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.     

Variational mode decomposition based modal parameter identification in civil engineering

An out-put only modal parameter identification method based on variational mode decomposition (VMD) is developed for civil structure identifications. The recently developed VMD technique is utilized to decompose the free decay response (FDR) of a structure into to modal responses. A novel procedure is developed to calculate the instantaneous modal frequencies and instantaneous modal damping ratios. The proposed identification method can straightforwardly extract the mode shape vectors using the modal responses extracted from the FDRs at all available sensors on the structure. A series of numerical and experimental case studies are conducted to demonstrate the efficiency and highlight the superiority of the proposed method in modal parameter identification using both free vibration and ambient vibration data. The results of the present method are compared with those of the empirical mode decomposition-based method, and the superiorities of the present method are verified. The proposed method is proved to be efficient and accurate in modal parameter identification for both linear and nonlinear civil structures, including structures with closely spaced modes, sudden modal parameter variation, and amplitude-dependent modal parameters, etc.     

大跨网壳结构非一致激励竖向地震响应分析

考虑大跨结构的地震响应随地震动空间变化的特性,研究非一致激励下大跨结构的运动方程,运用虚拟激励法的原理对非一致激励下的大跨网壳结构的地震响应进行分析,在ANSYS软件中将非一致激励考虑为静力计算和谐响应计算。通过对平面直径为80 m的单层球面网壳结构的算例分析,得到了竖向地震作用下网壳结构的地震响应变化规律,并与一致激...     

Wavelet-Based Structural Health Monitoring of Earthquake Excited Structures

Abstract:   The article presents a wavelet-based structural health monitoring technique for structures subjected to an earthquake excitation utilizing the instantaneous modal information. The instantaneous mode shape information is first extracted from the vibration response data collected during an earthquake event by using a wavelet packet sifting process. A confidence index (CI) is proposed to validate the results obtained. The identified normalized instantaneous mode shapes in conjunction with the corresponding CIs can be effectively used to monitor damage development in the structure. The effectiveness of the proposed approach is illustrated for two damage scenarios, sudden stiffness loss and progressive stiffness degradation, and different base excitations including three real earthquake signals and a random signal. Consistently good results were obtained in all cases. Issues related to robustness of the method in the presence of a measurement noise and sensitivity to damage severity are discussed.     

Damage Identification for Hysteretic Structures Using a Mode Decomposition Method

This article investigates structural health monitoring (SHM) of multidegree of freedom (MDOF) structures after major seismic or environmental events. A recently developed hysteresis loop analysis (HLA) SHM technique has performed robustly for single degree of freedom (SDOF) and single mode dominant MDOF structures. However, strong ground motions can trigger higher vibration modes, resulting in irregular hysteresis loops and making this otherwise robust identification difficult. This study presents a new filtering tool, enabling reconstruction of single mode dominant restoring force‐displacement loops which can be readily used for HLA. The proposed filtering tool is based on a classic modal decomposition using optimized mode shape coefficients. The optimization process is carried out in a modal space and is based on decoupling frequency response spectra of interfering modes. Application of modal decomposition using the optimized mode shape coefficients allows for reconstruction of single‐mode dominant hysteresis loops, which can be effectively identified using HLA. The proposed filtering tool is validated on the reconstruction of hysteresis loops on an experimental bridge pier test structure with notable contributions from at least two modes. The results show the method eliminates the influence of all higher modes that contain significant energy content and yields the reconstruction of “smooth” single mode dominant hysteresis loops. The resulting SHM analysis on the reconstructed experimental hysteresis loops identified degradation in the elastic stiffness profiles, indicating damage within the structure and matching prior published results based on physical inspection of damage. The overall method presented increases the breadth of potential application of the HLA method and can be readily generalized to a range of MDOF structures.     

Experimental researches on sliding mode active vibration control of flexible piezoelectric cantilever plate integrated gyroscope

The flexible appendages of spacecrafts in aerospace applications demand to be lighter and larger. Thus, they are susceptible to excessive vibration response due to external disturbances or attitude maneuvering. Some of the flexible appendages are cantilever plate structures, such as solar panels and plate shape antennas. Usually, the coupled bending and torsional vibration of cantilever plate will be caused. To decouple the bending and torsional vibration for measuring and driving, gyroscope and PZT patches are used as sensors and actuators by utilizing optimal placement. The motion of equation of the presented piezoelectric plate system is derived. And a kind of discrete-time sliding mode variable structure control (VSC) algorithm is proposed to suppress vibration of the flexible plate. The experimental comparison studies are conducted. The experiments demonstrate that the proposed methods can suppress vibration significantly for cantilever plate.     

