A soil-steel composite bridge is a structure comprised of corrugated steel plates, which are joined with bolted connections, enclosed in friction soil material on both sides and on the top. The surrounding friction soil material, or backfill, is applied in sequential steps, each step involving compaction of the soil, which is a necessity for the construction to accumulate the required bearing capacity. Soil-steel composite bridges are an attractive option as compared with other more customary bridge types, owing to the lower construction time and building cost involved. This is particularly true in cases where gaps in the form of minor watercourses, roads or railways must be bridged.

The objective of this master thesis is the modelling of an existing soil-steel composite railway bridge in Märsta, Sweden with the finite element software Plaxis. A 3D model is created and calibrated for crown deflection against measurement data collected by the Division of Structural Engineering and Bridges of the Royal Institute of Technology (KTH) in Stockholm, Sweden.

Once the 3D model is calibrated for deflection, two 2D models with different properties are created in much the same way. In model 1, the full axle load is used and the soil stiffness varied, and in model 2 the soil stiffness acquired in the 3D model is used and the external load varied. The results are compared to measurement data. In 2D model 1 an efficient width of 1,46 m for the soil stiffness is used in combination with the full axle load, and in 2D model 2 an efficient width of 2,85 m is used for the external load, in combination with the soil stiffness acquired in the 3D model.

Aside from this, parametric studies are performed in order to analyse the effect of certain input parameters upon output results, and in order to analyse influence line lengths.

Recreating the accelerations and stresses in the existing bridge using finite element models is complicated, and the results reflect this. Below are shown the discrepancies between model results and measurement data for the pipe crown. The scatter in the measurement data has not been taken into consideration for this; these specific numbers are valid only for one particular train passage.

For crown deflection, the 3D model shows a discrepancy of 4%, 2D model 1 5% and 2D model 2 8% compared with measurement data. For crown acceleration, in the same order, the discrepancy with measurements is 1%, 71% and 21% for maximum acceleration, and 46%, 35% and 28% for minimum acceleration. For maximum crown tensile stress, the discrepancy is 95%, 263% and 13%. For maximum crown compressive stress, the discrepancy is 70%, 16% and 46%.

Structural steels are among the most widely used materials in the constructionsector, of which S355 is the steel that is considered being the norm in Europetoday. As the demands on civil engineering structures are increasing today parallelwith the construction sector intending to become a more environmentalfriendly industry, high strength steel (HSS) has become increasingly relevanttoday with the aim of reducing the material usage and facilitate a more sustainableconstruction. HSS is structural steel with a very high yield strength andultimate strength. In this dissertation, structural steels with a yield strengthof 500MPa or above were classified as HSS.In this thesis, the main steel girders of the E4 bridge over the Vapelbäcken,which is a continuous steel-concrete composite highway bridge, were optimizedwith HSS S690 and conventional structural steel S355 in order to investigatehow HSS affects the material usage for the bridge compared to the conventionalsteel. In addition to the above, a cost analysis, modal analysis and a fatigueassessment of bridge were carried out in order to analyse how the mass changedue to HSS affects the material cost of the bridge as well as the bridge’s dynamicproperties and fatigue resistance.The main girders of the bridge were optimized with respect to the ultimatelimit state (ULS). The optimization initiated with a structural analysis of thebridge using the finite element software Abaqus. Design calculations were thenperformed for the girders in accordance with the Eurocodes. Afterwards, thecross-sections of the main girders were optimized. When the optimization wascompleted, a cost analysis, modal analysis and the fatigue assessment wereperformed for the bridge.The optimization showed that HSS significantly reduces the material usagecompared to conventional steel if the optimization takes place with respect tothe ULS. The cost analysis showed that the bridge with optimized main girdersof HSS was the cheapest option, indicating that HSS can be a more economicalalternative than conventional structural steel if the material reduction is largeenough.The large material reduction that HSS entails led to deterioration of the bridge’sother properties. The modal analysis showed that the bridge with optimizedgirders of HSS was had the lowest natural frequency, indicating that the largemass reduction of the bridge due to HSS results in a impairing of the bridge’sdynamic properties since a large mass reduction impairs the stiffness of thestructure which in turn decreases the natural frequency. The fatigue assessmentshowed that the bridge with optimized girders of HSS had the lowestfatigue capacity, which means that the yield strength of the material does nothave an impact on the fatigue capacity and therefore the benefits of HSS cannotbe exploited in cases where fatigue governs the structural design.

