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%.     

Reduction of traffic-induced vibration of two-girder steel bridge seated on elastomeric bearings

Reinforcing end-cross beam and removing bumps at expansion joints of bridges are proposed to reduce the traffic-induced vibration and to enhance the deck resistance near the expansion joint of a two-girder steel bridge with elastomeric bearings at each support. The reduction effect is investigated by means of a three-dimensional traffic-induced dynamic analysis. This study indicates that traffic-induced acceleration responses as well as dynamic reaction force of the bridge with the elastomeric bearings are greater than those of the bridge with steel pin bearings. It is observed that reinforcing the end-cross beam reduces traffic-induced vibrations regardless of bearing types, and also removing bumps is the most effective in reducing the dynamic reaction force of the bridges. Especially, for the bridge with elastomeric bearings, the maintenance of bumps near expansion joints is very important to improve not only expanding life span of the expansion joint but also the vibration serviceability of bridges.     

Operational modal testing and FE model tuning of a cable-stayed bridge

The paper presents the results obtained from the application of different output-only modal identification techniques to ambient response data collected in two dynamic tests of a cable-stayed bridge and the subsequent finite element model correlation analysis. The first test, performed by using a traditional data acquisition system with servo-accelerometers, was aimed at investigating the vertical dynamic characteristics of the bridge. In the second test, an innovative radar vibrometer was used for non-contact measurement of deflection time series of the forestays and the identification of local natural frequencies of the stay cables.In the theoretical study, vibration modes were determined using a 3D Finite Element model of the bridge and the information obtained from the field tests, combined with a classic system identification technique, provided a linear elastic model, accurately fitting the modal parameters of the bridge in its present condition.     

Inspection,condition evaluation and replacement of elastomeric bearings in road bridges

This paper presents the results of an inspection campaign as well as condition evaluation and replacement of more than 1000 elastomeric bridge bearings under service on the Isfahan state highway bridges constructed before 1990. It is the first comprehensive survey of this kind. The research was accomplished through inspection surveys, analysis of existing bridge maintenance data, condition evaluation and replacement of a significant portion of the inspected bearings and expert interviews. Inspection surveys and analysis of extracted data identified the problems and their causes and the merits and potential improvement of performance of each one of the inspected elastomeric bearings. Replacement of the damaged bearings with new ones was performed based on the results of this stage. The expert interviews investigated the practices of Isfahan and surrounding states regarding the selection of bearing manufacturers, the performance and the quality control of elastomeric bearings.     

基于模态柔度改变率对系杆拱桥的损伤识别

研究了适用于系杆拱桥拱肋结构的损伤识别方法,由于模态柔度对结构损伤的高灵敏性,采用模态柔度改变率作为指标,考虑各种损伤情况,运用该指标进行仿真分析,通过计算的数值表明,模态柔度改变率法可以准确有效地判断损伤位置,定性地判断同一位置处的损伤程度.     

ANSYS在巨型钢框架结构模态分析中的应用

对有限元模态分析基本理论及ANSYS环境下模态分析的过程进行了论述,通过对复杂巨型钢框架结构模态计算分析,得到了此模型的固有频率和相应的振型,为巨型钢框架结构的进一步动力分析提供了依据。     

某脱气仓结构振动模态分析

结合具体工程实例,针对大型脱气仓结构是否设置脱气仓设备参与结构分析进行了研究,讨论了脱气仓设备的设置对结构振动模态的影响,结果表明,设置脱气仓设备后使结构的模态响应发生改变,容易导致脱气仓设备的局部振动。     

Experimental and analytical system identification of Eynel arch type steel highway bridge

This paper describes a full scale arch type steel highway bridges, its finite element modelling and Operational Modal Analysis. Eynel Highway Bridge which has arch type structural system with a total length of 336 m and located in the Ayvac?k county of Samsun, Turkey is selected as a case study. The bridge connects the villages which are separated with Suat U?urlu Dam Lake. The three dimensional finite element model is constructed using project drawings and an analytical modal analysis is then performed to generate natural frequencies and mode shapes in the three-orthogonal directions. The ambient vibration tests on the bridge deck under natural excitation such as traffic, human walking and wind loads are conducted using Operational Modal Analysis. Sensitive seismic accelerometers are used to collect signals obtained from the experimental tests. To obtain experimental dynamic characteristics, two output-only system identification methods are employed namely, Enhanced Frequency Domain Decomposition method in the frequency domain and Stochastic Subspace Identification method in time domain. The correlation between the finite element model and experimental results is studied. Good agreement is found between dynamic characteristics in the all measurement test setups performed on the bridge deck. It is demonstrated that the ambient vibration measurements using Enhanced Frequency Domain Decomposition and Stochastic Subspace Identification methods are enough to identify the most significant modes of steel highway bridges. It is seen that there are some differences between analytical and experimental natural frequencies and experimental natural frequencies are generally bigger than the others.     

桥梁结构损伤识别方法的研究进展

简要介绍了桥梁结构损伤识别方法的发展和当前研究现状,对桥梁各类损伤识别方法进行了分析和总结,展望了桥梁结构损伤识别方法的研究和发展方向,以期进一步提高损伤识别的精度并将其成功运用到工程实例中。     

某大跨度钢结构人行天桥的振动特性分析与研究

针对某大跨度钢结构人行天桥出现的振动问题,对该人行天桥进行了全桥动力测试,利用有限元分析软件SAP2000建立该结构的有限元模型,利用基于实测数据的频谱分析以及模态分析的方法对其出现的振动问题进行分析,为同类结构的动力特性研究提供参考.此外,改变了以往在此类问题中仅考虑行人对振动产生影响的局限性,分别从通行行人及通行车辆这两个因素对该天桥振动的原因进行了深入分析,从而找到了造成该天桥产生实测振动特性的主要原因,并对结构出现过大侧向振动给出了合理解释.相关信息可为后继结构的加固改造工作提供参考,并进一步提出了结构改造措施与建议.     

