Vibration of railway bridges under a moving train by using bridge-track-vehicle element

During the last two decades, much attention has been paid to various vibration problems associated with railways. They include the dynamic response of railway bridges and railway tracks at grade under the action of moving trains. However, studies on the role of track structures on the vibration of railway bridges are rather limited. In this paper, a new element called bridge-track-vehicle element is proposed for investigating the interactions among a moving train, and its supporting railway track structure and bridge structure. The moving train is modelled as a series of two-degree-of-freedom mass-spring-damper systems at the axle locations. A bridge-track-vehicle element consists of vehicles modelled as mass-spring-damper systems, an upper beam element to model the rails and a lower beam element to model the bridge deck. The two beam elements are interconnected by a series of springs and dampers to model the rail bed. The investigation shows that the effect of track structure on the dynamic response of bridge structure is insignificant. However, the effect of the bridge structure on the dynamic response of the track structure is considerable.     

Assessment of existing steel railway bridges

A series of dynamic tests, acceleration measurements, evaluation, finite element model simulations and safety index calculations were performed on existing steel railway bridges giving service on railway network. Dynamic tests were fulfilled by using a special test train on these bridges to obtain the dynamic parameters and these parameters were then used to refine the finite element models of the bridges. Once the models have been updated to represent the actual condition, safety indices were calculated for structural components of the bridges for each proposed loading condition. These safety indices were used to calculate failure probabilities of structural members. As the final step, system reliability of the bridges was evaluated based on proposed system models of the bridges. It is believed that this study will provide a reliable background for proposed heavier axle loads resulting from new freight trains by realizing the current condition of bridge structures.     

现有铁路钢桥的评估

对现有铁路钢桥进行一系列的动力试验、加速度测量、评估、有限元模拟和安全指数计算。采用专门列车进行动力试验,并获取动力参数。这些参数还可用于建立桥梁的有限元模型。如果模型能够反映实际工况,就能用于计算每种工况下桥梁结构的安全指数。这些安全指数可用于计算杆件的破坏可能性,因此可采用本模型评估桥梁的可靠性。通过了解现有桥梁结构的实际工况,本研究可为新的货运列车重级荷载研究提供可靠依据。     

Impact of track irregularities and damping on the fatigue damage of a railway bridge deck slab

The structural response of reinforced concrete slabs in railway bridges is strongly influenced by local dynamic effects and, therefore, detailed calculations of internal forces have to be performed for a realistic fatigue assessment. In this context, this paper discusses the influence of track irregularities and modal damping coefficients in the dynamic response and fatigue behaviour of a railway bridge deck slab. For that purpose, track irregularities were measured (at different instants of time) and damping coefficients were determined based on acceleration records for passing trains in a real bridge. The bridge behaviour was calculated using a train–bridge interaction methodology, considering calibrated numerical models of the viaduct and the train. The fatigue damage was quantified through the linear damage accumulation method. This methodology allowed to understand the way track irregularities and damping coefficients affect the magnitude of applied bending moments and fatigue damage in the slab.     

上海长江大桥风-轨道车辆-桥耦合振动及抗风行车准则研究

为确定上海长江大桥轨道交通车辆的抗风行车准则,将风、车、桥三者视为一个交互作用、协调工作的耦合动力系统,通过风洞试验测定主梁及车辆的气动参数,采用自主研发的桥梁结构分析软件BANSYS进行风-车-桥耦合动力分析计算。计算结果表明:桥梁和车辆的响应随风速的增大而增大,风荷载对行车的安全性和舒适性有很大影响。当风速小于20m/s时,车辆可按设计车速90km/h运行;当风速在20～30m/s之间时,车速不应大于60km/h;当风速超过30m/s时,应封闭轨道交通。     

蛇行波长取值方式对钢板梁桥横向振动的影响

随着我国既有线路的大规模提速,铁路货车提速后上承式钢板梁桥横向振幅超限现象日益突出,严重影响货车进一步提速.以轮对随机人工蛇行波为激励,就不同的蛇行波长取值方式对铁路钢板梁桥横向振动的影响进行了探讨.最后指出,20辆车各个轮对蛇行波波长均不同、轮对蛇行波波长随机选取时各速度对应的桥梁横向最大位移小于轮对蛇行波波长均相同时相应速度对应的桥梁横向最大位移值.     

