Energy dissipation and performance assessment of double damped outriggers in tall buildings under strong earthquakes

The use of a single set of outriggers equipped with oil viscous dampers increases the damping ratio of tall buildings in about 6–10%, depending on the loading conditions. However, could this ratio be further increased by the addition of another set of outriggers? Should this additional set include dampers too? To answer these questions, several double damped outrigger configurations for tall buildings are investigated and compared with an optimally designed single damped outrigger, located at elevation 0.7 of the total building's height (h). Using free vibration, double outrigger configurations increasing damping up to a ratio equal to the single‐based optimal are identified. Next, selected configurations are subjected to several levels of eight ground motions to compare their capability for avoiding damage under critical excitations. Last, a simplified economic analysis highlights the advantages of each optimal configuration in terms of cost savings. The results show that, within the boundaries of this study, combining a damped outrigger at 0.5h with a conventional outrigger at 0.7h is more effective in reducing hysteretic energy ratios and economically viable if compared with a single damped outrigger solution. Moreover, double damped outrigger configurations for tall buildings exhibit broader display of optimal combinations, which offer flexibility of design to the high‐rise architecture.     

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.     

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.     

Optimal parameters for tall buildings with a single viscously damped outrigger considering earthquake and wind loads

Tall buildings suffer from low inherent damping and high flexibility. Therefore, a core-outrigger system is often used to stiffen such buildings. A modified form, known as the damped outrigger system, wherein vertically oriented dampers are installed between outriggers and perimeter columns, has been recently developed to supplement the damping. This paper studies the efficacy of a viscously damped outrigger system through dynamic analysis of a 60-story tall building subjected to nonconcurrent earthquake and wind excitations. Two ground motion sets (100 accelerograms) are used for the former and wind tunnel test data for the latter. Effects of three building parameters, namely, (i) the core-to-column stiffness ratio, (ii) the outrigger location, and (iii) the damper size, on the dynamic characteristics and seismic and wind responses are evaluated. Effects of damper nonlinearity on seismic and wind responses are also investigated considering energy-equivalent nonlinear viscous dampers. Finally, the optimum values of these parameters are determined. For example, the optimum outrigger location is found to be between $0.6H$ to $0.9H$, where $H$ is the height of the building. The results also show that the damped outrigger system significantly outperforms the conventional one for seismic excitation, and it is very effective in reducing the wind-induced floor accelerations, provided the parameters are chosen appropriately.     

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.     

带伸臂超高层结构最优伸臂道数及位置确定的灵敏度向量法

以最大层间位移角为优化目标,提出一种简单有效的向量积算法,可以快速确定最优的伸臂桁架设置数目及位置。以上海中心大厦为例,给出了该算法的应用方法及过程,并结合分析结果对带伸臂超高层结构的最优伸臂道数及位置的设置规律进行了分析。对于典型的100层以上的超高层建筑,向量积算法的效率比常规的穷举法提高约28倍。分析表明,最优的伸臂桁架设置方案与桁架设置的数目和位置均有关系,且伸臂桁架设置方案的最优性并非随着伸臂桁架数目的增加而增加。     

基于振动台试验的超高层结构伸臂消能体系抗倾覆性能研究

本研究通过对某超高层结构模型进行模拟地震振动台试验,考察核心筒、外围框架与伸臂结构组成的抗侧力体系在地震作用下的整体抗倾覆性能,重点分析在伸臂结构设置黏滞阻尼器的消能减震策略对结构底部弯矩的控制效果,为该类超高层结构体系减震研究提供参考。     

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.     

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。     

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.     