In the year 2006, only 10 years after the steel- concrete composite bridge, Vårby bridge was built, fatigue cracks were found during an inspection. To further investigate the reasons and the potential danger of the cracks, an investigation under the commission of the Swedish Transport Administration was issued in 2009. After the detection of fatigue cracks, several measurements were carried out in order to monitor the static behavior by the use of strain gauges at selected positions along the bridge. The measurements from the strain gauges monitoring the global behavior were then used to calibrate an finite element model.

The present report is part of the research of understanding the behavior of steel-concrete composite bridges. Numerical analysis and model updating have been used in order to understand and determine how different parameters affects the strain range and the global behavior. The numerical analysis and parameter study were performed in the Finite Element software Abaqus and programming language Python. The outcome of the parameter study was then used to perform the model updating by the method of falsification in MATLAB.

The results from the parameter study and the model updating showed that the measured strains could be reached with a wide range of parameter combinations. Even with unreasonable parameter values, the measured strains were obtained. To investigate the reason for this, a multiple linear regression analysis was performed which showed that the strain range is strongly correlated to the Young’s modulus of steel and concrete and also to the connector elasticity, which resembles the studs in the real bridge.

Two different finite element models, with two completely different input parameter values, obtain the same strain range for the global behavior. It is therefore not certain to assume that a model is accurate and valid based on the fact that the predicted strain range from the finite element model is close to the measured strain range since the global behavior of a steel- concrete composite bridge can be modeled by many different sets of parameters.

In this paper, the spotlight is directed towards studying the handling capacity of pure Ro-Ro terminals, especially the new terminal of Norvik port. To this end, a simulation model based on a distributed architecture is built to assess the handling capacity under different flow scenarios with a particular focus on the trailer flow and export-lorry flow the terminal can handle in terms of resource availability, trailer-dwell times and management rules. This helped to determine the number of resources required to evacuate smoothly the incoming flows and to identify where potential bottlenecks happen the most inside the terminal. The established model is verified then validated by experts to conduct properly the experiment study where the model is fed with empirical data provided by terminal authorities. This experiment showed that the terminal can handle flows of which trailers do not exceed 17% and the export fraction of lorries is at most 42%.

Container terminals are complex systems where containerized cargo undergoes a set of processing and handling operations to be delivered to their outgoing modes. A pool of decision support methods and simulation models has been developed to assist planners and managers in making decisions about daily operations. Nevertheless, most are designed for a particular terminal and not generic types. Indeed, a generic model serves as a conceptual factory to create specific models which greatly reduces the time and efforts of development; however, building such a model is no mean feat. To this aim, the paper on hand discusses the complexity of applying genericity, flexibility, and modularity in system modeling and proposes a generic architecture to build modular and flexible simulation models for container terminals. This architecture is split into a set of smaller, manageable, well-connected, and generic modules that facilitate the creation of highly parametrized specific models. An illustrative example of the architecture usage is presented in a case study, the new container terminal of Stockholm, and the resulting models were validated by subject matter experts. Finally, to prove its efficiency, a numerical study fed with real data is conducted to investigate the handling capacity of the studied system under different handling and flow scenarios. The obtained results show that the terminal handling capacity can be increased by around 50% if three to four more straddle carriers are added to the existing fleet.

As a type of intermodal terminal, pure Ro-Ro terminals are one of the most important logistic hubs in the supply chain for rolling freight stored in containerized and wheeled steel boxes. These large-scale systems are highly complex, with nonlinear and hard-to-predict behavior evolving in a stochastic environment. Consequently, making decisions about any problem thereof is no mean feat, particularly for terminal planners. To assist them in decision-making, a pool of relevant models and tools have been developed over the years in the literature. Nevertheless, models that are oriented toward specific objectives dominate, and generic ones are rare. This paper tries to fill this gap and proposes a generic framework to be used as a factory to create specific decision support models based on simulation for pure Ro-Ro terminals. This framework is formulated following two artifacts: (1) the known classification of key performance indicators combined with the typical functional and physical organization of pure Ro-Ro terminals; (2) the three main arteries of harbor systems, namely flows, decisions and operations. Then a scalable way of making decisions based on a flexible form of the cost function weighted according to a set of coefficients is integrated. These designed coefficients allow decision-makers a wide flexibly in choosing how the best solutions are determined. An application of this framework is illustrated through a real case study, where the weights are estimated using an expert-profiling based approach then pushed into the OptQuest optimizer to be calibrated before analyzing the results. These results are aggregated, then expressed as scores on a scale of 0 to 1. This is to help terminal planners to easily identify the worst and best planning scenarios as well as the relationships and compatibilities between the involved handling rules to suggest different alternatives for managing operations.

In this master thesis the performance of external viscous dampers attached to cables in cable-stayed bridges have been studied. A comparison has been performed between a linear and a non-linear cable model. The comparison was carried out for two bridge cables, one from the Dubrovnik Bridge and the other from the Normandie Bridge. The performance of the dampers have been measured in terms of maximum achieved damping ratio and minimum amplitude of vibration.