A multidisciplinary approach for fatigue assessment of a steel–concrete high-speed railway bridge on Sesia river

Steel–concrete composite bridge solutions have been more and more exploited in the new high-speed (HS) lines of European railway networks. New design solutions, introduced during a period of quick expansion for railway networks, amplified open problems related to dynamic effects, train–bridge interaction phenomena, fatigue loadings, structural modelling, fatigue life and comfort. In this article, results obtained by long-term dynamic monitoring of Sesia viaduct, a medium span double-box composite bridge of the new Italian HS network, are described and analysed. Structural modal properties were determined in order to evaluate the real-time dynamic behaviour and its correlation with environmental conditions. A suitable numerical procedure was then implemented in order to identify typology, length and velocity of trains crossing the bridge, to evaluate the intensity of deck vertical accelerations as a function of train speed and to obtain a reliable evaluation of real traffic spectra. A final fatigue assessment on welded connections was executed evaluating fatigue spectra by the aforementioned real traffic spectra and assuming S–N curves obtained by suitably executed experimental tests.     

Fatigue assessment of a composite railway bridge for high speed trains. Part I: Modeling and fatigue critical details

Steel bridges for high speed trains may sustain excessive fatigue damage due to stronger dynamic effects induced by the increased train speed. Dynamic tests were carried out on a composite railway bridge for high speed trains. A detailed finite element (FE) model of the bridge was established and validated by the dynamic test results. Six types of structural details in the bridge were considered for fatigue evaluation. The stress history of each concerned detail during a single train passage was generated by the validated FE model. The stress spectrum, obtained through Rainflow cycle counting of stress history, was used to calculate the fatigue damage of each detail, based on the detail category specified S–N design curve and the Palmgren–Miner damage rule. Among various structural details, the load carrying fillet weld around the gusset plate of the diagonal bracing at the bridge bearing is predicted to be the most fatigue critical detail. In this paper, a general methodology for determination of fatigue critical details is presented, which can serve as a basis of enhanced fatigue evaluation by using local stress approaches. In “Part II: conditions for which a dynamic analysis is needed” as the continuation of this paper, fatigue assessment will be investigated based on the dynamic stresses predicted by different approaches, i.e. static analysis considering dynamic amplification factor, direct dynamic analysis with a moving load model or a train–bridge interaction model.     

跨高铁桥梁设计及施工

随着我国高速铁路的快速发展,跨越既有高速铁路的桥梁越来越多.由于铁路建筑界限及安全的要求,与跨越普通铁路的桥梁相比,跨高铁桥梁的跨径一般都较大.研究跨高铁桥梁设计及施工,供类似工程参考.     

Experimental investigation of double composite twin-girder railway bridges

A railway bridge with a double composite section has been proposed to enhance the structural performance of existing twin-girder bridges, because the governing design parameter of railway bridges is flexural stiffness. The concrete deck in negative moment regions is neglected in the design of continuous composite bridges assuming the concrete slab has no resistance to tension. Therefore, the flexural stiffness of the composite section in the negative moment region is reduced, resulting in an increase of the depth of the steel section. In this study, push-out tests on lying studs and mixed stud shear connection with lying and vertical studs were performed to investigate the behavior of the shear connection in the double composite section. In addition, the static strength of the shear connection was evaluated. This study focuses on continuous two girder bridge models of 5m-5m span length with the proposed double composite section. From the static tests on the bridge models, several design considerations were investigated including the effective width, shear connection, and ultimate strength of the double composite section. Based on the test results, design guidelines and innovative twin-girder bridges were suggested.     

Assessment of the dynamic and fatigue behaviour of the Panaro railway steel bridge

The functionality maintenance of European infrastructures like bridges is acquiring more and more importance due to the huge economic losses related to the interruption of their regular service. In particular, fatigue represents one of the most common failure modes occurring in steel and steel–concrete composite bridges: most failures in steel structures are related to fracture and fatigue. Railway bridges endure millions of stress cycles during their life and they are expected to be highly vulnerable to such phenomena. Phenomena like ‘vibration induced’ and ‘distortion induced’ fatigue are still partially uncovered by actual design codes and they represent critical aspects for the assessment of existing bridge remaining life and for the design of new bridges. The European research project FADLESS ‘Fatigue damage control and assessment for railways bridges’, funded by the Research Fund for Coal and Steel, aims at defining innovative technical guidelines for the assessment and control of existing and new bridges with regard to fatigue phenomena induced by vibrations and distortions produced by train passages. The project combines experimental and numerical techniques to study fatigue cracking induced by vibration and distortion phenomena taking into account the dynamic train–bridge interaction effects and the actual traffic spectra on European railway lines. In the present paper, preliminary analyses performed on the Italian case study, the Panaro Bridge, are being reported upon. Results obtained by standard fatigue assessment according to Eurocode rules were compared with the actual fatigue cracks found in the deck secondary components. A preliminary critical review of adopted fatigue assessment methodologies was carried out. Moreover, experimental tests were designed and performed on the bridge in order to identify global and local vibration modes and to evaluate the strain time-histories under train passages of critical details. Finally, experimental global/local mode shapes were compared to numerical results from the preliminary FE bridge model.     

