Remaining fatigue life of steel railway bridges under enhanced axle loads

In this study, various fatigue damage models proposed by researchers have been briefly discussed and found that the models are problem specific and their efficacy needs to be checked for high cyclic fatigue cases such as in railway bridges. Towards this, field studies were conducted to obtain the strain responses from a steel bridge during the passage of scheduled trains and test train formation with enhanced axle loading. Instrumentation was carried out at critical locations to obtain the responses from the girder. Three different scenarios have been considered to avoid the influence of noise. Further, numerical simulation of the bridge subjected to train loading at different speeds was carried out using ANSYS to obtain synthetic data of strain response from the validated finite element model. Analysis was carried out for normal as well as for futuristic speed of the trains. Responses obtained from field measurements as well as from numerical investigations were used to calculate the damage indices. Based on the damage indices, remaining fatigue life of the bridge was evaluated. The present study can be helpful in assessing the health condition of the railway bridges and to check the suitability of further increase in axle load or speed of trains.     

Ganzheitliche Analyse von Stahl‐ und Verbundeisenbahnbrücken

Holistic analysis on steel‐ and composite railway bridges – Innovative solutions for strengthening durability and reducing construction times (Part 1). Investigations on sustainability on infrastructure projects differ from comparable investigations on building constructions through their longer life‐cycle of the objects. Questions regarding sustainability are thus accompanied by questions of durability and simple, mostly undisturbed maintenance through the whole life‐cycle. By the application of innovative railway bridges with steel and composite constructions blocking times induced by the construction time and maintenance actions within the usage phase, can be effectively reduced. Additionally the optimization of restrictive fatigue‐details can affect the whole life‐cycle of a bridge‐construction. In the frame of the FOSTA‐AiF‐research project „Holistic Assessment of steel‐ and composite railway bridges according to criteria of sustainability“ different innovative railway bridge types have been compared to their corresponding conventional bridge types and evaluated over their whole life‐cycle to quantify their advantageousness. While this article shows the investigated innovative bridge‐variants in constructive regards and optimization proposals and design approaches are explained, the second article is about the holistic approach and the results of the sustainability assessment of the investigated steel‐and composite railway bridge.     

Versuche an genieteten Brückenlängsträgern – Statisches Verhalten,Ermüdungsfestigkeit und Rissausbreitung

Tests on riveted bridge stringers – behaviour under static loads, fatigue strength and crack propagation. The assessment of the load‐carrying capacity and of the remaining fatigue life of existing railway and road bridges has gained an increasingly significant role over the last years. Thus, the problem of determining adequate strength values of riveted members of older steel bridges once again arose during the elaboration of the ONR 24008 specification. In the course of a research project initiated by the Austrian Federal Railways (ÖBB), static and fatigue tests were carried out on riveted members taken from a demolished railway bridge in Salzburg. The results of these tests gave further insight into the load carrying behaviour of built‐up riveted members, particulaly the progagation of fatigue cracks.     

Schweißen ermüdungsbeanspruchter Altstahlkonstruktionen – Untersuchungen zum Einfluss der Vorbelastung auf die Lebensdauer der Schweißkerbdetails

Welding of existing steel structures – Effect of prior load cycles. When existing structures under fatigue load are to be strengthened or refurbished by welded joints fatigue assessment is required for new welds. For the analysis of existing structures or determining of their remaining fatigue life, experimental investigations were carried out in order to estimate the effect of prior load cycles on the material. Mild steel specimens were preloaded cyclically, then surface treatment was applied and a notch representative for a real weld of a structure was introduced. The results of fatigue tests were compared with fatigue tests on similar non‐preloaded specimens. It has been found that there is no significant effect of prior load cycles if the surface is treated prior to welding and enough fusion penetration depth is given. Therefore, fatigue assessment of new welds on old materials does not need to take into account prior load cycles.     

铁路钢桥基于名义应力法的疲劳寿命预测研究

通过建立铁路疲劳列车模型,采用自编的影响线动态加载程序和三点雨流计数法程序对某64m钢桁梁桥不同部位杆件的应力谱进行了计算分析,并对其疲劳寿命预测进行了研究,得出了一些重要结论,可为铁路钢桥的疲劳寿命预测提供理论依据。     

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.     

