Vibration-based operational modal analysis of the Mikron historic arch bridge after restoration

This research presents finite element modelling, vibration-based operational modal analysis, and finite element model updating of a restored historic arch bridge. Mikron historic bridge, constructed on F?rt?na River in Rize, Turkey, is the subject of this case study. The General Directorate for Highways of Turkey repaired the bridge's main structural elements, arches, sidewalls, and filler material in 1998. To construct a 3D finite element model of the bridge, ANSYS finite element software estimated the analytical dynamic characteristics. Induced ambient vibrations such as human walking and wind excited the model bridge to allow measurement of the bridge's responses. Enhanced frequency domain decomposition in frequency domain and stochastic subspace identification in time domain methodologies extracted experimental dynamic characteristics. A comparison of the analytical and experimental results showed significant agreement between mode shapes, but some differences in natural frequencies appeared. Consequently, updating the finite element model of the bridge by changing boundary conditions minimised the differences between analytical and experimental natural frequencies. After the finite element model updating process, the differences between natural frequencies declined from 7% to 2%.     

Real-time wireless vibration monitoring for operational modal analysis of an integral abutment highway bridge

Remote structural health monitoring systems employing a sensor-based quantitative assessment of in-service demands and structural condition are perceived as the future in long-term bridge management programs. However, the data analysis techniques and, in particular, the technology conceived years ago that are necessary for accurately and efficiently extracting condition assessment measures from highway infrastructure have just recently begun maturation. In this study, a large-scale wireless sensor network is deployed for ambient vibration testing of a single-span integral abutment bridge to derive in-service modal parameters. Dynamic behavior of the structure from ambient and traffic loads was measured with accelerometers for experimental determination of the natural frequencies, damping ratios, and mode shapes of the bridge. Real-time data collection from a 40-channel single network operating with a sampling rate of 128 Hz per sensor was achieved with essentially lossless data transmission. Successful acquisition of high-rate, lossless data on the highway bridge validates the proprietary wireless network protocol within an actual service environment. Operational modal analysis is performed to demonstrate the capabilities of the acquisition hardware with additional correlation of the derived modal parameters to a Finite Element Analysis of a model developed using as-built drawings to check plausibility of the mode shapes. Results from this testing demonstrate that wireless sensor technology has matured to the degree that modal analysis of large civil structures with a distributed network is a currently feasible and a comparable alternative to cable-based measurement approaches.     

大跨度连续刚构桥模态分析与测试

采用大型有限元软件midas civil 2010对东江南特大桥特征值进行分析,取前3阶竖向振动频率与实际值进行对比,并将桥梁振动模态实验检测方法用于无损检测中,指出采用该方法对桥梁结构进行动力测试,无需封桥,值得推广。     

Investigation of a historic masonry structure by numerical and operational modal analyses

This paper presents the results of model calibration conducted on a historical mosque called Hafsa Sultan in Manisa, Turkey. The finite element model of the mosque was calibrated by the use of the results obtained from ambient vibration tests of the structure. In order to develop a solid model of the structure, the dimensions of the structure, defects such as cracks and material degradations in the structure, and the materials used in different parts were identified. For the evaluation of the material properties of the structure, nondestructive and destructive testing methods were used. The numerical and experimental modal parameters of the structure were obtained by finite element method (FEM) and Operational Modal Analysis (OMA), respectively. The natural frequencies and corresponding mode shapes were obtained from both FEM and OMA and compared with each other. While a good compatibility was achieved between mode shapes, some differences between natural frequencies occurred. It was thought that the differences resulted from variations in the Young's modulus of masonry, cracks in elements or boundary conditions. Therefore, the finite element model was calibrated by changing material parameters. Finally, a more realistic numerical model of the mosque was put forward and the results were discussed in detail. Copyright © 2015 John Wiley & Sons, Ltd.     

钢管混凝土拱桥模型的理论和试验模态分析

在环境激励条件下,仅用测得的输出响应识别结构的模态参数越来越受到重视.首先,用自然激励技术和特征系统实现算法对一个悬臂槽钢进行了模态参数识别,并与已知的有限元结果进行了比较,吻合较好,从而证明了该模态识别技术和所使用的整套仪器的可信度;然后,用该方法对一个较复杂的钢管混凝土拱桥模型进行了模态参数识别,并与ANSYS建立的有限元模型进行了比较,指出了有限元建模过程的误差和需要改进的地方.     

