Time-frequency analysis of typhoon effects on a 79-storey tall building

Di Wang Tower located in Shenzhen, PR China, has a height of approximately 325 m and is a 79-storey tall building. This paper presents selected results of full-scale measurements of typhoon effects on Di Wang Tower. Wind speed, wind direction, wind-induced acceleration and displacement responses were simultaneously and continuously measured from the super tall building with anemometers, accelerometers and global position system (GPS) during a typhoon. The advanced data analysis method called Hilbert-Huang transform (HHT) was adopted in this study to analyze the non-stationary characteristics of wind speed and wind-induced responses of this building under typhoon condition. By using the empirical mode decomposition (EMD) method, the measured data were decomposed into several inherent intrinsic mode functions (IMFs). The probability density and power spectral density of fluctuating wind speed were obtained by traditional methods and were further analyzed by considering time-varying mean values of the measured data via the EMD method. The wind-induced responses with non-stationary features were studied by applying the HHT to each IMF for obtaining their instantaneous frequency and Hilbert-Huang composite spectrum. Meanwhile, the transient energy distributions of the wind-induced responses were analyzed in time-frequency domain, which were compared with the traditional power spectral densities obtained from the fast Fourier transform (FFT) method and those from the wavelet transform. Furthermore, the amplitude-dependent damping ratios were determined by combining the EMD and the random decrement technique (RDT) method. Through comprehensive analysis of the measured data, it was testified that the HHT method is a promising tool for the time-frequency analysis of random signal and can serve as a flexible and effective tool for analyzing field data of wind speed and wind-induced response with non-stationary features.     

Monitoring of structural modal parameters and dynamic responses of a 600m‐high skyscraper during a typhoon

This paper presents field measurement results of structural dynamic properties and wind‐induced responses of 600m‐high Ping‐An Finance Center in Shenzhen during the passage of Typhoon Haima. The field measurements included wind speed, wind direction, and structural acceleration responses during the typhoon. Analysis of the field measurements is carried out to investigate the wind‐induced structural vibrations and dynamic properties of the skyscraper under typhoon condition. In the analysis, natural frequencies and damping ratios of Ping‐An Finance Center are estimated using Peak‐Picking method, half‐power bandwidth method in frequency domain, and random decrement technique in time domain, respectively. Two band‐pass filtering methods, namely, elliptical filtering method and Kaiser‐window FIR filter, are adopted to deal with the measured acceleration signals. Consequently, the modal parameters identified with the Peak‐Picking, half‐power bandwidth, and random decrement technique methods are presented and discussed in detail. In addition, the probabilistic characteristics of the recorded acceleration responses are analyzed using the generalized extreme value distribution, and then the serviceability of the skyscraper during the typhoon is evaluated.     

Probabilistic assessment of vibration exceedance for a full‐scale tall building under typhoon conditions

Full‐scale wind and vibration measurements were conducted on a 270‐m tall building in Hong Kong. For the modal identification, a refined fast Bayesian fast Fourier transform method was newly developed by considering the exponential form of the modal wind force spectrum. Then, the modal parameters of the monitored building and their uncertainties were identified from the full‐scale vibration data under typhoon conditions by the proposed refined fast Bayesian fast Fourier transform method. For assessing the vibration exceedance of the monitored building under typhoon, a stochastic wind force field generation technique was developed by combining the spectral representation method and the computational fluid dynamics method. Wind‐induced vibration of the tall building under Typhoon Kammuri was reanalyzed with generated wind force time history data. Finally, a time‐domain Monte Carlo simulation framework was proposed by integrating the modal identification and the stochastic wind force field generation technique. In this framework, the Metropolis–Hastings sampling algorithm was adopted to estimate the vibration exceedance probability, which was defined through a limit state performance function associated with the ISO vibration assessment criteria.     

