of these combinations on the seismic performance of the structure were studied through parametric analysis and optimization methods. This form of the outrigger system is defined in this paper as combined energy dissipation outrigger system. The results indicate that when two energy dissipation outriggers are used, the combination of OBRB plus OVD shows superior seismic performance compared with other double‐outrigger configurations. In addition, the results show that the locations of OVDs and OBRBs play an important role in the structure behavior; it was found that it is more beneficial to place OBRBs above OVDs.     

A general solution for performance evaluation of a tall building with multiple damped and undamped outriggers

This paper presents a general solution for performance evaluation of a tall building with multiple damped and undamped outriggers. First, general rotational stiffness (GRS) is proposed to model an outrigger that consists of the stiffness of perimeter columns and an outrigger connection and the damping of dampers in an outrigger. By utilizing the dynamic stiffness method, the GRS can be represented by complex stiffness in an outrigger element. To analyze the dynamic characteristics of a tall building with multiple outriggers, a dynamic transcendental equation is obtained from the combination of the GRS and dynamic stiffness method. The structural responses can be calculated through the Fourier transform based on this equation. Moreover, the GRS can also be blended into a finite element (FE) model to generate an augmented state‐space equation for the analysis of the dynamic characteristics and structural responses. Applications to various outriggers are illustrated. In the numerical analysis, good agreements are found between the GRS and the FE that validates the proposed method, and the performances of various outrigger systems are evaluated parametrically. As the results of a tall building with multiple damped or undamped outriggers, the proposed method is capable of providing an optimally parametric design with respect to the position of outriggers, damping, and core‐to‐column and core‐to‐outrigger stiffness ratio. Copyright © 2015 John Wiley & Sons, Ltd.     

带加强层超高层结构受力性能研究及设计建议

在已有的简化理论分析结果基础上,对带加强层高层建筑结构进行空间建模,研究了倒三角形和均布侧向荷载作用下结构的顶点位移、框架柱内力与加强层数量、加强层伸臂与内筒线刚度比、外柱与内筒的刚度比的关系。通过一系列数值计算,分析了带加强层高层建筑结构的受力性能,通过侧移及内力与加强层位置、结构构件的刚度比等关系,得出了合理的刚度比取值范围及限值。研究结果可供实际工程参考。     

伸臂特性对框-筒结构中加强层力学性能的影响

本文根据伸臂结构的简化模型和伸臂与外框柱的变形协调条件,考虑伸臂的实际刚度,导出伸臂对核心墙的附加力矩,求得结构顶点侧移。对伸臂位置及刚度变化引起的侧移变化与内力突变进行了分析,结合工程分析结果对高层建筑加强层设计提出了一些参考意见。     

A simplified model for analysis of high‐rise buildings equipped with hysteresis damped outriggers

A simplified model is developed to estimate the seismic response of high‐rise buildings equipped with hysteresis damped outriggers. In the simplified model, the core tube is considered as a cantilever beam, and the effects of outriggers on the core tube are considered as concentrated moments. Modal decomposition method is adopted to obtain the seismic response of the simplified model. To investigate the accuracy and effectiveness of the simplified model, a high‐rise building with a height of 160 m was adopted as the example structure, and its response subjected to a ground motion was analyzed using the simplified model. A corresponding finite element model was built and analyzed by a finite element program called SAP2000 (Computers and Structures, Inc. Berkeley, California, United States). The analysis results obtained from the two models were compared. To consider the randomness of the ground motion, comparisons between the two models were further conducted using another 22 ground motions. It is found that the analysis results obtained from the simplified model agree well with those obtained from the finite element model, and the computation time used for the simplified model is almost negligible compared to that used for the finite element model. Such observations demonstrate that the simplified model is accurate and effective. Copyright © 2013 John Wiley & Sons, Ltd.     

An analytical model for high‐rise wall‐frame structures with outriggers

In this paper, the governing equations of wall‐frame structures with outriggers are formulated through the continuum approach and the whole structure is idealized as a shear–flexural cantilever with rotational springs. The effect of shear deformation and flexural deformation of the wall‐frame and outrigger trusses are considered and incorporated in the formulation of the governing equations. A displacement‐based one‐dimensional finite element model is developed to predict lateral drift of a wall‐frame with outriggers under horizontal loads. Numerical static results are obtained and compared with previously available results and the values obtained from the finite element package MIDAS. The proposed method is found to be simple and efficient, and provides reasonably accurate results in the early design stage of tall building structures. Copyright © 2007 John Wiley & Sons, Ltd.     

