Strength demand of dual‐purpose outrigger system for reducing lateral displacement and differential axial shortening in a tall building

Certain maximum lateral displacement (LAT) and differential axial shortening (DAS) values can lead to the deterioration of the serviceability of a structure. Previous studies indicated that an outrigger system can be used to control both the DAS and the LAT in a tall building. In order to enhance the applicability of the dual‐purpose outrigger system, the amount of stress developed on the outrigger due to the reductions of the LAT and DAS should be determined. Therefore, in this study, the stresses due to the LAT and DAS were analyzed in terms of the reduction ratio of the LAT and DAS, and the absolute sum of stresses, which was the strength demand of the outrigger, was evaluated as well. To identify the parameters affecting the additional stress of the outrigger, analytic equations were proposed to predict the additional shear force acting on the outrigger due to DAS reduction. A finite‐element analysis was performed to quantitatively identify the reduction ratio of the LAT and DAS as well as the resulting stress by changing four parameters: the stiffness, location, number, and connection time of outriggers. The results demonstrated that the stress of the dual‐purpose outrigger can be minimized by adjusting the design parameters.     

A comparison study of conventional construction methods and outrigger damper system for the compensation of differential column shortening in high-rise buildings

The outrigger and belt truss system is commonly used as one of the structural systems to effectively control the excessive drift due to lateral load and minimize the risk of structural and non-structural damage. However, this prominent structural system has a demerit of excessive stressing to structural and nonstructural members during construction due to differential column shortening. In this paper, several potential construction methods managing the outrigger to perimeter column joints experiencing differential column shortening are discussed. These methods include fixed joint without any adjustment, delayed joint, delayed joint with shim plate adjustment, and outrigger damper (or lock-up-device) installed joint. Based on our research through computer analysis, large scale laboratory test, shake table test and real installation of the apparatus to a high-rise project, the building with outrigger damper or lock-up-device system has many advantages in terms of building performance, construction convenience, quality control and cost reduction.     

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.     

An estimate on in‐construction differential settlement of super high‐rise frame core–tube buildings

To physically identify the mechanisms behind the development of in‐construction settlement of super high‐rise frame core–tube buildings, a simplified approach is developed by the full understanding about the typical structural layouts, specific construction feature, and load transfer path of those buildings as well as time‐dependent effects. With the reference to several typical structural layouts, a simplified one‐bay multistory model is developed that consists of two overall vertical components and horizontal components representing the exterior columns, core tubes, and beams (or mega trusses), respectively, in those super high‐rise buildings. Based on this model, a simplified approach with a so‐called “global–local” strategy is proposed to account for the difference in the settlement of the corner columns and side columns. The leading construction and final screwing at the rigid connections between beams (or trusses) and exterior columns, which are commonly implemented during the construction of those buildings, are seriously addressed in the simplified approach, as well as strengthened floors and time‐dependent effects. The applicability and accuracy of the proposed approach is demonstrated by a 128‐story 606‐m‐level super high‐rise frame core–tube building. The proposed simplified approach can be helpful for the development of preliminary construction schemes and the control strategy for differential settlement.     

Time‐dependent analysis of steel‐reinforced concrete structures

The time‐dependent behavior is a major consideration in the design and construction of tall buildings, especially in concrete and composite structural systems. To make an analysis of long‐term effect of steel‐reinforced concrete structures, the method of using master–slave constraint to deduce substructure element model of composite members was introduced, and the problem of co‐work between steel and concrete was solved. The creep calculation method of combined Age‐adjusted Effective Modulus Method (AEMM) and finite element method was adopted. Steel Reinforced Concrete Construction Modeling (SRCCM), a calculation program based on Visual C++ and ObjectARX, was developed for simulating the construction process of high‐rise composite structures. The use of the method is illustrated through one computation example of Shanghai Center Tower, which is a super high‐rise steel‐reinforced concrete structures. The method provides valuable information about time effects that may be used in designing new structures or in diagnosis existing structures. The results also indicate that the vertical shortening of Shanghai Center Tower between column and core‐tube is significant. Such differential length changes should be compensated during the construction process of high‐rise composite structures. Copyright © 2013 John Wiley & Sons, Ltd.     