不锈钢复合钢板在铁路钢桥上的应用技术

我国高速铁路钢桥均采用正交异性板钢桥面有碴线路。为提高钢桥面的防腐与使用寿命,合肥铁路枢纽南环线钢桁梁的桥面板采用了具有较高的强度、塑性、韧性、疲劳性能及优良抗腐蚀性能的321-Q345q-D不锈钢复合钢板。针对钢桥面系结构设计特点及制作与安装工艺需要,依据TB10212-2009《铁路钢桥制造规范》、GB/T13148-2008《不锈钢复合钢板焊接技术要求》,对321-Q345q-D不锈钢复合钢板进行焊接工艺试验,其试验结果(数据)均满足设计与施工要求。经对不锈钢复合钢板的钢桥面制作与安装实践,对铁路钢桥推广应用不锈钢复合钢板提出改进建议。     

Prediction of fatigue crack growth in steel bridge components using acoustic emission

The correlation of acoustic emission (AE) signal characteristics with crack growth behavior is of paramount importance to structural health monitoring and prognosis for in-service steel bridges. Relationships between AE absolute energy rate and crack growth rate are developed and presented. The relationships are based on experimental investigations intended to represent conditions found for in-service steel bridges. The approach presented is independent of the stress intensity range, which may simplify the life prediction procedure because stress intensity range is not always well defined in actual bridge components. Fatigue tests were performed to detect AE signals from fatigue cracks using compact tension (CT) specimens made of ASTM A572G50. Noise induced AE signals were filtered through a combined approach involving Swansong II Filters and investigation of waveforms, which are appropriate for data filtering and interpretation of field tests. Based on the experimental data and presented model, procedures for predicting crack extension and remaining fatigue life were carried out. Agreement between the predicted cracks and actual cracks verified the presented model and procedure. The study indicates that AE absolute energy rate may be more suitable than count rate in fatigue life prediction for the material of interest.     

铁路大跨度钢管混凝土拱桥拱肋管节点的疲劳性能研究

在研究大量资料文献的基础上,结合空间有限元分析,对比各种管节点疲劳检算方法的优缺点,研究了空心管节点疲劳检算方法在填心钢管-空心钢管节点疲劳性能分析中的适用性,对我国某在建大跨度铁路钢管混凝土拱桥(Y桥)拱肋管节点的疲劳性能作了可靠的分析评估,根据分析结果对该桥拱肋管节点的疲劳设计提出了合理建议。     

Ermüdungsbeanspruchungen von Betonbrücken unter zunehmendem Schwerverkehr

Fatigue Life of Concrete Bridges under Consideration of Increasing Traffic Loads Increasing traffic loads lead to higher fatigue stresses on bridge structures. The effects on the stresses of the main load‐bearing structure depend on the load models representing weight and the ratio of the load model length to the bearing distance of the superstructure. Within a research project carried out on behalf of the Federal Ministry of Transport, Building and Urban Affairs several different bridge constructions (box girder bridge, skew slab construction, girder bridge with T‐beam elements) were analysed with respect to their fatigue strength. Hence, the stresses in concrete and steel components are examined on extensive numerical models in longitudinal and transversal direction. The fatigue investigations of these existing bridges are performed by specified load combinations according to the German Standard for the design of concrete bridges. Furthermore the future development of heavy traffic loads is included by calculating the effects of a 60to‐heavy traffic vehicle.     

Instandsetzung und Verstärkung von Stahlbrücken mit Kategorie‐3‐Schäden

Reinforcing steel bridges with category 3 damages – report on a BASt research project. In recent years, fatigue damages have been observed at the main supporting structure of steel bridges, the orthotropic decks, as well as the transverse structure of steel bridges (the so‐called category 3‐failure). The rapidly increasing road traffic intensifies the situation resulting in a huge amount of steel bridges affected by fatigue damages. Existing steel bridges with category 3‐fatigue cracks have been intensively investigated. Fatigue failure modes and general evaluation criteria have been summarized, analysed and categorized, in order to enable first fundamental and time‐efficient definition and classification of category 3‐damages. FE‐simulations of transversal steel bridge structures (with and without reinforcements) have been carried out to evaluate and review the structural bridge concepts. Based on these studies, a special way of the steel bridges' maintenance has been followed up, which is removing all possible transversal bracings. Finally, different options of maintenance and repair have been investigated both newly and successfully applied in the recent past. Appropriate actions for solving essential category 3‐fatigue problems are presented.     