Reduction of vibration on a cantilever Timoshenko beam subjected to repeated sequence of excitation with magnetorheological outriggers

This paper deals with the statistical effects of an outrigger system on a cantilever beam under seismic excitation. The nonstationary random approach is employed to simulate seismic events. The Timoshenko beam approach is used to model the frame‐core tube linked at a point of its length by the damped outriggers, therefore are connected vertically two magnetorheological damper devices. The peak root‐mean‐square values of displacement responses is employed as a best measure effective to specify the optimal locations of outriggers according to different vibration modes. To evaluate the performance of the control system, the control algorithm based on Lyapunov stability theory is adopted to seek the input voltage leading to the reduction of vibration.     

Geometric nonlinear analysis of tall building structures with outriggers

In this paper, the geometric nonlinear behavior of wall‐frame tall building structures is analyzed. The governing equations of the wall‐frame systems with outrigger trusses are formulated through the continuum approach, and the whole structure is idealized as a shear‐flexural cantilever with rotational spring. The effect of shear and flexural deformation of the wall frame and outrigger trusses are considered and incorporated in the formulation of the governing equations. Geometric nonlinearity in the sense of von Karman is included in the formulation, and Newton–Raphson iterative method is employed to solve the nonlinear equations. A displacement‐based one‐dimensional nonlinear finite element model is developed. Numerical results for wall frame and mega‐column structures with outriggers are obtained and compared with the finite element package MIDAS. The proposed method is found to be simple and efficient, providing reasonably accurate results in early design stages of tall building structures. Copyright © 2011 John Wiley & Sons, Ltd.     

Analysis of a high‐rise steel structure with viscous damped outriggers

Damped outriggers for tall buildings draw increasingly attentions to engineers. With a shaking table test, two models of a high‐rise steel column‐tube structure are established, one with outriggers fixed to the core and hinged at the columns, whereas the other's cantilevering outriggers are connected to columns by viscous dampers. According to their dynamic properties, five earthquake waves are selected from the Ground Motion Database of Pacific Earthquake Engineering Research Center (PEER), and two artificial waves are generated by software SIMQKE_GR. Under various peak ground accelerations (PGAs), nonlinear time‐history analysis is applied to compare structural elastic seismic responses, including accelerations, inter‐story drifts, base shear force, damper's response and additional damping ratios. It is concluded that under minor earthquakes, accelerations, inter‐story drifts and base shear force of structure with damped outriggers are larger than or nearly equal to those of the one with fixed outriggers, and the viscous dampers hardly work. But as PGA increases, the contrary situation happens, and the effect of viscous dampers is enhanced as well. The additional damping ratio reaches around 4% under mega earthquakes. Copyright © 2013 John Wiley & Sons, Ltd.     

超高层建筑结构加强层耗能减震技术及连接节点设计研究

在框架-核心筒结构体系中,加强层可显著提高结构抗侧刚度、减小结构侧移,但会带来结构刚度、内力突变等不利影响。以某超高层建筑为工程背景,研究了黏滞阻尼器在伸臂桁架体系中的应用及在多遇地震和罕遇地震作用下的减震效果,研究了设置黏滞阻尼器的环带桁架在超高层建筑中的较优位置和减震效率。结果表明：黏滞阻尼器在伸臂桁架结构中的设置可以减小核心筒剪力墙的塑性损伤,减小结构的动力响应;设置黏滞阻尼器的环带桁架宜布置在层间相对速度大的位置,随超高层结构高度增加,阻尼器的减震效率降低。通过对伸臂桁架与外框柱、核心筒连接节点的设计及构造的分析,提出了连接节点的设计建议。     

昆明江东和谐广场超高层建筑结构抗震设计

昆明江东和谐广场项目B,D座超高层建筑为两栋平面基本对称的双子塔,采用带加强层的框架-核心筒混合结构体系,外围框架柱采用矩形钢管混凝土柱。介绍了该工程结构选型、抗震性能目标、各阶段抗震设计分析方法以及结构构件设计,重点阐述了核心筒剪力墙、外围框架和加强层的设计等关键问题处理和超限应对措施,并对高烈度区超高层建筑抗震设计进行深入探讨。     