满堂支架现浇预应力混凝土箱梁桥的施工技术

桥梁建设中,现浇预应力箱梁具备独特的施工优势,结合工程实例,从基础施工展开论述,着重阐述了满堂支架预应力箱梁桥的施工工艺和关键技术,提出施工技术人员必须明确其基本特征,细化施工流程,强化施工管理,进而全面优化桥梁项目的建设质量。     

考虑地形影响和多点激励的大跨高墩桥地震响应分析

提出一种综合考虑行波和地形影响的大跨结构在多点输入下的地震响应分析方法。首先计算P波在多种角度入射下两座山峰以及其间自由场地的时程响应,并以此作为两座山峰之间大跨桥梁的桥台及桥墩基础多支承点处的地震输入,这种地震输入综合了行波和地形的影响。然后基于多点激励下地震响应分析方法,编制有限元分析程序,在此基础上分析了考虑行波和地形综合影响下一座360m4跨高墩连续刚构桥的多点激励地震响应。从分析结果看,考虑地形效应和不考虑地形效应的差别较大,不考虑地形效应可能会较小的估计结构的内力响应。因此,大跨度结构地震响应分析应考虑地形的影响。本文分析结果可供抗震设计参考。     

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.     

考虑轨道不平顺全概率分布的车桥随机分析方法

轨道不平顺是车桥耦合系统最主要的激励之一,其高维的随机性导致车桥耦合确定性计算模型不能精确反映实际系统动力响应的离散性。为了完整地反映实际线路中的轨道不平顺信息,文章建立一种适用于车桥耦合随机系统分析的轨道不平顺随机场模型,模型在包含了轨道谱概率、幅值、波长、相位等信息的基础之上,尽可能地减少了参数数量,通过与实测数据对比,该模型的有效性得以验证。此外,将该轨道不平顺随机场模型作为三维车 线 桥耦合时变计算模型的激励源,引入概率密度演化方法,对该耦合系统动力指标的统计特性及动力可靠度进行分析。结果表明,该轨道不平顺随机分析模型产生的空间序列较好地表征了平稳随机过程的谱表达;概率密度演化方法相对于蒙特卡洛方法有着更高的计算效率;不同的动力指标有着不同的均值、均方差、可靠度特征。     

桥梁风洞试验模态参数识别的随机子空间方法

模态参数识别是桥梁风洞试验中的一项重要内容,发展了基于参考点、无需输出协方差估计的识别振动系统模态参数的随机子空间方法,其识别精度和可靠性通过数值算例验证。对状态空间理论中的稳定图作了全面的阐释。根据苏通大桥和苏拉马都大桥主梁三自由度节段模型风洞试验采集到的位移信号,采用随机子空间方法识别了侧弯、竖弯和扭转模态频率和阻尼比,并且与随机搜索方法识别结果进行对比。分析结果表明,随机子空间方法和随机搜索方法识别结果非常吻合,本文发展的随机子空间方法是识别风洞试验桥梁模态参数的一种有效和实用方法。     

运营阶段悬索桥钢筋混凝土加劲桁梁有限元分析方法研究

采用传统分析方法对悬索桥钢筋混凝土加劲桁架结构进行分析,结果表明在运营荷载作用下构件计算内力普遍存在偏大问题。本文考虑结构几何非线性和材料非线性的影响,提出了该类结构杆件刚度考虑混凝土材料非线性影响的模拟方法,对某悬索桥进行了有限元分析及承载能力检算分析,并将计算分析结果与荷载试验结果进行对比分析,结果表明,运营阶段结构内力计算时,几何非线性效应不明显,考虑混凝土构件开裂对杆件刚度的折减影响,使构件受力状况与实际状况更加吻合。     

Response surface‐based finite‐element model updating of a historic masonry minaret for operational modal analysis

This study aimed to use the response surface (RS) method for finite element (FE) model updating, using operational modal analysis (OMA). The RS method was utilized to achieve better agreement between the numerical and field‐measured structure response. The OMA technique for the field study was utilized to obtain modal parameters of the selected historic masonry minaret. The natural frequencies and mode shapes were experimentally determined by the enhanced frequency domain decomposition (EFDD) method. The optimum results between the experimental and numerical analyses were found by using the optimization method. The central composite design was used to construct the design of experiments, and the genetic aggregation approach was performed to generate the RS models. After obtaining the RS models, an attempt was made to converge the natural frequency values corresponding to the five‐mode shapes with the frequency values identified by the experimental analysis. ANSYS software was used to perform 3D finite element (FE) modeling of the historic masonry minaret and to numerically identify the natural frequencies and mode shapes of the minaret. The results of the experimental, initial, and updated FE model were compared with each other. Significant differences can be seen when comparing the experimental and analytical results with the initial conditions.     

