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  • 1. Cermona, Christian
    et al.
    Patron, Alberto
    Hoehler, Susan
    Eichler, Björn
    Johansson, Bernt
    Larsson, Tobias
    Improved assessment methods for static and fatigue resistance of old metal railway bridges2007Inngår i: Sustainable bridges: assessment for future traffic demands and longer lives / [ed] Jan Bien; Lennart Elfgren; Jan Olofsson, Wrocław: Dolnoslaskie Wydawnictwo Edukacyjne , 2007, s. 261-272Konferansepaper (Fagfellevurdert)
  • 2. Christian, Cremona
    et al.
    Johansson, Bernt
    Larsson, Tobias
    Patron, Alberto
    S, Hoehler
    B, Eichler
    Improved assessment methods for static and fatigue resistance of old metal railway bridges2008Inngår i: Bridge Maintenance, Safety Management, Health Monitoring and Informatics: Proceedings of the Fourth International Conference on Bridge Maintenance, Safety and Management, July 13-17 2008, Seoul, Korea - IABMAS '08, Boca Raton, Fla: Taylor and Francis Group , 2008, s. 3666-3674Konferansepaper (Fagfellevurdert)
  • 3.
    Cremona, Christian
    et al.
    Technical Department for Transport, Roads, Bridges and road Safety Bagneux Cedex.
    Eichler, Bjorn
    Johansson, Bernt
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Larsson, Tobias
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Improved assessment methods for static and fatigue resistance of old metallic railway bridges2013Inngår i: Journal of Bridge Engineering, ISSN 1084-0702, E-ISSN 1943-5592, Vol. 18, nr 11, s. 1164-1173Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A large number of the bridges in the European railway networks are metallic bridges. The increasing volume of traffic and axle weight of trains mean that for many structures the loads today are much higher than those envisaged when they were designed. This paper presents a summary of the different recommendations and advices proposed in "Guidelines for Load and Resistance Assessment of Existing European Railway Bridges" of the European Union founded project "Sustainable bridges" for assessing old metal railway bridges. The knowledge of the material properties of existing metal bridges is essential for the resistance assessment and the determination of the remaining lifetime of old metallic bridges. Furthermore, old bridges require more exact and efficient assessment methods that call for a precise description of the material. Among the problems met in metal bridges and material properties estimation, fatigue is the most common cause of failure. To be able to make accurate assessments of existing bridges, it is important to know the behaviour of bridges exposed to fatigue, and how the old materials behave due to cyclic exposure. The main question answered herein is how to make a safe estimation concerning the remaining life in service. The possible traffic load on steel rail bridges is usually limited by the fatigue resistance, but for certain situations the static resistance has also to be checked. Most design rules for steel structures, for instance those in Eurocode 3, are applicable also to riveted structures. However, some information is missing on how to deal with the special case that elements are intermittently connected in contrast welded structures that are connected continuously. As the traditional methods for assessing the resistance of steel bridges are based on elastic analysis, a method for utilizing a limited redistribution of bending moments based on beam theory is proposed.

  • 4. Enochsson, Ola
    et al.
    Larsson, Tobias
    Elfgren, Lennart
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Kronborg, Anders
    Banverket.
    Paulsson, Björn
    Banverket.
    Dynamic amplification factors for a riveted steel bridge: assessment by monitoring of the Keräsjokk bridge in northern Sweden2007Inngår i: Sustainable bridges: assessment for future traffic demands and longer lives / [ed] Jan Bień; Lennart Elfgren; Jan Olofsson, Wrocław: Dolnoslaskie Wydawnictwo Edukacyjne , 2007, s. 435-444Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Measurements were carried out in order to improve an assessment of a riveted steel bridge from 1911. Dynamic Amplification factors, DAF, were estimated for different parts of the bridge by measurements of deflections and strains for a train passing over the bridge with different speeds. The measured dynamic amplification factors were considerably lower than the corresponding ones calculated according to available codes. Due to this it was possible to increase the axle load on the bridge from 22.5 to 25 tons.