Field measurements of amplitude‐dependent damping in a 79‐storey tall building and its efects on the structural dynamic responses

This paper describes some results obtained from full‐scale measurements of wind effects on a super‐tall building, Di‐Wang Tower, located in Shenzhen, China. This tall building has 79‐storeys with a height of approximately 324 m. Field measurements including wind speed, wind direction and wind‐induced acceleration responses have been made. The amplitude‐dependent characteristics of damping are obtained by using the random decrement technique from the detailed analysis of the field acceleration measurements. The main objective of this paper is to present detailed investigations into the effects of nonlinear damping on the dynamic responses of the tall building subjected to various types of applied loads based on the measured amplitude‐dependent damping characteristics. The predicted dynamic responses of the building obtained by using the measured damping characteristics were compared with those computed by using constant damping parameters assumed by the structural designers. It is concluded from the investigations that knowledge of actual damping characteristics are very important in the accurate prediction of the dynamic responses of a tall building when the major harmonic components of the applied loads overlap with the lowest natural frequencies of the building. The design damping level for tall building structures currently used by structural engineering practitioners appears to be high and not conservative. Copyright © 2002 John Wiley & Sons, Ltd.     

Modal parameter identification of Tsing Ma suspension bridge under Typhoon Victor: EMD-HT method

This paper aims to identify the natural frequencies and modal damping ratios of the Tsing Ma suspension bridge during Typhoon Victor using the newly emerged empirical mode decomposition (EMD) method in conjunction with the Hilbert-transform (HT) technique. Stationary tests on the acceleration responses of the bridge recorded at different locations and in different directions during Typhoon Victor are first carried out to classify the recorded response data. Natural frequencies and modal damping ratios identified by the EMD-HT method are then compared with those obtained by the traditional fast Fourier transform (FFT)-based method. The modal parameters identified by the EMD-HT method from the bridge responses recorded at different locations are compared with each other to check their consistency. Furthermore, the variations of natural frequency and total modal damping ratio with vibration amplitude and mean wind speed are examined. The results demonstrated that the EMD-HT method is applicable to modal parameter identification of large civil structures under typhoons. The EMD-HT method and the FFT-based method produced almost the same natural frequencies but the FFT-based method gave higher modal damping ratios than the EMD-HT method in general.     

Wind effects on Shenzhen Zhuoyue Century Center: Field measurement and wind tunnel test

Field measurements of wind effects on Zhuoyue Century Center were conducted during 4 typhoon events in the recent 5 years, during which the field data such as wind speeds, wind directions, and acceleration responses were simultaneously and continuously measured. On the basis of field measured data, dynamic characteristics of this super‐tall building were determined by recently developed fast Bayesian fast Fourier transform method. Using full‐scale measurement data under 4 typhoons and breezy conditions for modal identification, one could observe a relatively wide scatter in the identified modal damping ratios, and the damping ratios do not appear to have an obvious nonlinear relationship with vibration amplitude. The average damping ratios of the first 2 modes were 0.70% and 0.73%, respectively. Serviceability of the super‐tall building under wind action was analyzed on the basis of the field measured response. Finally, the measured wind‐induced acceleration responses were further compared with those obtained from the wind tunnel test to evaluate the accuracy of the model test results.     

强台风作用下深圳卓越世纪中心的实测研究

超高层建筑的结构动力特性是影响结构风效应评估精度的重要因素,实测是获取实际结构动力特性参数的唯一方法并已有很多研究,但实测研究中出现较大振幅的情况仍极为少见。文章采用自主研发的无线加速度传感器,对高度280m的深圳卓越世纪中心北塔(ZCC)进行连续长期监测,得到10年来多次台风作用下ZCC结构顶部加速度响应时程信号。采用不同参数识别方法分别对ZCC在5次具有代表性的台风作用下的结构顶部加速度响应时程数据进行详细分析,并将台风“山竹”的实测结果和风洞试验的结果进行对比。结果显示：不同方法识别得到的结构模态频率一致性较好,模态阻尼比则存在一定差别;结构模态频率有随振幅增大而减少的趋势,顺风向的结构模态阻尼比随加速度的增大有增大的趋势,横风向的结构阻尼比则呈现较大的离散性,和加速度振幅的相关性不明显;现场实测得到的ZCC在台风“山竹”作用下的结构顶部峰值加速度和风洞试验结果具有较好的一致性,且在连续10年中测到的最大峰值加速度为23.91cm/s²,表明该建筑能够满足舒适度要求。     