某高速公路桥梁偏位事故原因分析探讨

通过对某高速公路桥梁进行详细现场检测及理论计算,分析了桥梁发生梁体偏移的原因,深入探讨了桥下不合理土方堆积对桥梁的损伤情况,并提出了相应的处治措施,为类似情况下的事故原因分析提供有益的借鉴参考。     

某高速公路大桥病害检测分析

本文主要针对某高速公路大桥进行病害检测分析,通过对桥面系、支座、上部结构和下部结构的检查,以及对桥梁材质状况和状态参数检测,指出了该桥在实际检测中出现的病害状况,并提出了桥梁健康养护和维修的建议。     

基于导波传递分析的板肋钢桥面板振动特性研究

从弯曲波导波传递特性角度出发,结合振动试验和数值仿真开展钢桥板肋桥面板的动力特性和振动机理研究。首先开展板肋钢桥面板室内振动试验;继而运用模态叠加有限元法建立经试验验证的三维有限元动力模型,进行板件振动能量计算,并基于有限元模式分析法建立导波模型,对结构面外弯曲波频散特性和导波类型展开研究;最后对比顶板厚度、肋板厚度以及肋板间距三种设计参数对板件振动能量和弯曲波导波特性的影响。结果表明：经试验测试单边悬挂约束下顶板和肋板振动响应的优势频段出现在300Hz和400Hz,且肋板边缘测点的振动能量更大;边界固结约束下较薄的顶板具有较高振动能量峰值和较低的峰值频率;从导波传递角度来看,板肋桥面板弯曲波频散曲线均出现了通频带与衰减带间隔出现的现象,导波模态数随顶板和肋板厚度的增长而减小,顶板厚度对板件面外振动衰减带影响最大,其中带宽最大差值达110Hz,因此可通过顶板厚度对结构的面外弯曲波振动衰减带进行有效控制。     

桥上弹性支承块式无砟轨道垂向刚度研究

利用通用有限元软件ANSYS的APDL参数化建模技术,建立桥上弹性支承块无砟轨道模型。利用ANSYS的模态分析功能,分别计算块下刚度不变而轨下刚度变化和轨下刚度不变而块下刚度变化两种情况下模型频率,并分析频率的变化规律,得出一定的结论。     

自锚式悬索桥动力性能研究

结合一座自锚式悬索桥的工程设计实例,建立了该桥的空间力学计算模型,利用子空间迭代法计算该桥梁结构的自振频率和振型,分析了自锚式悬索桥的动力特性,探讨了桩—土相互作用后对结构的影响。     

公路桥梁施工临时支架稳定性计算与分析

对桥梁施工临时支架倒塌的常见原因进行了分析,对影响支架稳定性的因素和支架稳定性计算方法进行了总结,以实际工程为例,对工程设计中的支架设计方法及计算内容进行了分析与讨论,并对现有支架的施工方法提出了合理的建议,以达到指导同类工程设计施工的目的。     

Monitoring the dynamic characteristics of an urban bridge before,during and after widening

The dynamic characteristics of a multi-span pre-stressed concrete urban bridge before, during and after widening operations have been studied. The widening operations have been carried out by adding two new bridges on the either sides of the old bridge. The decks of the new bridges have been structurally separated from the old one by two longitudinal joints on the either side of the old bridge. The dynamic characteristics have been extracted from operational modal tests in three phases during different stages of the widening operations. The dynamic interaction between the new parts and the old part of the bridge has also been investigated. The results show that after the completion of the widening works, and when the whole bridge was placed in service condition, this interaction affects the natural frequencies of almost all the vibration modes of the bridge. It was also found that the longitudinal joints were unable to effectively isolate the new parts from the old part. Finally, in order to achieve a consistent behaviour in the first bending mode of the new and old bridges, a geometrical index has been introduced. This index includes both the effects of stiffness and mass properties of the bridge deck. In widening projects, where the span lengths, material properties and support conditions of the two bridges are taken the same, adopting equal geometrical indices leads to almost equal values of the natural frequencies and similar mode shapes in the first bending mode. The proposed index can be used in the initial design stage for such projects.     

成乐高速公路桥梁病害成因分析及对策

论述了四川成乐高速公路桥梁“5·12”汶川大地震后检测的主要成果,对桥梁病害进行了归类和成因分析,借鉴国内外经验,对相关病害提出了处治对策,以确保公路桥梁安全运营。     

高速公路桥头跳车及桥梁养护

叙述了高速公路桥头跳车的可能性,分析了桥头跳车的现象、原因、危害与对策,同时还探讨了桥梁养护、检测、计算、承载力评价、维修加固与钢筋混凝土及预应力混凝土桥梁的耐久性.     

地铁振动造成大跨度人行天桥抖振的机理分析

对某钢结构大跨度人行天桥在地铁振动作用下的受迫抖振做现场实桥测试,利用频谱分析和有限元分析方法,对天桥上部结构进行模态参数分析。根据工程振动理论得出,由地铁振动诱发的地基振动优势频率与天桥上部结构低阶自振频率相近,由此引发结构共振效应,基础振动相对运动传递率过高是造成天桥梁体抖振的主要原因。