Coupled lateral-torsion vibration of asymmetric shear-wall structures

This paper presents an analysis of dynamic performance of asymmetric shear-wall structures. In the analysis, the asymmetric shear-wall structure is replaced by an equivalent thin-walled beam with lateral flexure and warping torsion deformations. Due to the asymmetry of the floor plan, the natural vibration of the structure is a coupled vibration, where lateral flexure vibrations in two orthogonal principal directions couple with a warping torsion vibration. Based on the continuum technique and the D'Alembert's principle, the governing differential equation of natural vibration and the corresponding eigenvalue problem for asymmetric multi-bent wall structures are derived. By employing the Galerkin technique, a method of solution is proposed for analysis of coupled vibration of generally asymmetric shear-wall structures and for estimate of the coupled natural frequencies and associated mode shape in coupled vibration. Results obtained from the proposed method for the example structure show good agreement with those of finite element analysis. It has been shown that the proposed analysis provides an efficient and accurate means of dynamic analysis of asymmetric shear-wall structures in coupled vibration.     

非比例滞变阻尼线性体系的反应谱CCQC法

基于比例阻尼体系建立的振型分解反应谱法应用广泛,是各国规范常用的结构地震作用效应计算方法,直接将其用于非比例阻尼体系(如设置耗能阻尼器的结构)是不合理的.为拓展规范反应谱法的适用范围,在基于复阻尼模型的滞变阻尼模型复模态叠加法基础上,该文结合虚拟激励法和平稳随机理论,推导基于滞变阻尼模型的反应谱CCQC (comple...     

Generalized SDOF system for seismic analysis of concrete rectangular liquid storage tanks

This paper presents a simplified method using the generalized single degree of freedom (SDOF) system for seismic analysis and design of concrete rectangular liquid storage tanks. In most of the current design codes and standards for concrete liquid storage tanks, the response of liquid and tank structures is determined using rigid boundary conditions for the determination of hydrodynamic pressures. Also, the lumped mass approach is used for dynamic analysis. However, it has been shown that the flexibility of a tank wall increases the hydrodynamic pressures as compared to the rigid wall assumption. On the other hand, the consistent mass approach reduces the response of liquid containing structures as compared to the lumped mass approach. In the proposed method, the consistent mass approach and the effect of flexibility of a tank wall on hydrodynamic pressures are considered. The prescribed vibration shape functions representing the first five mode shapes for the cantilever wall boundary condition are studied. The application of the proposed shape functions and their validity are examined using two different case studies including a tall and a shallow tank. The results are then compared with those using the finite element method from a previous investigation and ACI 350.3 commonly used in current practice. The results indicate that the proposed method is fairly accurate which can be used in the structural design of liquid containing structures. It is also concluded that the effect of the second mode should also be considered in the dynamic analysis of liquid containing structures.     

Image analyses for video-based remote structure vibration monitoring system

Video-based vibration measurement is a cost-effective way for remote monitoring the health conditions of transportation and other civil structures, especially for situations where accessibility is restricted and does not allow installation of conventional monitoring devices. Besides, video-based system is global measurement. The technical basis of video-based remote vibration measurement system is digital image analysis. Comparison of the images allow the field of motion to be accurately delineated. Such information is important to understand the structure behaviors including the motion and strain distribution. This paper presents system and analyses to monitor the vibration velocity and displacement field. The performance is demonstrated on a testbed of model building. Three different methods (i.e., frame difference method, particle image velocimetry, and optical Flow Method) are utilized to analyze the image sequences to extract the feature of motion. The Performance is validated using accelerometer data. The results indicate that all three methods can estimate the velocity field of the model building, although the results can be affected by factors such as background noise and environmental interference. Optical flow method achieved the best performance among these three methods studied. With further refinement of system hardware and image processing software, it will be developed into a remote video based monitoring system for structural health monitoring of transportation infrastructure to assist the diagnoses of its health conditions.     