环境风激励下的深圳平安金融中心模态参数识别

对高度600 m的超高层建筑——深圳平安金融中心在外界环境风激励下的风振响应进行了现场实测。通过安装在塔楼118层的2组加速度传感器测得结构的风致加速度响应,采用经验模态分解法（EMD）与随机减量技术（RDT）相结合的方法计算了结构的自振频率和阻尼比。建立了深圳平安金融中心三维有限元模型,通过有限元分析得出结构的自振频率,并与实测结果进行对比。结果表明:由EMD和RDT相结合的方法计算得出结构1阶横弯自振频率约为0.12 Hz,阻尼比为0.3%~0.6%;结构1阶扭转自振频率约为0.28 Hz,阻尼比为0.8%~1.0%;深圳平安金融中心实测结构自振频率和阻尼比与其他结构高度相似的超高层建筑实测结果相近,且实测结果和有限元分析结果吻合较好,验证了EMD和RDT结合方法分析超高层建筑模态参数的有效性;测试结果可以为超高层建筑设计和相关研究提供依据。     

Identification of damping ratio and its influences on wind‐ and earthquake‐induced effects for large cooling towers

Standard 5% damping ratio for high‐rise concrete structures is generally used for dynamic analysis under the action of wind and earthquakes in the existing cooling tower regulations and researches. But considering the unique configuration and material attributes of large cooling towers, the actual damping ratio must be far smaller than the recommended. However, only a few field measurements of damping ratio for large cooling towers have been conducted; neither are there thorough investigation into the qualitative and quantification of wind and seismic effects under different damping ratio. To fill this gap, field measurements of a large cooling tower standing 179 m in northwestern China was performed and acceleration vibration signals at representative positions of the tower under ambient excitation were obtained. The vibration signals were preprocessed combining random decrement technique and natural excitation technique. Three pattern recognition methods (auto‐regressive and moving mean model, Ibrahim time domain, and spare time domain (STD)) were applied to analyze the frequencies, damping ratios, and modes of vibration for the first 10 order modes. Following the line of thought of modal combination, the equivalent synthetic damping ratio was derived. Under 5 damping ratios (0.5%, 1%, 2%, 3%, and 5%), a comparative analysis on the dynamic responses of the cooling tower to wind and single seismic loading by using full transient method was performed. On this basis, the patterns of influence of damping ratio on wind‐induced vibration, wind vibration coefficient, and time history and extrema of seismic responses were extracted. Finally, different combinations of dead weight, wind, temperature in winter, sunshine duration, and seismic intensity and those of accidental seismic effects (8 working conditions) were considered, using equivalent synthetic damping ratio and standard damping ratio. Thus, the most unfavorable working conditions were identified under actual and standard damping ratios for the large cooling tower. Our research findings provide reference for determining the value of damping ratio in large cooling towers and deepening the understanding on the influence mechanism of damping ratio.     

Time–frequency analysis of structural dynamic characteristics of tall buildings

This study focuses on the correlations between the structural dynamic properties and the instantaneous response characteristics of a 492-m high building during a typhoon. An instantaneous analysis framework is established based on a combined usage of both linear-phase filtering and time–frequency techniques. This analysis framework can separate each modal response contribution without phase distortions. Random decrement technique is used to estimate the modal damping ratios. It is found that beating phenomenon widely exists in the separated modal response contributions, and the damping ratios correlate with the modulation of phase and amplitude within the beating closely. When the beating amplitude comes close to zero, the instantaneous frequency fluctuates evidently. The more intensive this fluctuation is, the larger the damping ratio becomes. An empirical model is presented to formulate the variations of damping ratio and natural frequency of this building with the fluctuation intensity of the instantaneous frequency.     

厦门沿海某超高层建筑结构风致振动动力特性研究

现场实测是获得结构风致振动动力特性参数的一种较为可靠的手段和方法。通过对厦门沿海某超高层建筑在台风登陆时进行现场原型实测,得到了该建筑结构的第10层、18层、23层、28层、33层和36层的加速度响应时程数据和固有频率及振型等结构的动力特性。根据实测加速度数据,利用随机减量法提取结构两方向的前3阶固有频率对应的阻尼比,结果表明：由于实测时台风风速较大,导致结构风致响应较为显著,因此结构两个方向第1阶阻尼比值在7%左右,明显大于另外两阶阻尼比;两方向第1阶阻尼比与加速度呈非线性关系,阻尼比随加速度的增大而增大。采用ANSYS软件建立该超高层建筑的3D有限元分析模型并进行模态分析,提取该模型的前3阶固有频率和振型,与实测结果进行对比分析,结果较为吻合,由此说明所建立的3D有限元分析模型正确可靠。     

地王大厦动力特性及大风时楼顶位移和加速度实测研究

本文介绍了深圳地王大厦的动力特性和在大风时楼顶位移和加速度的实测结果,并对实测结果进行了讨论.     