群体高层建筑风致干扰效应研究进展

在高层建筑抗风设计中,正确地评估邻近建筑对风荷载的影响具有重要的理论和实用价值。从干扰机理、基底荷载干扰以及风压干扰3个方面总结与评述了国内外风致干扰效应的研究进展,列举了各国风荷载规范对干扰效应的条文规定;结合作者所在研究团队近十多年来进行的群体高层建筑的研究成果,对GB 50009-2012《建筑结构荷载规范》的风致干扰条文进行了补充说明,重点介绍了群体建筑气动干扰的量化方法,并强调了干扰效应的适用条件为折算风速不大于7;根据前期研究存在的问题和实际工程需求,建议进一步开展对群体建筑干扰机理、结构顶部峰值加速度、扭转干扰响应以及不同方向荷载相关性等方面的系统性研究。     

Multiperformance optimization design of a hybrid vibration mitigation system for super high‐rise buildings to improve earthquake resistance

A structure must meet many performance requirements to survive an earthquake. For a super high‐rise structure, the dominant control performance metric is stiffness when considering earthquake resistance because the lateral displacement of the structure often does not meet the requirements of the code even if the structure meets strength requirements. For moderate and major earthquakes, stiffness and strength play a leading role jointly. Viscous damper (VD) and buckling restraint brace (BRB) are damping devices that are commonly used in modern engineering. The efficiencies of these devices are different for different situations, and combining them can yield improved structural vibration mitigation. In this study, the performances of VD and BRB are summarized. A kind of virtual VD model with an additional damping ratio is proposed on the basis of which a VD priority placement analysis method is developed, and an optimal design is proposed. A detailed analysis of various stress states of a BRB is also performed, and a BRB arrangement method based on brace stress level analysis is proposed. The two kinds of vibration damping equipment are combined in the structure, and a practical design method for a hybrid vibration damping system is proposed. The accuracy of the proposed method is verified by considering a 10‐story plane frame. Finally, a hybrid vibration mitigation design for different objective damping ratios is performed for a super tall building project, and the design results are compared. The analysis results show that a VD can effectively increase structural damping and reduce the seismic response of the structure. A BRB is used to replace supports that experience high stress and reduce their section size, thereby reducing costs. Therefore, the proposed hybrid vibration damping structure is cost effective while providing good energy dissipation and is thus promising for engineering applications.     

复杂高层建筑抗震与消能减震研究进展

复杂高层建筑的震害在近来的历次地震中都有发生,其抗震分析和设计难度较大,提高其抗震性能是当前建筑抗震的难点之一。通过对近10年来国内在复杂高层建筑抗震方面的研究进行回顾和总结,重点介绍了组合剪力墙及筒体结构、钢管混凝土结构、结构模型振动台试验和三种消能减震方法。提出了采用新型高效的结构体系及高性能抗震部件或消能减震新技术改善复杂高层建筑抗震性能。这些研究工作与工程实践紧密结合,大部分研究成果已在实际工程中成功应用。图18参28     

Torsional coupling effects in the earthquake response of asymmetric buildings

This paper presents a detailed parametric study of the coupled lateral and torsional response of a partially symmetric single storey building model subjected to both steady state and earthquake base loadings. It is shown that the qualitative effects of the controlling parameters on the maximum translational and torsional responses of the coupled system are not affected by the nature of the loading. The maximum lateral edge displacement of the building arising from the combined response effects is investigated. The related lateral shear forces in vertical resisting elements located on the periphery of the structure may be significantly increased in comparison with the corresponding values for a symmetric building. It is concluded that for particular ranges of the key parameters defining the structural system, typical of the properties of many actual buildings, torsional coupling induces a significant amplification of earthquake forces which should be accounted for in their design.     

超高层建筑结构优化过程中的环境成本计算

近年来中国大陆掀起了超高层建筑的兴建热潮。超高层建筑体量巨大,其碳排放和能源消耗对环境有显著影响。在评估和优化超高层建筑的全生命周期环境成本时,提出了一个全新的全生命周期模型。新模型有两大特征：首先,同时考虑了建筑材料的空间分布与时间特征;其次,把单尺度生命周期概念拓展到多尺度生命周期概念,以从更多角度来研究碳排放情况。建立了一个基准超高层建筑模型来阐释对新模型的应用。根据初步研究结果,应用新方法可以选择出更优化的结构设计方法,以最大程度减少碳排放量。     