  • 5. Larsson, Tobias
    Fatigue assessment of riveted bridges2009Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    The majority of the railways used today were built in the beginning of the 20th century. Most of the bridges constructed at that time are still in service. This was achieved by designing the bridges with an over capacity, this extra reserve in the design of the bridges was done since the axle load of trains and locomotives were changed during this period. To ensure that the bridge stock could manage future axle load alterations a buffer was assigned to their resistance.The situation with an increasing number of old bridges still in service that are reaching their design service life is similar in all of Europe, and because of their quantity it is impossible to replace all bridges at the same time.To be able to make old bridges stay in service longer enhancement of the existing assessment methods has to be made. To do this the procedure of an assessment must be known to be able to recognize where improvements can be made and areas that are critical in a bridge must be identified.This thesis has focused on the material properties of steel bridges constructed before the 1940's and how to estimate the remaining fatigue life of riveted bridges.By gathering information from bridges where the material properties have been determined a data base was created. From the information in the data base a better prediction concerning the properties to expect in steel bridges constructed before the 1940's is obtained. By using information from the data base a more accurate calculation of the resistance can be achieved which opens for the possibilities for higher loads to be allowed.Concerning the fatigue life of riveted bridges this thesis has focused on two areas. The first area is the girders of the secondary structure, stringers and cross girders, transferring loads from trains or cars to the main girders of the bridge. These girders are often in focus in assessments, due to their length and position in the bridge that makes them more exposed to fatigue damage than other parts. The work has focused on determining which detail category that should be used in calculations of the fatigue life for riveted structures. A survey was performed containing information of large scale fatigue tests performed on riveted bridge girders taken out from service and tests on small scale specimens to investigate influencing factors of the fatigue life.The second area concerning fatigue and how to estimate remaining time in service is the connections between the stringers and cross girders. The connections between these girders are often exposed to unintended load exposure causing cracking in these joints. A fracture mechanic approach was used to estimate the degradation of stiffness in these connections and the propagation rates of cracks. Also investigations were carried out concerning the best way of modelling these connections by comparing the results from the FEanalyses to field measurements.

  • 6. Larsson, Tobias
    Material and fatigue properties of old metal bridges2006Licentiatavhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    This thesis aims to answer questions regarding material and fatigue properties of bridges built between the end of the 19th century to 1940's. Regarding material properties the study involves the creation of a data base consisting of material properties of bridges. The establishment of a data base was done by retrieval of test certificates from material investigations conducted on existing bridges. The bridges in question were road and railway bridges produced before 1940's. The aim of the investigation was to determine the material properties of bridges in the specified interval and compare these with properties in evaluation codes. From the evaluation of the data base it became apparent that the yield strength of the existing bridges was higher than specified in the evaluations codes of Sweden and Denmark. Also a big divergence regarding the toughness properties were established for the investigated bridges. Regarding fatigue endurance, a literature survey of fatigue tests performed on riveted structures were conducted. The survey concerned both full scale structures retrieved from bridges taken out of service and small scale tests. The objective was to investigate the fatigue resistance of riveted structures. Factors as hole preparation, corrosion, clamping force and influence from materials properties on the fatigue performance was also inquired. In the evaluation of the fatigue tests it was concluded that fatigue endurance of riveted assembled girders was best described by the detail category C=63.

  • 7. Larsson, Tobias
    et al.
    Lagerqvist, Ove
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Byggkonstruktion och -produktion.
    Fatigue of riveted metal structures2008Inngår i: Bridge Maintenance, Safety Management, Health Monitoring and Informatics: Proceedings of the Fourth International Conference on Bridge Maintenance, Safety and Management, July 13-17 2008, Seoul, Korea - IABMAS '08 / [ed] Hyun-Moo Koh; Dan M. Frangopol, Boca Raton, Fla: Taylor and Francis Group , 2008, s. 1254-1261Konferansepaper (Fagfellevurdert)
  • 8.
    Patrón, A.
    et al.
    Laboratoire Central des Ponts et Chaussées, France.
    Cremona, C.
    Laboratoire Central des Ponts et Chaussées, France.
    Hoehler, S.
    RWTH Institute of Steel Construction, Aachen.
    Johansson, Bernt
    Larsson, Tobias
    Maksymowicz, M.
    Universidade do Minho.
    Improved assessment methods for static and fatigue resistance of metallic railway bridges in Europe2006Inngår i: Bridge maintenance, safety, management, life-cycle performance and cost: proceedings of the Third International Conference on Bridge Maintenance, Safety and Management, Porto, Portugal, 16 - 19 July 2006 / [ed] Paulo J. S. Cruz; Dan M. Frangopol, London: Taylor & Francis Group, 2006, s. 751-753Konferansepaper (Annet vitenskapelig)
    Abstract [en]

