The work presented in this thesis studies the load and loadeffects of traffic loads on railway bridges. The increasedknowledge of the traffic loads, simulated using fieldmeasurements of actual trains, are employed in a reliabilityanalysis in an attempt at upgrading existing railwaybridges. The study utilises data from a weigh-in-motion site whichrecords, for each train, the train speed, the loads from eachaxle and the axle spacings. This data of actual trainconfigurations and axle loads are portrayed as moving forcesand then used in computer simulations of trains crossing twodimensional simply supported bridges at constant speed. Onlysingle track short to medium span bridges are considered in thethesis. The studied load effect is the moment at mid-span. Fromthe computer simulations the moment history at mid-span isobtained. The load effects are analysed by two methods, the first isthe classical extreme value theory where the load effect ismodelled by the family of distributions called the generalisedextreme value distribution (GEV). The other method adopts thepeaks-over-threshold method (POT) where the limiting family ofdistributions for the heights to peaks-over-threshold is theGeneralised Pareto Distribution (GPD). The two models aregenerally found to be a good representation of the data. The load effects modelled by either the GEV or the GPD arethen incorporated into a reliability analysis in order to studythe possibility of raising allowable axle loads on existingSwedish railway bridges. The results of the reliabilityanalysis show that they are sensitive to the estimation of theshape parameter of the GEV or the GPD. While the study is limited to the case of the ultimate limitstate where the effects of fatigue are not accounted for, thefindings show that for the studied cases an increase inallowable axle load to 25 tonnes would be acceptable even forbridges built to the standards of 1940 and designed to LoadModel A of that standard. Even an increase to both 27.5 and 30tonnes appears to be possible for certain cases. It is alsoobserved that the short span bridges ofapproximately fourmetres are the most susceptible to a proposed increase inpermissible axle load. <b>Keywords:</b>bridge, rail, traffic load, load effect,dynamic amplification factor, extreme value theory,peaks-over-threshold, reliability theory, axle loads, fielddata.

<p>The work presented in this thesis studies the load and loadeffects of traffic loads on railway bridges. The increasedknowledge of the traffic loads, simulated using fieldmeasurements of actual trains, are employed in a reliabilityanalysis in an attempt at upgrading existing railwaybridges.</p><p>The study utilises data from a weigh-in-motion site whichrecords, for each train, the train speed, the loads from eachaxle and the axle spacings. This data of actual trainconfigurations and axle loads are portrayed as moving forcesand then used in computer simulations of trains crossing twodimensional simply supported bridges at constant speed. Onlysingle track short to medium span bridges are considered in thethesis. The studied load effect is the moment at mid-span. Fromthe computer simulations the moment history at mid-span isobtained.</p><p>The load effects are analysed by two methods, the first isthe classical extreme value theory where the load effect ismodelled by the family of distributions called the generalisedextreme value distribution (GEV). The other method adopts thepeaks-over-threshold method (POT) where the limiting family ofdistributions for the heights to peaks-over-threshold is theGeneralised Pareto Distribution (GPD). The two models aregenerally found to be a good representation of the data.</p><p>The load effects modelled by either the GEV or the GPD arethen incorporated into a reliability analysis in order to studythe possibility of raising allowable axle loads on existingSwedish railway bridges. The results of the reliabilityanalysis show that they are sensitive to the estimation of theshape parameter of the GEV or the GPD.</p><p>While the study is limited to the case of the ultimate limitstate where the effects of fatigue are not accounted for, thefindings show that for the studied cases an increase inallowable axle load to 25 tonnes would be acceptable even forbridges built to the standards of 1940 and designed to LoadModel A of that standard. Even an increase to both 27.5 and 30tonnes appears to be possible for certain cases. It is alsoobserved that the short span bridges ofapproximately fourmetres are the most susceptible to a proposed increase inpermissible axle load.</p><p><b>Keywords:</b>bridge, rail, traffic load, load effect,dynamic amplification factor, extreme value theory,peaks-over-threshold, reliability theory, axle loads, fielddata.</p>

No description available.