单层导洞暗挖车站桩基差异沉降对结构内力影响分析

为研究单层导洞暗挖车站桩基差异沉降对结构内力的影响,以北京地铁16号线万泉河桥站工程为背景,通过建立车站平面有限元模型,分析桩基差异沉降加载方式和不同施工工况下桩基差异沉降值对车站结构内力影响.研究表明:两种不同的桩基差异沉降加载方式对结构内力影响差别不大,随着桩基差异沉降值的增加,车站结构内力不断增大.桩基差异沉降对...     

超高层建筑结构施工模拟技术最新进展与实践

施工顺序对结构的内力有明显影响,超高层建筑应采用结构逐层或分区激活的方式模拟实际施工过程。对于特殊的结构形式,需要正确选择各阶段激活的范围。通过合理调整施工顺序,得到更为合理的受力形态,减小结构用钢量。框架-延性墙板体系具有较大的侧向刚度与优良的抗震性能,严格控制其墙板的安装顺序对其实现抗震性能非常关键。收缩徐变对超高层建筑混凝土构件的竖向压缩变形量影响显著,各竖向构件的变形差异将引起水平构件附加内力,影响结构的安全性与正常使用,需要采取相应的设计与施工措施。温度作用对超高层建筑结构变形与内力的影响不能忽略。提出最大正、负温差的确定方法。应采取措施减小温度作用的不利影响,严格控制重要的温度敏感构件的合龙温度。基础不均匀沉降与超高层建筑的安全性关系密切,现阶段通过上部结构与地基基础共同工作模型准确预计基础沉降值尚难以实现,还需要通过设置施工后浇带、敏感构件滞后安装等方式尽量减小差异沉降的影响。     

Shear wall with outrigger trusses on wall and column foundations

A graphical method of analysis is presented for preliminary design of outrigger truss‐braced high‐rise shear wall structures with non‐fixed foundation conditions subject to horizontal loading. The method requires the calculation of six structural parameters: bending stiffness for the shear wall, bending and racking shear stiffnesses for the outrigger, an overall bending stiffness contribution from the exterior columns, and rotational stiffnesses for the shear wall and column foundations. The method of analysis employs a simple procedure for obtaining the optimum location of the outrigger up the height of the structure and a rapid assessment of the influence of the individual structural elements on the lateral deflections and bending moments of the high‐rise structure. It is concluded that all six stiffnesses should be included in the preliminary analysis of a proposed tall building structure as the optimum location of the outrigger as well as the reductions in horizontal deformations and internal forces in the structure can be significantly influenced by all the structural components. Copyright © 2004 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.     

Seismic design of outrigger systems using equivalent energy design procedure

An outrigger system is an effective structural scheme that is commonly used in high‐rise construction to increase the stiffness of concrete core walls and to reduce the moment demand within the walls. Despite the on‐going use of outrigger systems around the world, a formal seismic design procedure is yet available. This paper presents an equivalent energy design procedure (EEDP) to design outrigger systems for seismic applications. Three prototype outrigger‐wall buildings of various heights are designed for Vancouver, Canada. Detailed finite element models are developed to assess the seismic performance of the prototype buildings and to assess the safety using the FEMA P695 methodology. The result shows that EEDP is an efficient method to design outrigger systems which results in structures that can achieve sufficient margin of safety against collapse and satisfy multiple performance objectives at different seismic hazard levels.     

软黏土地基沉降的时变效应对超高层建筑结构内力的影响

软黏土地基沉降具有时变性,其规律被广泛认知。随着超高层建筑的大量兴建,工程师对超高层建筑与地基基础共同作用问题越来越重视。从地基沉降的时变性出发,综合考虑地基沉降的时变效应与地基-基础-上部结构共同作用的耦合问题,以时间切片的形式进行共同作用分析,提出了考虑地基沉降时变效应的共同作用计算方法,经初步分析得到地基沉降的时变效应对超高层建筑结构关键构件内力的影响。对软土地基上高500 m的超高层结构的分析结果表明,地基沉降的时变效应对上部结构的影响仅限于中低层区;其对巨柱、核心筒轴力的影响较小,轴力最大增、减幅值仅约为5%,在工程实践中可以忽略不计;但其对伸臂构件的影响较大,尤其是斜腹杆最为明显,其内力最大增幅可达200%,在工程实践中应给予重视。     