Determination of the critical loading conditions for bridges under crossing trains

A procedure based on experimental and theoretical analyses to identify critical loading conditions on existing metallic railway bridges is presented. This method requires knowledge of the principal modal frequencies, and for this reason, a consolidated and simple procedure to study the bridge dynamics is herein explained. This consists of: preliminary studies; material and dynamic tests; and identification techniques to identify modal parameters and eventual non-linear behaviours. Generally the information collected can be used both to calibrate the bridge model and to obtain the refined frequency response function. In order to avoid high computational effort due to long time-history dynamic analyses by using the bridge model subjected to a series of train crossings, a new frequency domain approach for the identification of critical loading conditions is proposed. Evidence of the influence of the axle spacing and velocity of the vehicle on the dynamic magnification due to the train crossing is shown. The method is based on the construction of an excitation spectrum related to the train axle spacing and the velocity, given the weight of the vehicle. Comparison of the excitation spectrum with the frequency response function allows identification of the load patterns that bring the bridge to resonance conditions and might threaten bridge stability, bearing in mind continual changes in train technology.     

侧风作用下静动态车-桥系统气动特性数值模拟研究

我国现阶段正处于轨道交通建设的高峰时期,线路中桥梁占有相当大的比重,车辆在桥梁上运行时构成车-桥系统共同承受侧向风的作用,车辆和桥梁间存在着显著的相互气动影响。基于数值模拟方法,对侧向风作用下车-桥体系的空气绕流场进行静动态模拟分析,将静态数值模拟气动力系数与风洞试验结果进行对比,基于动态气动统流特性,提出将桥面上方流场分为6个特征区域,并进一步分析风速和车速对车-桥系统气动特性的影响。分析表明,体系绕流状态具有三维特性,气动力随着车速和风速变化显著。研究结论对车-桥系统绕流及静动态气动荷载的确定具有一定的参考价值。     

Design and construction of super-long span bridges in China: Review and future perspectives

Super-long span bridges demand high design requirements and involve many difficulties when constructed, which is an important indicator to reflect the bridge technical level of a country. Over the past three decades, a large percentage of the new long-span bridges around the world were built in China, and thus, abundant technological innovations and experience have been accumulated during the design and construction. This paper aims to review and summarize the design and construction practices of the superstructure, the substructure, and the steel deck paving of the long-span bridges during the past decades as well as the current operation status of the existing long-span bridges in China. A future perspective was given on the developing trend of high-speed railway bridge, bridge over deep-sea, health monitoring and maintenance, intellectualization, standard system, and information technology, which is expected to guide the development direction for the construction of future super long-span bridges and promote China to become a strong bridge construction country.     

中跨横隔板对组合铁路桥梁静力和动力特性的影响(案例分析)

为高速列车而设计的中等跨度多肋铁路桥的桥梁上,混凝土桥面是提供横向刚度的主要构件,但横梁上的作用力是未知的。由于横梁需要现场操作和焊接,所以增加了桥梁的成本。研究了一种横隔板的影响,这种横隔板应用在法国的一个典型的多跨度铁路桥梁上。第一个目的是为了提出一种合适的建模方法,可以被用于评估在这种交通荷载呈横向分布的结构上应用横隔板的作用和有效性。第二个目的是为了探究应用横隔板的必要性。为解决这些问题,建立了一个三维模型和非线性材料本构关系,分析了带有横向横隔板的和不带横隔板的桥面在不同的静力荷载条件下(自重,UIC荷载,TGV)的反应。考虑到桥面的动力特性,TGV采用移动荷载模拟。在动力分析中还考虑到了火车的极限速度。静力和动力分析结果表明:横隔板可能并不是必须采用的,除非桥梁受到意外的侧向力作用。因此,在这些桥梁上也许可以不需要安装横隔板。     

地震作用下高速铁路车-轨-桥系统安全研究进展

桥梁占线比高、列车运行密度大及地震带分布范围广,使得我国高速铁路桥梁面临巨大的潜在地震威胁。目前地震下的高速铁路桥梁及桥上行车安全相关规定不够详细具体,地震下安全防控尚未将列车、轨道、桥梁作为一个大系统进行安全设防,亟待开展系统研究保障地震下高速铁路桥梁结构及桥上行车安全。针对高速铁路轨道 桥梁系统结构特性,首先介绍地震作用下高速铁路轨道 桥梁系统破坏特征和损伤机理研究现状,然后从震后高速铁路桥上轨道不平顺状态劣化机理、地震作用下高速铁路列车 轨道 桥梁系统动力分析、地震作用后桥上行车安全分析及基于性能的高速铁路桥梁抗震设计方法等几个方面阐述现有研究进展及现有研究的不足,最后针对地震下高速铁路列车 轨道 桥梁系统多状态多水准多防线安全防控急需开展系统研究的问题进行展望。     