An increase in the demand for the freight shipping in the United States has been predicted for the near future and Longer Combination Vehicles (LCVs), which can carry more loads in each trip, seem like a good solution for the problem. Currently, utilizing LCVs is not permitted in most states of the US and little research has been conducted on the effects of these heavy vehicles on the roads and bridges. In this research, efforts are made to study these effects by comparing the dynamic and fatigue effects of LCVs with more common trucks. Ten Steel and prestressed concrete bridges with span lengths ranging from 30’ to 140’ are designed and modeled using the grid system in MATLAB. Additionally, three more real bridges including two single span simply supported steel bridges and a three span continuous steel bridge are modeled using the same MATLAB code. The equations of motion of three LCVs as well as eight other trucks are derived and these vehicles are subjected to different road surface conditions and bumps on the roads and the designed and real bridges. By forming the bridge equations of motion using the mass, stiffness and damping matrices and considering the interaction between the truck and the bridge, the differential equations are solved using the ODE solver in MATLAB and the results of the forces in tires as well as the deflections and moments in the bridge members are obtained. The results of this study show that for most of the bridges, LCVs result in the smallest values of Dynamic Amplification Factor (DAF) whereas the Single Unit Trucks cause the highest values of DAF when traveling on the bridges. Also in most cases, the values of DAF are observed to be smaller than the 33% threshold suggested by the design code. Additionally, fatigue analysis of the bridges in this study confirms that by replacing the current truck traffic with higher capacity LCVs, in most cases, the remaining fatigue life of the bridge is only slightly decreased which means that taking advantage of these larger vehicles can be a viable option for decision makers.

No description available.

Due to the emergence of new materials and advanced engineering technology, slender footbridges are increasingly becoming popular to satisfy the modern transportation needs and the aesthetical requirements of society. These structures however are always &quotlively" with low stiffness, low mass, low damping and low natural frequencies. As a consequence, they are prone to vibration induced by human activities and can suffer severe vibration serviceability problems, particularly in the lateral direction. This phenomenon has been evidenced by the excessive lateral vibration of many footbridges worldwide such as the Millennium Bridge in London and the T-Bridge in Japan. Unfortunately, present bridge design codes worldwide do not provide sufficient guidelines and information to address such vibrations problems and to ensure safety and serviceability due to the lack of knowledge on the dynamic performance of such slender vibration sensitive bridge structures. A conceptual study has been carried out to comprehensively investigate the dynamic characteristics of slender suspension footbridges under human-induced dynamic loads and a footbridge model in full size with pre-tensioned reverse profiled cables in the vertical and horizontal planes has been proposed for this purpose. A similar physical suspension bridge model was designed and constructed in the laboratory, and experimental testings have been carried out to calibrate the computer simulations. The synchronous excitation induced by walking has been modelled as crowd walking dynamic loads which consist of dynamic vertical force, dynamic lateral force and static vertical force. The dynamic behaviour under synchronous excitation is simulated by resonant vibration at the pacing rate which coincides with a natural frequency of the footbridge structure. Two structural analysis software packages, Microstran and SAP2000 have been employed in the extensive numerical analysis. Research results show that the structural stiffness and vibration properties of suspension footbridges with pre-tensioned reverse profiled cables can be adjusted by choosing different structural parameters such as cable sag, cable section and pretensions in the reverse profiled cables. Slender suspension footbridges always have four main kinds of vibration modes: lateral, torsional, vertical and longitudinal modes. The lateral and torsional modes are often combined together and become two kinds of coupled modes: coupled lateral-torsional modes and coupled torsionallateral modes. Such kind of slender footbridges also have different dynamic performance in the lateral and vertical directions, and damping has only a small effect on the lateral vibration but significant effect on the vertical one. The fundamental coupled lateral-torsional mode and vertical mode are easily excited when crowd walking dynamic loads are distributed on full bridge deck. When the crowd walking dynamic loads are distributed eccentrically on half width of the deck, the fundamental coupled torsional-lateral mode can be excited and large lateral deflection can be induced. Higher order vertical modes and coupled lateral-torsional modes can also be excited by groups of walking pedestrians under certain conditions. It is found that the coupling coefficient introduced in this thesis to describe the coupling of a coupled mode, is an important factor which has significant effect on the lateral dynamic performance of slender suspension footbridges. The coupling coefficient, however, is influenced by many structural parameters such as cable configuration, cable section, cable sag, bridge span and pre-tensions, etc. In general, a large dynamic amplification factor is expected when the fundamental mode of a footbridge structure is the coupled lateral-torsional mode with a small coupling coefficient. The research findings of this thesis are useful in understanding the complex dynamic behaviour of slender and vibration sensitive suspension footbridges under humaninduced dynamic loads. They are also helpful in developing design guidance and techniques to improve the dynamic performance of such slender vibration sensitive footbridges and similar structures and hence to ensure their safety and serviceability.

No description available.