上海白玉兰广场超高层混合结构设计

上海白玉兰广场办公塔楼大屋面高度300m,总高320m,采用了框架-核心筒-刚臂结构体系。型钢混凝土柱和钢梁组成混合结构框架,钢筋混凝土剪力墙围成核心筒,伸臂桁架和环带桁架形成的加强层作为刚臂连接外周框架和核心筒。采用了直径1.0m、长61m的桩底后注浆钻孔灌注桩,以及厚度为4.3m的基础底板。对结构设计性能指标和结构总体计算结果进行了介绍,并且对于外框和内筒竖向变形差异分析及处理、加强层设计、弹塑性分析等结构设计中的特殊问题进行了描述。     

Integrated multi‐type sensor placement and response reconstruction method for high‐rise buildings under unknown seismic loading

Structural health monitoring system has been implemented on high‐rise buildings to provide real‐time measurement of structural responses for evaluating their serviceability, safety, and sustainability. However, because of the complex structural configuration of a high‐rise building and the limited number of sensors installed in the building, the complete evaluation of structural performance of the building in terms of the information directly recorded by a structural health monitoring system is almost impossible. This is particularly true when seismic‐induced ground motion is unknown. This paper thus proposes an integrated method that enables the optimal placement of multi‐type sensors on a high‐rise building on one hand and the reconstruction of structural responses and excitations using the information from the optimally located sensors on the other hand. The structural responses measured from multi‐type sensors are fused to estimate the full state of the building in the modal coordinates using Kalman filters, from which the structural responses at unmeasured locations and the seismic‐induced ground motion can be reconstructed. The optimal multi‐type sensor placement is simultaneously achieved by minimizing the overall estimation errors of structural responses at the locations of interest to a desired target level. A numerical study using a simplified finite element model of a high‐rise building is performed to illustrate the effectiveness and accuracy of the proposed method. The numerical results show that by using 3 types of sensors (inclinometers, Global Positioning System, and accelerometers), the proposed method offers an effective way to design a multi‐type sensor system, and the multi‐type sensors at their optimal locations can produce sufficient information on the response and excitation reconstruction.     

带加强层框架-核心筒结构的静力弹塑性分析

高层框架-核心筒结构为提高抗侧刚度、降低剪力滞后效应,常设置伸臂与外围圈梁构成水平加强层.以模拟框架考虑核心筒的弹塑性性能,运用空间有限元程序对某带加强层框架-核心筒结构进行了静力弹塑性分析,考察了结构的抗侧刚度变化、屈服机制、出铰顺序等,得到若干具有工程设计参考价值的结论.     

Heights and locations of artificial structures in viewshed calculation: How close is close enough?

Viewshed calculation can play an important role in urban and natural resource planning. However, difficulties exist in incorporating built structures in viewshed computation. These features are rarely reflected in available elevation maps and adding them can be complicated as their locations, shapes, and heights are often uncertain. This study examined the impact of generalizing building locations and heights on viewshed properties. We used a geographic information system and high resolution data to assess how viewsheds, generated with actual building footprints and heights, differ from viewsheds generated from generalized building locations and uniform heights. We measured differences among viewsheds created with different approaches in terms of area and landscape complexity. Viewsheds generated using uniform heights and actual footprints differed significantly from the most accurate viewsheds in their areal extents and in the areas of some land use classes. Viewsheds produced using estimated locations combined with both realistic and uniform heights differed significantly from viewsheds created with accurate data in their areal extents and areas most land use types. Viewsheds produced using estimated locations also differed significantly from more accurate viewsheds in both complexity metrics assessed. Viewsheds produced using accurate locations and uniform heights differed significantly in one complexity metric, richness, but not in a second, diversity. Therefore, it may be feasible to generalize building heights when diversity and the areas of some specific land use classes are central to viewshed analysis, but generalizing building locations is less advisable. When viewshed areal extents are critical, location or height generalization may be ill-advised.     

天津响螺湾C-02地块项目主楼结构分析与设计

天津响螺湾C-02地块项目主楼地上54层,结构屋面高度约238m,结构体系为钢管混凝土框架-钢筋混凝土核心筒混合结构,在避难层和屋面设置了结构加强层。介绍了该项目的结构布置、性能目标、主要计算分析结果及抗震加强措施。结构设计满足超限要求,保证了结构的安全性和经济性,本工程的初步设计已通过超限审查。