桩筏基础在竖向荷载作用下的时间效应

大量桩筏基础下存在较厚的饱和软弱下卧层 ,其变形和内力的研究不仅涉及到筏板、桩和土三者之间的相互作用 ,而且还跟时间有很大的关系。在建筑物施工和使用期间 ,地基变形逐步发展 ,基础的刚度不断变化 ,两者之间产生相互影响。地基的差异沉降还引起筏板及上部结构内力的变化。本文首次研究了存在软弱下卧层的桩筏体系的工作性状随时间变化规律 ,发现桩筏基础筏板内力、变形及桩顶反力受时间的影响较为显著     

Simplified column shortening analysis of a multi‐storey reinforced concrete frame

An improved column shortening analysis method which can be used at the design stage of a tall building has been proposed. The proposed analysis method considers construction sequences, the restraining effect of horizontal members, as well as creep and shrinkage. The whole analysis period is divided into two phases: before completion and after completion, and correction factors are applied only to the before‐completion phase to consider the gradual nature of construction sequences. Age‐adjusted effective moduli of the horizontal members considering the long‐term behaviour of the members are used for more exact internal forces. Column shortenings of a 70‐storey reinforced concrete frame–shear wall building were investigated as a numerical example. It is shown that the proposed analysis method can be used effectively to evaluate the effects of the differential column shortening to the horizontal members at the design stage. Copyright © 2010 John Wiley & Sons, Ltd.     

Seismic assessment of RC core‐wall building capable of three plastic hinges with outrigger

In a core‐wall structure with buckling restrained braces (BRB) outrigger, locations of the plastic hinges are influenced by the outrigger action. Therefore, the designer should consider the issue and use suitable details in the plastic hinge area. The essential questions that arise here are the plastic hinge location and the design moment demand used for design of this kind of structure. In this paper, responses of the core‐wall buildings with BRB outrigger designed by using the traditional response spectrum analysis procedure are assessed by implementing the nonlinear time history analysis. The result demonstrates that the plasticity can extend over anywhere within the core‐walls specially, at the base and above or below the outrigger levels. Formation of three plastic hinges in the core‐wall is recognized suitable for the system. To control the plasticity extension in the core‐wall, it is recommended that a new modal combination method be applied to calculate the moment strength of the three plastic hinges over the height. A capacity design concept is used to design other regions of the core‐wall where the plasticity does not extend to. The proposed procedure improves behavior of the system by restricting the plasticity extension to the predefined plastic hinge regions. Copyright © 2016 John Wiley & Sons, Ltd.     

Seismic performance analysis of viscous damping outrigger in super high‐rise buildings

This paper introduces a seismic energy dissipation technology—viscous damping outrigger (VDO)—which is composed of outrigger truss and viscous damper. The viscous damper is set up vertically at the end of outrigger truss, which is an innovative and high‐efficiency arrangement. VDO can fully utilize the characteristic of structural lateral deformation of super high‐rise buildings to increase the efficiency of viscous dampers for enhancing structural security, improving seismic performance, and reducing construction expenditure. In this paper, working principle and seismic energy dissipating mechanism of VDO are explained firstly. Then, the influence of viscous damper parameters on energy dissipation efficiency is studied. Next, the optimal position of VDO in a super high‐rise building is analyzed in detail. Lastly, the application of VDO in structural seismic design of a super high‐rise building in China will be clearly verified based on their feasibility, economy, and safety.     

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.     