Performance Evaluation of TMD under Typhoon Using System Identification and Inverse Wind Load Estimation

Abstract: The typhoon behavior and performance of a tuned mass damper (TMD) are presented based on the system identification and the inverse modal wind load estimation. The TMD was installed on a 39‐story, 184.6‐m steel building located in Incheon, Korea with a monitoring system consisting of an anemometer, accelerometers, and internet‐based data logging system. On September 2, 2010, the building experienced the Kompasu Typhoon, in which the peak wind speed, measured by an anemometer installed on the roof floor, was 49.7 m/s. To analyze the behavior of the building during the typhoon, the dynamic properties of building and TMD are identified from the measured responses. The modal wind load is then inversely estimated from the TMD and building accelerations using a Kalman filter, and the vibration reduction performance of the TMD is evaluated. The analysis results show that the typhoon‐induced vibration was reduced significantly due to the installation of TMD.     

Field measurements of wind and structural responses of a 70‐storey tall building under typhoon conditions

This paper describes the results obtained from the full‐scale measurements of wind effects on a 70‐storey tall building in Hong Kong. The objective of the experiment is to measure wind action on and wind‐induced response of the tall building. Simultaneous and continuous data of wind speeds, wind directions and acceleration responses have been recorded at the top of the tall building since 1995. The field data presented in this paper were measured during the passage of four typhoons—Typhoon Kent (1995), Typhoon Ryan (1995), Typhoon Sibyl (1995) and Typhoon Sally (1996). The characteristics of the typhoon wind and the structural responses of the building are investigated. The serviceability of this tall building under typhoon conditions is discussed on the basis of the field measurements. Copyright © 2000 John Wiley & Sons, Ltd.     

Blind Modal Identification in Frequency Domain Using Independent Component Analysis for High Damping Structures with Classical Damping

Output‐only modal identification methods are practical for large‐scale engineering. Recently, independent component analysis (ICA) which is one of the most popular techniques of blind source separation (BSS) has been used for output‐only modal identification to directly separate the modal responses and mode shapes from vibration responses. However, this method is only accurate for undamped or lightly damped structures. To improve the performance of ICA for high damping structures, this article presents an extended ICA‐based method called ICA‐F, which establishes a BSS model in frequency domain. First, the basic idea of BSS and ICA applied in modal identification is introduced in detail. The free vibration responses and the correlation functions of ambient responses can be cast into the frequency‐domain BSS framework just by mapping the time history responses to frequency domain through fast Fourier transform (FFT). Then, an ICA‐based method in frequency domain called ICA‐F is proposed to accurately extract mode shapes and modal responses for both light and high damping structures. A simulated 3 degree of freedom mass‐spring system and a 4‐story simulated benchmark model developed by the IASC‐ASCE Task Group in Health Monitoring are employed to verify the effectiveness of the proposed method. The results show that the proposed method can perform accurate modal identification for both light and high damping structures. Finally, the IASC‐ASCE experimental benchmark structure is also utilized to illustrate the proposed method applied to practical structure.     

地王大厦结构设计若干问题

深圳地王大厦是一座高达368m,横向高宽比为8.78的超高层建筑,结构设计上遇到不少新的问题.该大厦结构系由日本新日铁株式会社设计部设计,作为该大厦的结构设计顾问,作者有机会与设计者就诸多重大设计技术问题进行了咨询与探讨.现就地王大厦风载的确定,结构抗风抗震设计,特别是怎样计算与控制结构在风和地震作用下顶点和层间位移等关键技术问题给予说明与探讨,最后简单介绍了大厦建成后进行监测和测试的初步结果.     