In this thesis a train-track-bridge interaction (TTBI) model is developed in order to study the dynamic amplification from track irregularities on railway bridges traversed by freight trains. These simulations are of great importance since rail freight transport is expected to increase in order to meet the climate goals. The shift of the freight industry is however not accomplished without complications, because of the heavier and more frequent transportation higher demand is put on the infrastructure supporting the railways. In order to adequately assess the bearing capacity of the railway bridges, more detailed models assessing the dynamic behavior of the bridges are needed. The research underlying the current model in Eurocode were made during the 1970s (ORE, 1976) and the 1990s (ERRI, 1999) which were based on very simplified relations of the interaction and irregularities. Two research questions are therefore established in this thesis. The first one is if the current dynamic amplification factor in Eurocode which accounts for track irregularities is over conservative and secondly if the same factor is suitable to utilize for both section forces and deflections. The model developed in order to answer the stated research questions is a 2D model (considering only vertical excitation) with a linearized Hertz contact spring coupling the vehicle subsystem to the track-bridge system. The bridges examined in the thesis are limited to simply supported bridges with a span length between 4-20 m carrying a ballasted track. The studied train speeds vary between 60 - 120 km/h in order to replicate the speed range utilized by freight trains. The quality of the track (irregularities) is varied between a standard variation of 0.5-5 mm and is generated based on the German power spectral density (PSD) function. Research have previously been carried out in the field of TTBI system but have mostly been focusing on high-speed railway engineering and few studies have been performed on heavy transportation. One of the pioneers in the field of TTBI modelling is Wanming Zhai and the model developed in this thesis is validated against one of his 2D models. Based on the simulations performed in this thesis it is evident that the current model in Eurocode EN 1991-2 is over conservative and in great need of a revision. The model presented in this thesis is for the case with the largest dynamic amplification (120 km/h and a 4 m span length) significantly lower than the model presented in Eurocode. From the sensitivity analysis it is possible to conclude that many of the parameters in the system have low influence on the dynamic amplification while others have considerable influence. The parameters that have a considerable influence might be more suitable with a probabilistic approach instead of a deterministic which was utilized in this thesis. / I denna avhandling upprättas en tåg-spår-bro interaktionsmodell i syfte att studera den dynamiska förstorningsfaktorn som uppkommer av ojämnheter från spåret för järnvägsbroar trafikerade av godståg. Dessa typer av simuleringar är viktiga då järnvägstransporter förväntas öka för att klara av att möta de klimatmål som fastställts. Denna ökning av järnvägstransporter genomförs dock inte utan problem. Ökningen medför fler och tyngre transporter vilket skapar problem för järnvägsinfrastrukturen (främst broarna). För att med säkerhet kunna fastställa bärförmågan hos broarna, behövs mer avancerade modeller än de som idag finns i Eurokod. Modellerna som finns angivna i Eurokod bygger på forskning genomförd under 70- (ORE, 1976) och 90-talet (ERRI, 1999), där det användes väldigt förenklade interaktions- och ojämnhets-modeller. På grund av detta har två frågeställningar upprättats. Den första är om den dynamiska förstoringsfaktorn som används i Eurokod för att ta hänsyn till ojämnheterna i spåret är överdrivet konservativ och den andra är om samma faktor är lämplig att använda för både snittkrafter och nedböjning. Modellen som upprättats för att besvara dessa forskningsfrågor är en 2D modell (vertikalt led) med en linjäriserad Hertz kontaktfjäder för att koppla samman fordonet med spår-bro systemet. Broarna som har studerats i denna avhandling är endast fritt upplagda broar med en spannlängd mellan 4-20 m med ballasterat spår. Tåg-hastigheten har varierats mellan 60-120 km/h i syfte att simulera relevanta hastigheter för godståg. Spårkvalitén (ojämnheterna) har beskrivits m.h.a. standardavvikelsen från det perfekta spårläget och har varierats mellan 0.5-5 mm. Dessa ojämnheter har genererats baserat på den tyska power spectral density (PSD) funktionen. Tidigare forskning har utförts inom ämnet tåg-spår-bro interaktion men med huvudsaklig fokus på höghastighetståg/resonans-beteenden och få studier har genomförts på godståg. En av föregångsmännen inom ämnet är Wanming Zhai, och modellen som upprättas i denna avhandling har därav validerats mot hans 2D modell. Baserat på simuleringarna i denna avhandling är det tydligt att den nuvarande modellen som används i Eurokod EN 1991-2 är överdrivet konservativ och i stort behov av en uppdatering. Det fall med stört dynamisk förstoringsfaktor (120 km/h och en spannlängd på 4 m) som behandlas i denna rapport är avsevärt lägre än det som återfinns i Eurokod. Från känslighetsanalysen som genomfördes kunde det fastställas att många av parametrarna i systemet har en låg inverkan på förstoringsfaktorn. För parametrarna som dock hade inflytande skulle ett probabilistiskt angreppssätt kunna vara mer passande än det deterministiska som använts i denna avhandling.