高层建筑加压送风系统影响因素的实验研究

通过现场实验研究，讨论风机设置于建筑上部的多点加压送风系统的设计，通过数值拟合的方法得出送风管道中的风速分布，风速与加压风机的流量、送风管道的截面积以厦管道的高度有关。在实际情况下，研究影响高层建筑加压送风系统的各种因素有着较为重要的意义。     

设置黏滞阻尼器的悬挂减振结构振动台试验研究

通过对设置黏滞流体阻尼器的悬挂结构进行地震模拟振动台试验,分析了主结构与悬挂楼面的质量比、连接方式以及阻尼器分布对悬挂结构模型的频率、阻尼比和结构响应的影响。试验结果表明：与刚性杆连接的常规悬挂结构相比,采用阻尼器连接主结构和悬挂楼面,可改变结构频率,提高结构振型阻尼比,且模型前3阶振型主要表现为悬挂楼面剪切变形;悬挂减振结构主结构的位移峰值响应小于常规悬挂结构,略小于无连接的自由悬挂结构;当悬挂楼段质量较大时,减振效果更好;与自由悬挂结构相比,阻尼器连接的悬挂减振结构能较好地抑制悬挂楼面相对于主结构的位移和悬挂楼面的层间位移;当悬挂楼面侧向刚度较小时,阻尼器均匀布置比集中布置能更好地控制悬挂楼面的相对位移。     

Pressure transient suppression in drainage systems of tall buildings

ABSTRACT

The suppression of pressure transients in building drainage systems is essential for reducing cross-contamination by the spread of pathogens. The topic is now much better understood due to work following the invention of the first drainage-specific positive-pressure transient-attenuation device in the year 2000. The present research addresses the attenuation of much larger problematic air-pressure transients found in tall buildings. The development of a new technique is described for the attenuation of positive air pressure transients of approximately 2000?mm water gauge (wg) (20?kPa) for which there is currently no means to alleviate. The performance of the new technique was validated by numerical simulation and full-scale test-rig experiments. The full-scale test rig represented a 44-storey building with a 150?mm main drainage stack. The pressure wave generator applied a 2000?mm wg pressure transient from a large accumulator compressor delivering 270 litres of air at 10 bar pressure. This resulted in a capacity of 2700 litres of air at atmospheric pressure delivered into the system within 0.2?s. Results show that a prototype device using the new technique is capable of reducing the applied pressure transient by 88%, rendering it harmless and returning the system to normal operation in a matter of seconds.     

高层建筑中箱基和上部结构共同作用下的计算和调整沉降方案

笔者2次指出国内外技术规程中建议的箱基与上部结构共同作用下的计算是错误的,并建议新的计算。为了从理论上解决箱基渗漏问题,曾提出“反盆式沉降方案”,现改为“调整沉降方案”,并介绍了工程实例。     

Effectiveness of passive response control devices in buildings under earthquake and wind during design life

The effectiveness of passive vibration control devices used to retrofit multi-storied steel buildings during their design life is investigated under the dynamic forces induced by earthquake and wind. The passive vibration control devices include steel bracing, viscous and viscoelastic dampers. The buildings without and with the retrofitting devices are modelled as multi-degree of freedom (M-DOF) systems, with inertial masses lumped at each floor level. The governing differential equations of motion for the uncontrolled and controlled buildings are solved using Newmark’s time marching scheme. The obtained dynamic responses for the buildings exposed to the earthquake- and wind-induced forces are subsequently compared. It is concluded that upon retrofitting, the modified dynamic properties, such as modal frequencies and damping ratio play an active role to attract forces during the two hazards, which in turn influences the response reduction achieved. It may be worth noting that the buildings retrofitted for earthquake tend to attract more forces under wind load and vice versa. Therefore, a retrofit strategy providing beneficial effects against a particular hazard may prove to be catastrophic for the other, which underlines the need for careful selection of the retrofit solution and design for a structure considering such multi-hazard scenario.