高层建筑不规则结构多维地震效应组合研究

首先建立了不规则偏心结构在三维平动地震动作用下的振型分解方法，探讨了振型的组合方法，并建议了各分量的地震效应组合的SRSS方法。通过多维地震作用下的时程分析与单维地震作用下的时程分析，得出了多维地震的结构内力效应相对于单维地震结构内力效应的增值情况。统计了双向水平地震动同时作用下地震效应值与两正交水平地震动分别单独作用按SRSS方法的组合值之间的比值，根据统计结果对SRSS方法进行系数修正，从而可以用反应谱方法进行双向地震动作用下的抗震分析。     

多变量灰色系统预测模型在深基坑围护结构 变形预测中的应用

 深基坑围护桩体上各监测点之间的变形是相互影响的，在现代信息化施工过程中，对围护桩体变形的预测应该考虑到监测点之间的相关信息，应该从变形观测系统的高度统一来描述变形体的整体变形趋势和变形规律，从整体上对变形观测的数据进行正确的处理，建立合理的模型，对变形值作出准确的预报。基于这一思想，通过对传统的单点GM(1，1)模型的扩展，考虑n 个点之间相互关联和影响，以MATLAB语言编程，实现对变形体上相互关联的多点变形预测模型的建模和预测，并运用该模型对北京市地铁奥运支线深基坑的围护桩变形进行预测。研究结果表明，预测值与实测值吻合较好，能够更为准确地预测出后续施工进程中围护桩体的水平位移，在指导该工程信息化施工和规避工程风险等方面起到积极的作用。同时通过与传统GM(1，1)模型预测结果的比较，证明了多变量灰色系统预测模型具有更高的准确性，显示了该方法进行深基坑变形预测的有效性。     

大跨度屋盖结构的等效静风荷载

采用完全二次型组合(CQC)方法可以对复杂大跨度屋盖结构的风振响应做精确的分析,但由于此类结构存在模态密集、模态间耦合等问题,在等效静风荷载(ESWL)计算方面,适用于高层建筑结构顺风向抖振分析的阵风因子法对于此类结构并不适用,故ESWL的计算要复杂得多。本文结合刚性建筑模型的风洞同步多点测压试验,提出了测点影响系数(TIC)方法实现了测点风压系数向结点荷载的快捷转换,在采用CQC方法精确分析结构风振响应的基础上,将模态响应进行组合而形成一组等效的时变荷载,从而将原来复杂的动力学问题转换为简单的准静态问题,最后应用荷载响应相关(LRC)方法计算了结构的等效静风荷载。本文方法适用于任意复杂结构的ESWL计算,将其应用于某奥运场馆的风振分析和ESWL计算,结果显示了这种方法的有效性。     

非正交阻尼体系地震反应的非经典振型分解反应谱方法

本文根据随机振动理论,提出了地震作用下非正交阻尼线性体系动力反应的非经典振型分解反应谱方法,该法可为工程抗震设计所应用。     

复杂结构的模态选取方法及在连体结构中的应用

针对复杂结构的各阶模态在地震反应中贡献悬殊,提出了基于模态参与因子的模态分析方法,以便于分析结构的动力特性和采用反应谱方法时结构反应的分析计算。通过动力特性分析和地震反应计算,验证了该方法的可靠性,并指出连体结构模态耦合复杂,高阶模态参与的反应较大,同时指出,增加连接层数可以使薄弱单体的结构性能得到较好的改善。     

组合隔震技术在高烈度区复杂高层结构中的应用研究

为探讨近断层的复杂高层建筑结构的隔震设计要点,结合某高层医院建筑结构设计实例,研究9度设防强地震输入、体型特别不规则和高预期抗震性能目标条件下采用隔震技术的适应性及对应措施,提出发挥不同隔震器件和减震装置性能特点的组合隔震技术方法。结果表明,组合隔震可减小隔震橡胶支座面压和水平变形,减少塔楼偏置引起的结构扭转效应、竖向高位收进引起的高振型效应,结构构件损伤程度和范围大幅降低,屈服耗能机制更为合理,有效提升了建筑结构的抗震能力。分析比较近场速度脉冲型地震波与考虑1.5近场增大系数的常规地震波作用下复杂高层隔震结构的地震响应差别,结果表明,在速度脉冲型地震波作用下的隔震层位移、上部结构层间位移角及层剪力均大于考虑1.5近场增大系数的常规地震波,采用1.5近场增大系数不能包络近场地震效应,隔震设计时应慎重考虑。     

Structural dynamic parameter identification of Saige building based on distributed synchronous acquisition method