钢管桁架结构铸钢焊接节点疲劳性能研究进展

空间钢管桁架经常需要采用铸钢件来解决复杂节点的焊接问题。在桥梁、海洋石油平台、风力发动机塔架等疲劳荷载起控制作用的结构中,铸钢件-热轧钢管之间的焊接疲劳性能是需要特别关注的问题。详细介绍国际上铸钢焊接节点在工程的应用、铸钢件材料以及与钢管焊接节点的疲劳性能的研究进展,对一些相关问题进行讨论,指出铸钢焊接节点需要进一步研究的疲劳问题,以期促进我国铸钢焊接节点的工程应用和设计。     

Assessment procedure and rehabilitation criteria for the riveted railway Adige Bridge

Traffic patterns increasing and the degradation of existing railway steel bridges has lead to the need of an assessment of their remaining fatigue life, and deciding whether to retrofit or supply structure replacement. This paper deals with the structural assessment of an actual case study, the Adige Bridge, which connects the Rovigo and Padua provinces in northern Italy. The bridge has been in service since 1886 and the overall length is about 161m through three spans. As a reference the innovative procedures to estimate the remaining fatigue life of bridges outlined in the JRC-ECCS document Assessment of Existing Steel Structures: Recommendations for Estimation of Remaining Fatigue Life, has been applied for the case study, together with other codes and technical instructions. Stress data, obtained by a 3D finite element model, were used to estimate the remaining fatigue life. Assessment results, obtained by considering different traffic estimations, point out that most of the identified critical details have an infinite remaining safe life, but at the same time some members appear critical. Appropriate retrofitting criteria are proposed to support the designer in common damage situations.     

Fatigue assessment and strengthening measures to upgrade a steel railway bridge

The present paper deals with the experimental and analytical study of a 19th century riveted steel truss railway bridge to assess its current condition and remaining time of life. The analysis includes static and dynamic field measurements and laboratory tests. The evaluation of the capacity of the bridge for the trainloads, as well as for the seismic and wind loads, as specified by current design codes, was performed using a finite element model. Besides, after the owner's recent decision to upgrade the bridge to meet modern standards and new types of trains, the necessary strengthening was proposed, and the new estimation of the remaining fatigue life of the bridge after the suggested strengthening was also provided.     

Application of new damage indicator-based sequential law for remaining fatigue life estimation of railway bridges

Miner’s rule is generally accepted as the fatigue criteria for life estimation of railway bridges. Similarly, it has always been acknowledged as a simplification that is easy to use in design where detailed loading history is unknown. But in the case of existing railway bridges where the detailed loading history is known, Miner’s rule might provide incorrect results because of its omission of load sequence effect. Recently, a new damage indicator-based sequential law has been proposed to capture the load sequence effect more precisely. However, application of this sequential law to estimate the remaining fatigue lives of existing railway bridges has not been properly studied. Therefore, the major objective of this paper is to estimate the remaining fatigue life of a railway bridge using the sequential law and hence introduces a new approach to estimate remaining fatigue life of riveted railway bridges. This approach is specially based on combination of real stress histories, sequential law and fully known Wöhler curve. The practice of sequential law to obtain the remaining fatigue lives due to both uniaxial and multiaxial stresses are described by estimating remaining life of a considered railway bridge. Further, the obtained fatigue lives are compared with Miner’s estimations. Hence it could be concluded that it is advisable to apply the sequential law for assessment of remaining fatigue lives of riveted railway bridges, where the detailed stress histories are known.     

Fatigue tests on riveted steel elements taken from a railway bridge

Assessment of structural integrity and remaining life are essential tools for the management of ageing infrastructures, especially bridges. Compared to bolted or welded structures, little attention has been devoted to the fatigue assessment of riveted details. To fill this gap, extensive experiments are conducted on a short-span two-lane riveted steel-girder railway bridge near Sacile, Italy. In service since 1918, it was dismantled in 2006 and moved to a structural laboratory. Within a fatigue assessment framework, first physical and physical–chemical tests were performed, characterising the material properties; then, static, cyclic and fatigue full-scale tests were carried out. The experimental investigation allowed to test in particular the safe condition of the short riveted diaphragm connections of the bridge, and to compare the current fatigue design curves with experimental results. Moreover, the current practice to equate the fatigue behaviour of rivets to that of non-preloaded bolts proved to be a safe comparison.     