Fatigue behavior and statistical evaluation of the stress category for a steel-concrete composite bridge deck

The maintenance cost of bridges is rapidly increasing since many existing bridges are deteriorating or reaching their design life all over the world. Moreover, as many long-span bridges are under construction and planning in Korea, research and development on bridge decks with high load-resistance capacity as well as high fatigue strength has become a growing concern. This research gives experimental results of the fatigue behavior of a new-type of steel-concrete composite bridge deck being developed under such circumstances. The proposed composite bridge deck consists of corrugated steel plate, welded steel ribs, stud shear connectors, and reinforced concrete filler. Fatigue tests were conducted under a four-point bending test with four different stress ranges in constant amplitude. In order to determine the influence of the concrete filling, fatigue tests on partial steel specimens containing only plain corrugated steel plates were performed in advance. The partial steel specimens and the steel-concrete composite deck specimens both showed fatigue failure in the tension part concerning the fillet welding part between the corrugated steel plate and steel rib. Finally, the stress category of the fillet welding part of each specimen is evaluated based on a statistical approach of Albrecht’s probability model. The research concludes that the fatigue behavior of such steel-concrete composite decks under sagging moment can be estimated based on the classical S-N approach, focusing on steel components.     

Extending the lifetime of steel truss bridges by cost-efficient strengthening interventions

Abstract

The large number of existing bridges and viaducts all around the country has become a major problem for bridge owners. In the specific case of steel truss bridges, a reasonable method to extend the lifetime of existing structures is represented by the introduction of new deck systems combined with diffused strengthening interventions. In this study, a stepwise approach considering different loading conditions is presented (historical and Eurocode loads). The structural analysis has been performed on a case study bridge with a finite element model (FEM) calibrated on load tests. It was found that the predicted deformation agreed reasonably with the experimental results. Different strengthening alternatives were analysed and discussed: the introduction of orthotropic deck; the construction of composite deck with differentiating thickness and ordinary concrete strength; the construction of composite deck with differentiating thickness and high concrete strength; in some cases, also steel-to-steel interventions on the bridge are provided. It has been found that the best structural strengthening alternative lies in the construction of a composite concrete or of an ultra high-performance concrete (UHPC) or an ultra high-performance fibre-reinforced concrete (UHPFRC) deck with a reduced thickness (compared with traditional interventions) resting on the existing steel structure combined with steel-to-steel interventions.     

State-of-the-art of long-span bridge engineering in China

This paper introduces the state-of-the-art of longspan bridge engineering in China with emphases on recent long-span bridge projects, bridge deck configuration and material, design codes of long-span bridges and improvement of aerodynamic performance. The recent long-span bridge projects include thirty-eight completed suspension bridges, cable-stayed and arch bridges with a main span over 400 m, and eighteen major bridges are under construction. The bridge deck configuration and material, with prestressed concrete decks, steel-concrete composite decks and steel box decks together with several popular cross-sections, are presented. The third part briefly outlines four design codes, including static and dynamic design for highway long-span bridges, and the recent engineering experiences gained from several aerodynamic vibration control projects of long-span bridges are shared in the last part.     

分离式公铁双层桥面桥梁-列车-风屏障系统气动效应风洞试验研究

为探究侧风作用下分离式公铁双层桥面桥梁上、下桥面间气动干扰效应对列车气动效应的影响,在无风屏障和设置风屏障两种情况下,分别针对单独铁路桥和标准间隔高度下的公铁双层桥面桥梁,通过大比例尺节段模型风洞试验测试了列车的气动力系数以及铁路桥面轨道上方的风速剖面变化规律。为了进一步探究公铁双层桥面间隔高度对列车气动效应的影响,测试了多种间隔高度下列车气动力系数以及铁路桥面轨道上方的风速剖面变化规律。结果表明,公铁双层桥面间气动干扰效应对列车气动效应有一定的影响,间隔高度的改变会引起铁路桥面风速剖面以及列车气动力系数的变化,对比分析可知,无风屏障时间隔高度仅需满足铁路桥梁基本建筑限界即可,设置风屏障后,当间隔高度≥15m时,铁路桥面风速剖面以及迎风侧轨道处列车气动力变化趋于平缓。