在大型复杂工程结构上进行现场模态测试时，由于结构规模体量大并存在空间隔断，导致数据采集设备与传感器之间快速布设数据传输线困难。因此，有必要解决不同位置分布式同步采集设备时间精确同步问题，研发易于快速安装的分布式数据采集和无线传输设备。为此，提出基于“北斗”卫星授时的结构振动分布式同步采集算法，集成分布式同步采集硬件与研发数据在线采集和无线传输软件，获取大型复杂工程结构不同空间位置时间同步动态响应，基于随机子空间算法自[JP2]动识别工程结构服役状态下真实的模态参数。在赛格大厦振动事件溯源工作中，该系统成功捕捉到5月20日12:00—13:00[JP]结构共振时第69层与桅杆底部的加速度响应，发现四次共振均以频率2.12 Hz振动主导。基于该系统在环境激励条件下的现场模态测试，识别结构前19阶动力学参数，发现频率2.12 Hz是主体结构弯扭耦合和桅杆面内对称振动模态。基于现场激振测试识别频率2.12 Hz对应的阻尼比，发现阻尼比随着振幅的增加突然减小然后逐步增加，较低的阻尼比是导致赛格大厦发生共振的原因之一。     

基于分布式同步采集的赛格大厦结构动力学参数识别

在大型复杂工程结构上进行现场模态测试时,由于结构规模体量大并存在空间隔断,导致数据采集设备与传感器之间快速布设数据传输线困难。因此,有必要解决不同位置分布式同步采集设备时间精确同步问题,研发易于快速安装的分布式数据采集和无线传输设备。为此,提出基于“北斗”卫星授时的结构振动分布式同步采集算法,集成分布式同步采集硬件与研发数据在线采集和无线传输软件,获取大型复杂工程结构不同空间位置时间同步动态响应,基于随机子空间算法自动识别工程结构服役状态下真实的模态参数。在赛格大厦振动事件溯源工作中,该系统成功捕捉到5月20日12:00—13:00结构共振时第69层与桅杆底部的加速度响应,发现四次共振均以频率2.12 Hz振动主导。基于该系统在环境激励条件下的现场模态测试,识别结构前19阶动力学参数,发现频率2.12 Hz是主体结构弯扭耦合和桅杆面内对称振动模态。基于现场激振测试识别频率2.12 Hz对应的阻尼比,发现阻尼比随着振幅的增加突然减小然后逐步增加,较低的阻尼比是导致赛格大厦发生共振的原因之一。     

Application research of combined isolation technology in complex high-rise building in high seismic intensity region

为探讨近断层的复杂高层建筑结构的隔震设计要点，结合某高层医院建筑结构设计实例，研究9度设防强地震输入、体型特别不规则和高预期抗震性能目标条件下采用隔震技术的适应性及对应措施，提出发挥不同隔震器件和减震装置性能特点的组合隔震技术方法。结果表明，组合隔震可减小隔震橡胶支座面压和水平变形，减少塔楼偏置引起的结构扭转效应、竖向高位收进引起的高振型效应，结构构件损伤程度和范围大幅降低，屈服耗能机制更为合理，有效提升了建筑结构的抗震能力。分析比较近场速度脉冲型地震波与考虑1.5近场增大系数的常规地震波作用下复杂高层隔震结构的地震响应差别，结果表明，在速度脉冲型地震波作用下的隔震层位移、上部结构层间位移角及层剪力均大于考虑1.5近场增大系数的常规地震波，采用1.5近场增大系数不能包络近场地震效应，隔震设计时应慎重考虑。     

吊顶系统自振特性分析及试验研究

为研究上部支承结构和吊杆构造对吊顶自振特性的影响,对一个每层附有吊顶的空间钢框架进行了振动台试验。通过快速傅里叶变换(FFT)和随机子空间识别(SSI)两种模态识别方法获得了吊顶系统的自振频率和阻尼比,给出了吊顶阻尼比的建议值为2%~5%。对主附结构（上部支承结构+吊顶）的自振特性进行了数值模拟,结果表明：吊杆构造形式对吊顶的第1阶水平和竖向模态没有明显影响,上部支承结构自振频率的不同会对吊顶的竖向模态产生影响,而对水平模态没有明显影响。通过改变上部支承结构的截面尺寸和附加质量对主附结构的竖向模态进行了参数化分析,得到仅考虑附加吊顶质量的上部支承结构的第1阶竖向自振频率小于不考虑上部支承结构影响的吊顶第1阶竖向自振频率fb时,主附结构的第1阶竖向振型表现为上部支承结构和吊顶的整体振动,而大于fb时,第1阶竖向振型表现为吊顶的独立振动。