转体施工拱桥合龙误差对全桥影响可靠度分析

探讨了转体施工拱桥合龙误差的成因,深入研究了转动轴的定位误差分析,推导出转动轴定位偏差产生跨中合龙偏差的计算公式。通过结构力学方法和平面有限元模型相结合分析了合龙误差对钢箱拱肋的力学性能影响。     

钢筋锈蚀对钢筋混凝土结构动力特性影响数值分析

利用有限元软件ANSYS,对发生钢筋锈蚀后的钢筋混凝土结构进行了数值模拟,探讨了在钢筋不同锈蚀程度的情况下,钢筋混凝土结构固有频率的变化情况,模拟结果表明,钢筋锈蚀对钢筋混凝土梁的固有频率有显著影响,钢筋混凝土梁的固有频率随着钢筋锈蚀程度的加深而呈减小趋势。     

The effects of the repair operations and replacement of the elastomeric bearings on the modal characteristics of a highway bridge

In this paper, the extraction of the dynamic properties of a two span simply supported pre-stressed concrete skew highway bridge has been reported. The experimental work has been carried out according to a predetermined repair program involving the replacement of the elastomeric bearings. The operational modal analysis (OMA) technique has been used for the extraction of the modal properties of the bridge. The dynamic parameters of the bridge have been derived with the use of the frequency domain decomposition (FDD) as well as the stochastic subspace identification (SSI). Five modal tests have been carried out during different stages of the repair operations. One of these tests has been performed under normal traffic and the rest of the experiments have been carried out in the condition of traffic closure. Supporting numerical analyses have demonstrated close agreement between experimental and numerical results. In addition, the effects of the variation of the values of the shear modulus of the elastomeric bridge bearings on the dynamic properties of the bridge have been investigated. As a result of the experimental and numerical studies, it has been demonstrated that some additional retrofit measures also needed to be taken.     

斜拉桥索塔锚固区节段足尺模型试验与分析

对某斜拉桥索塔锚固区节段建立有限元计算模型进行空间应力分析,并与足尺模型试验得出的结果相比较,对该桥塔锚固区工作性能及安全性进行评价。测试分析U形塑料波纹管孔道摩阻系数和钢束伸长值,研究了小半径环向U形预应力束与拉索作用下的锚固区应力与变形情况,提出构造及设计上的建议,为设计与施工提供依据,也可为同类斜拉桥索塔锚固区的受力分析提供借鉴。     

桥梁振动辐射低频噪声评估方法研究

为了研究桥梁交通振动辐射低频噪声的机理和建立相应的数值模拟方法,用车桥耦合振动和空气波传播原理提出桥梁振动辐射低频噪声的计算方法.以一座简支钢桥为例,用格子梁结构计算模型分析车辆通过时的结构振动和由此引起的声压,通过与现场实测结果的对比,验证理论方法分析桥梁振动辐射低频噪声机理的可能性.在此基础上进一步对路面平整性、车辆计算模型等参数的影响进行对比分析,探索路面以及车辆模型对计算结果的影响.结果表明,平整路面可以降低桥梁辐射低频噪声的强度;采用不同的车辆模型对计算得到的声压有一定的影响;为了提高精度需要对高频范围内的桥梁振动计算方法、非平稳信号分析以及声波在边界上吸收、反射等方面进行进一步改进.     

Simplified method of analysis accounting for shear-lag effects in composite bridge decks

This paper proposes a simplified method of analysis for the design of twin-girder and single-box steel-concrete composite bridge decks. Its main advantages rely on (i) the use of the real width of the slab for the whole bridge length when performing the global analysis, i.e. without modifying the deck geometry based on the effective width method, and (ii) its ability to evaluate the normal longitudinal stress distribution on the slab by means of a cross-sectional analysis considering the internal actions obtained from the global analysis. In the latter cross-sectional analysis the properties of the concrete component are based on an effective width calculated using new analytical expressions presented in this paper. The proposed approach is capable of handling different loading conditions, such as constant uniformly distributed loads, envelopes of transverse actions due to traffic loads, support settlements and concrete shrinkage. These analytical expressions have been obtained based on the results of an extensive parametric study carried out by means of the finite element formulation described in the first part of the paper. The accuracy of the proposed approach is validated for a typical four-span bridge with constant cross-section throughout its length against the results obtained based on the finite element method. Finally, a realistic case study of a bridge with varying cross-section is considered to show the robustness of the proposed methodology.     

斜拉索加固悬索桥的参数化分析

为了精确分析斜拉索加固悬索桥主缆的效果,基于悬链线法针对影响斜拉索索力的因素进行研究。以某管线悬索桥为背景,结合现场量测数据,通过参数化分析,提出影响斜拉索索力变化的主要参数为环境温度和加劲梁处斜拉索锚固位置竖向位移。     

预应力钢-混凝土组合连续梁桥预加力效应有限元分析

本文以福州市某钢-混凝土组合连续梁桥为对象,应用ANSYS有限元软件建立空间模型,将有限元值与实桥静载试验值进行比较,从而验证了有限元模型的合理性,提出了考虑预加力效应的截面尺寸优化方案,并在此基础上分析了预加力对结构受力性能的影响。分析结果表明,考虑预加力对截面尺寸优化效应的方案在技术上可行,预加力技术的应用有效地改善了结构的受力性能,且经济效益较显著,可为类似工程的设计与研究提供借鉴。