A comparative case study on seismic design of tall RC frame‐core‐tube structures in China and USA

To evaluate the major differences between the Chinese and the United States (US) seismic design codes from a structural system viewpoint, a comparative case study is conducted on a tall frame‐core‐tube building, a typical type of reinforced concrete system widely constructed in both countries. The building, originally designed using the US seismic design code, is firstly redesigned according to the Chinese seismic design code based on the information provided by the Pacific Earthquake Engineering Research Center. Secondly, the member dimensions, the dynamic characteristics, the seismic design forces and the material consumptions of the two designs are compared in some detail. Subsequently, nonlinear finite element models of both designs are established to evaluate their seismic performances under different earthquake intensities. Results indicate that the seismic design forces determined by the Chinese response spectrum are larger than those determined by the US spectrum at the same seismic hazard level. In addition, the upper‐bound restriction for the inter‐story drift ratio is more rigorously specified by the Chinese code. These two aspects have led to a higher level of material consumption for a structure designed by the Chinese code. Despite of the above discussions, the two designs yield roughly similar structural performances under earthquakes. Copyright © 2015 John Wiley & Sons, Ltd.     

盾构隧道纵向沉降模式及其结构响应

软弱地基的不均匀沉降导致隧道结构产生附加结构变形与次生内力,根据大量工程实测资料,总结了包含盾构隧道施工与长期使用阶段在内的隧道地基沉降的4种典型模式．然后基于弹性地基理论,分别推导并给出了这四种地基沉降模式下隧道结构的纵向变形及结构内力解析表达式,探讨了不同地基变形模式下隧道结构的响应规律,这为隧道的纵向设计及考虑纵向剪切传递影响的横向设计研究奠定了基础。     

Einsparpotentiale bei Tragkonstruktionen von Offshore‐Windenergieanlagen

Savings potential for support structures of offshore wind turbines. Due to the high ratio of dynamic loads from wind and wave forces on offshore wind turbines, the fatigue design analysis proves to be the determining factor for the dimensioning of support structures. As a result, the current design practice is limited, particu‐larly with regard to the economic benefits of employing high strength steels. Especially from the aspect of mass production, however, the economic optimization of the components is a sub‐stantial economic advantage for the companies. This paper presents different options for savings in the design and assessment of offshore‐foundation structures and provides the example of a transition piece for a jacket foundation structure. Savings potential is realized through optimal construction design, directionally dependent load determination, a refined methodology of analysis, as well as through modern methods of post weld treatment.     

Three‐dimensional computer‐aided finite element method retrofitting modeling and non‐destructive testing techniques for the assessment of actual existing high‐rise fire‐damaged reinforced concrete building

Concrete is generally fire resistant. A fire in a concrete structure rarely results in a serious damage as to require substantial demolition. But, loss of the utility of a building could result in serious financial consequences for the owner, which calls for immediate reinstatement. To work out proper and efficient repair strategy, however, would require a thorough investigation of the effect of fire on the structural properties of the concrete and steel; the significance which any permanent change in material characteristics may have on the future structural performance of the member; the feasibility of repairs to compensate of any unacceptable reduction in structural performance, durability, and so on; and the influence which fire exposure of individual member may have on the performance of the entire structure. These all said tasks are dependent on the complete analysis of the fire‐damaged building. Without it, no repair works estimation, extent of repair and kind of repair can be carried out for the fire‐damaged buildings. Therefore, the impeccable analysis and design is of utmost importance for repair of such buildings after preliminary investigation of the extent of fire damages to the concrete structural members. This forms the basis of this research study, which aims at detailed analysis and design of the actual existing high‐rise fire‐damaged buildings for fire retrofitting and assessment of fire damages by non‐destructive techniques. Fire damages in buildings due to explosion, accidents or by some other reasons cause severe structural damages. The structural integrity of existing buildings is now a burning issue. Analytical, theoretical and design‐cum‐construction techniques are constantly being reviewed by government agencies and engineering consultants. Therefore, researchers are delving into this matter to find the best retrofitting techniques for fire‐damaged buildings. This paper is an outcome of such detailed research studies. It covers the actual case study of existing buildings, review of existing knowledge for fire damages and their mitigation and protective design technologies, and analytical and computational techniques, which have limited research data. In this study, Extended 3D Analysis of Building Systems (ETABS) is used as software for fire retrofitting analysis, and UBC‐97 is used as a code for the fire analysis and design. The ETABS building model is verified by manual calculations as well. Copyright © 2011 John Wiley & Sons, Ltd.