    A very important part of the bridges in the European railway networks are metallic bridges that have been built during the last 100 years (some of them are much older). The increasing volume of traffic and axle weight of trains means that for many structures the loads today are much higher than those envisaged when they were designed. This paper deals with the research program established to develop improved assessment methods for existing metallic bridges in the context of the work package 4 (Loads, Capacity and Resistance) of the 6th framework European project Sustainable Bridges. Three main research topics under development. The first topic concerns information about material properties of steel and iron used in old existing railway bridges. Any safety assessment for an old bridge requires the knowledge of the structural resistance and therefore the information of the material properties. For the resistance to static loads the material strength expressed as yield strength (fy) is the significant parameter. In order to ensure sufficient fatigue resistance, next to the classic fatigue methods using damage accumulation further assessment models have been established that are based on fracture mechanics. For the classic fatigue assessment the fatigue properties are needed. Fracture mechanical approaches, taking into account that crack-like defects are very likely to be in the structure, use the fracture toughness as material resistance. This is usually given by J-Integrals (Ji, Jc) or stress-intensity-factors (KIc). Also further crack growth parameters, e.g. threshold values for crack growth, are important. The early metal bridges in the 19th century were fabricated of cast iron or puddle iron (wrought iron). Puddle iron surpassed cast iron having a lower carbon content that goes along with a better ductility and it allowed forging and an easier workmanship. Yet at the beginning of the 20th century puddle iron was superseded by mild steels that obtained higher qualities concerning the chemical composition and cleanness as well as better technological material properties (e.g. weldability, strength). For these old metal bridges, that were built between 1870 and 1940 in particular, the material parameters are in many cases not available. One reason is that although steel production and construction technology (bolting and welding of joints) developed quickly, appropriate testing methods to examine relevant properties as toughness, fatigue, etc., were missing completely and were not available until many decades later. Therefore only fragmentary knowledge exists concerning early iron materials, complicating the handling and assessment of old metal structures. Therefore this research activity is based on the collection of material data from more than 120 old bridges from Sweden, France and Germany. The second topic is associated with the development of new assessment methods for resistance of riveted structures. This mainly concerns the study of resistance and deformation capacity of cross sections formed by riveted slender plates. Modern standards for design of steel structures like Eurocode 3 cover riveted structures but they do not give complete information. Old design standards on the other hand are quite incomplete concerning instability phenomena and they cover elastic design only. In this research Eurocode 3 is considered as the starting point and some additional information relevant for riveted structures will be developed. The cross section classes in Eurocode 3 are essential in defining the resistance to bending moment. They are defined for rolled or welded sections but those definitions are not sufficient for riveted girders. First the maximum distance between rivets in the stress direction has to be defined. Further, there are some beneficial effects of confinement of plates in certain cases. The traditional method for assessing the resistance of steel bridges is based on elastic analysis. In case the resistance in ULS is insufficient it is possible that allowing for plastic deformations gives a more favourable answer. This is very obvious if the girders are stocky enough for using plastic hinge analysis. This is rarely the case but also more slender girders have some plastic deformation capacity, which can be utilized for a limited redistribution of moments in the girders. The third research activity is related to the assessment of fatigue life of riveted and welded bridges. Fatigue related failures are the most common cause of failure of riveted bridges. Riveted structures were constructed over a period of more than 100 years up to the 1950s. A large number of riveted bridges (thousands) can be still found on the European railway networks. Constantly increasing loads and the fact that these bridges were not explicitly designed against fatigue raise questions regarding their remaining fatigue life. Economically its not justified to replace a bridge when it reaches the end of its design life. Often the design life it's an arbitrary value and there is considerable reserve. As is well known, metal fatigue exhibits high levels of uncertainty and can be influenced by a very important number of structure and environmental factors. An important amount of service life may be justified by a better knowledge of the fatigue behavior of riveted connections. Furthermore, the load history, which plays a main role in fatigue life evaluation, is largely unknown in most of cases. In that context, there appears to be a need to develop a comprehensive fatigue assessment methodology for riveted railway bridges. Since the 1950s welding become a useful procedure for assembling components of metallic bridges. In welded joints cracks are often localized at the welding. Indeed the welding process induce some defects which help small cracks to appear. These defects can growth under cyclical loading and can induce the joint failure, and depending of the redundancy degree of the bridge can lead to the failure of the structure. The conditions governing crack growth are respectively structural geometry, initiation site, material characteristics and loading. In general all these conditions are highly random. Therefore, an appropriate analysis of fatigue phenomena consists by treating the problem in a probabilistic manner. Fatigue durability and inspection planning are then very important issues in the design and scheduled inspection of welded bridges. Usually welded structures have to be designed for a finite life with an accepted probability of failure based on S-N approach. Consequently cracks may propagate and become critical during the estimated safe-life, unless detected in time and repaired. If fracture is not acceptable, supplementary safety measures must be taken through in-service inspection requirements specifying appropriated non-destructive inspection techniques (NDT) and inspection planning. This leads to the damage tolerance concept: a welded joint containing a crack has to resist the service loadings for some time. All through this time there must be a large probability that the crack can be detected (and repaired) before it becomes critical. In order to verify this probability, the reliability against such a failure have to be evaluated as a function of service time in support of inspection strategy. The fracture mechanics and the reliability theory provides the necessary tools for these calculations. This approach (so called probabilistic fracture mechanics) is used on the assessment of welded joints of metallic bridges. This kind of analysis is carried out using the first order reliability method (FORM) or Monte Carlo simulations, which have become the standard methods in structural reliability. A limit state is formulated by applying linear elastic fracture mechanics (LEFM) the uncertainties of the main parameters can be considered by treating them as basic random variables. One problem, which usually appears, is that the necessary statistical informations of these variables (mean value, standard deviation, and distribution type) are not known. Another problem is that this kind approach does not give the statistical distribution of the cumulated damage, or in different words, the statistical distribution of the crack sizes at a given time. This information is important to evaluate the performance of different NDT methods used to control welded joints in bridges. An alternative approach, based on concept of Markov chain is proposed.

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