Performance of strengthened hybrid structures renovated from old railway steel bridges

Structural repair or maintenance technique has been a hot issue in recent years due to the increasing aging problems of old railway bridges, which have been used beyond or approaching their design service life. A strengthening method for old steel railway bridges by integrating the new structural members was adopted in engineering practice in this context. Rubber–latex mortar, GFRP plates and rapid hardening concrete were integrated with the old steel railway bridge to increase its rigidity and reduce both stress levels and structure-borne sound levels of the old steel bridge. The purpose of the present study is to investigate the mechanical performance of the renovated hybrid railway bridge. The material test on aged structural steel, the static loading test on the strengthened bridge, and the impact hammer test on the old bridge before and after strengthening, were performed to confirm the effects of present strengthening method. Moreover, three-dimensional FE models were built to make a comparison study between the strengthened and the original steel bridge. Both experimental and numerical results indicate that the renovation method can greatly enhance the stiffness and reduce the stress levels of steel members, resulting in the extension of the service life of the old steel railway bridge. Furthermore, noise reduction effects by using concrete and rubber–latex mortar were confirmed in the impact test.     

杭州湾观光塔铸钢节点疲劳性能试验研究

杭州湾跨海大桥观光塔处于近海,结构受到海洋波浪荷载的作用,需对塔中2个铸钢节点的疲劳性能进行试验研究。通过对塔中的2个铸钢上节点模型(缩尺比例为1∶4)的静载试验和抗弯疲劳试验,研究了GS-20Mn5V的铸钢节点的疲劳性能。试件在3种循环荷载作用下的滞回曲线的变化和应变随着循环次数的增加而降低的规律表明,GS-20Mn5V铸钢属于应力强化材料。分析试件在不同应力幅作用下的疲劳寿命变化,得到了GS-20Mn5V铸钢节点的疲劳极限及S-N曲线。研究结果表明,观光塔中的铸钢节点在波浪荷载作用下能够保证结构安全。     

高强度钢材疲劳性能研究进展

疲劳破坏是钢结构失效的主要形式,也是工程界与学术界关注的重点。在总结了国内外高强钢母材、焊缝连接和螺栓连接的疲劳性能研究现状基础上,介绍了疲劳寿命理论计算方法,结合大量试验数据分析统计了高强度钢材疲劳寿命发展规律,并基于国内外不同的疲劳设计规范对高强钢母材及连接接头的抗疲劳能力进行了评估。结果表明：随着钢材强度等级的提高,高强钢母材表现出较好的疲劳性能,规范设计曲线偏于保守,明显低估了高强钢母材的抗疲劳性能;受焊接工艺和焊接质量影响,高强钢焊缝连接的疲劳强度提高幅度较小,ANSI/AISC 360-10和EN 1993-1-9规范曲线能够较好地评估Q460D与Q690D焊缝连接的疲劳特性,并具有足够的安全储备;螺栓连接的疲劳强度受预紧力、摩擦面处理、成孔方式等众多因素影响,已有研究表明随着钢材强度的提高,疲劳强度亦有改善,ANSI/AISC 360-10和BS 7608-2014设计曲线适用于Q460螺栓连接疲劳寿命计算,具有足够安全保障,对于Q690钢螺栓连接疲劳性能评估,规范方法偏于保守。随着高强度钢材在实际工程中的应用增多,需开展大量不同等级高强钢母材和连接形式的疲劳试验,补充Q460及以上强度钢材的疲劳设计方法和细部连接构造。     

基于断裂力学模型对铆接铁桥剩余寿命的评估

以某黄河铁桥为例,结合有限元分析,介绍了基于断裂力学的既有铆接铁路钢桥剩余寿命评估的原理和方法,克服了传统疲劳评估方法中存在的不足,提出了该桁架剩余寿命评估结果。