Modal Response‐Based Visual System Identification and Model Updating Methods for Building Structures

This article proposes a new system identification (SI) method using the modal responses obtained from the dynamic responses of a structure for estimating modal parameters. Since the proposed SI method visually extracts the mode shape of a structure through the plotting of modal responses based on measured data points, the complex calculation process for the correlation and the decomposition for vibration measurements required in SI methods can be avoided. Also, without dependence on configurations of SI methods inducing variations of modal parameters, mode shapes and modal damping ratios can be stably extracted through direct implementation of modal response. To verify the feasibility of the proposed method, the modal parameters of a shear frame were extracted from modal displacement data obtained from a vibration test, and the results were compared with those obtained from the existing frequency domain SI method. The proposed method introduces the maximum modal response ratio of each mode computed by modal displacement data, and from this, the contribution of each mode and each measured location to the overall structural response is indirectly evaluated. Moreover, this article proposes a model updating method establishing the error functions based on the differences between the analytical model and measurement for the natural frequencies and the modal responses reflecting both mode shape and modal contribution. The validity of the proposed method is verified through the response prediction and modal contributions of the models obtained from model updating based on dynamic displacement from a shaking table test for a shear‐type test frame.     

A Two‐Step Model Updating Algorithm for Parameter Identification of Linear Elastic Damped Structures

A Frequency Response Functions (FRFs)‐based two‐step algorithm to identify stiffness, mass, and viscous damping matrices is developed in this work. The proposed technique uses the difference between the experimentally recorded FRF and their analytical counterparts by minimizing the resultant error function at selected frequency points. In the first step, only mass and stiffness matrices are updated while keeping the uncalibrated viscous damping matrix constant. In the second step, the damping matrix is updated via changes on the selected unknown modal damping ratios. By using a stacking procedure of the presented error function that combines multiple data sets, adverse effects of noise on the estimated modal damping ratios are decreased by averaging the FRF amplitudes at resonant peaks. The application of this methodology is presented utilizing experimentally obtained data. The presented algorithm can perform an accurate structural identification via model updating, with a viscous damping matrix that captures the variation of the modal damping ratios with natural frequencies as opposed to other conventional proportional damping matrix formulations.     

Prediction of typhoon design wind speed with cholesky decomposition method

Typhoon simulation method that integrates typhoon wind field model, probability distributions of typhoon key parameters, and Monte Carlo simulation method has long been used to predict typhoon design wind speeds of structures. In the research, the empirical typhoon wind field model with a novel parameter B model of Holland's radial pressure profile is first introduced and validated with typhoon Hagupit's simulation. The results show that relatively good typhoons can be simulated with this empirical typhoon wind field model. Then, the cholesky decomposition method used in typhoon simulation method is proposed that allows achieving all correlated typhoon key parameters simultaneously. Finally, the cholesky decomposition method is used to generating typhoon key parameters in Hong Kong, and typhoon design wind speeds for different return periods are predicted with typhoon simulation method. In addition, typhoon design wind speeds derived from historical typhoon key parameters and typhoon key parameters generated without considering cholesky decomposition method are also predicted, respectively. The predicted typhoon design wind speeds are compared and the results demonstrate that the cholesky decomposition method should be incorporated into typhoon simulation method.     

Analytic wavelet transformation‐based modal parameter identification from ambient responses

Analytic wavelet transform (AWT) based on Gabor wavelet function overcomes the deficiency of the time‐domain localization of traditional Fourier transform and the limitation of the constant resolution in the time‐frequency domain of short‐time Fourier transform. The identification of modal parameters of structures may be carried out by both the amplitude and phase frequency information revealed by resorting to matching mechanism between the wavelet function and complex‐valued signal. By applying the AWT in conjunction with the well‐known random decrement technique, this paper analyses the time‐frequency resolution of Gabor wavelet and the process of identifying structural modal parameters. The method of selecting the parameters of Gabor wavelet function and the formula determining the usable lengths of signal are thus proposed. Eventually, the efficiency of the present method is confirmed by applying it to a numerical simulation data without and with noise contamination of a three degree‐of‐freedom (3DOF) structure with the closely spaced natural frequencies and to ambient vibration full‐scale measurements of a super high‐rise building—Shanghai Jin Mao Building excited by wind. Copyright © 2010 John Wiley & Sons, Ltd.