The analysis was performed using the finite element method. The damping ratio was measured using both the half-power bandwidth method and by calculating the loss factor. The half-power bandwidth method can only be applied to a linear system. Therefore, the loss factor was evaluated for the linear model and compared to the results obtained using the half-power bandwidth method. From the comparison, it was concluded that the damping ratio evaluated using the loss factor was similar to the results obtained when using the half-power bandwidth method. However, when calculating the loss factor, it was of great importance that the resonance frequency of the system was accurately determined. The loss factor was then calculated for the non-linear model and compared to the results obtained for the linear model. Since the loss factor measures the energy dissipated in a system, it could be utilised for the non-linear model. When computing the strain energy for the non-linear model an approximate method was used to take into consideration the strain energy caused by the static deformation of the cable.

From the comparison between the linear and non-linear cable models, it was concluded that the optimal damper coefficients obtained by both models are not significantly different. However, there is an uncertainty in the results due to the fact that an approximate method was used when calculating the strain energy for the nonlinear model. It was also observed that a very accurate evaluation of the system’s resonance frequency was needed to calculate the loss factor. It was also observed that the variation in amplitude of vibration for varying damper coefficient was small for all modes of vibration for the Dubrovnik Bridge Cable as well as for the first mode of vibration for the Normandie Bridge Cable. The difference in the results between the two bridge cables needs to be investigated further in order to get a better understanding of the results.

The vertical dynamic interaction between vehicle and railway track is simulated in the time domain using an extended state space vector approach. The track model includes a transition zone between slab track on a bridge and ballasted track on an embankment. By considering a multi-objective optimisation problem, solved using a genetic algorithm, selected vehicle and track responses are simultaneously minimised by optimising the distributions of rail pad stiffness and sleeper spacing in the transition zone. It is shown that the magnitudes of the maximum dynamic loads in the optimised transition zone can be reduced to be similar as the magnitudes far away from the transition zone.

A short tribute to pioneers in the development of the plastic design of metal thin-walled cross-sections is presented. This large study investigates altogether fourteen steel and four extruded aluminum cross-sections in detail. Six groups of the cross-sections with various shapes consist of four I-shaped doubly symmetric sections with or without lips; three monosymmetric sections with an axis of symmetry z including T- and diamond sections; four monosymmetric channels with or without lips; two point-symmetric Z-sections; and four asymmetric sections. The four extruded aluminum cross-sections are an I 200a section, a diamond section, and closed oblique and irregular sections. For all 18 cross-sections, the plastic section moduli of three kinds were calculated, namely Wpl,y,nB and Wpl,z,nB for bimoment not considered as a constraint; Wpl,y, Wpl,z, and Wpl,w for bimoment considered as a restraint; and maximum values Wpl,y,max, Wpl,z,max, and Wpl,w,max. The values of cross-section plastic resistances Npl, Mpl,y,Rd, Mpl,z,Rd, and Bpl are calculated in numerical examples too. The values of cross-section properties are calculated in different ways to verify the correctness of the results. The following methods of calculation are used: the rules given in Eurocode EN 1993-1-1:2022; MathCad programs; and freeware. Recommendations for educational institutes and designers in practice are given, including simple formulae for all cross-sectional properties for doubly and monosymmetric I-shaped sections, channels, and Z-sections. The formulae are presented in three tables containing formulae in dimensionless form convenient for parametrical studies and formulae for direct design. The background of the Eurocode rules given in EN 1993-1-1:2022 is explained together with recommendations for how to avoid the problems with using them.

It is inevitable that Structures become older and their intended use changes or the structuralcodes regulations change. In some regions the damage from seismic activities is a possibility.It becomes, therefore crucial to assess the structural capacity of such structures. The purposeof this study is to assess the different methods used for testing and estimating thecharacteristic in-situ compressive strength which is the most vital parameter required instructural assessment.

The focus of the study is for existing structures where there is no prior knowledge about theconcrete strength. This study first investigates and evaluates the merits and demerits of thesemethods for investigation of the condition of in-situ compressive strength of concrete inexisting structures. A case study of the Skuru bridge that was built in 1914 was utilized forthis study. The study is based on information of the construction data and some results fromprior investigation performed by the company COWI. Afterwards, non-destructive tests werecarried out with the UPV and Rebound hammer to assess the quality of the concrete.

In addition, the study assesses the use of different interpretation methods with regards toreliability and practical application. The results were interpreted in accordance to theEuropean codes, Swedish codes and other interpretation methods. The difference of theresults from the different interpretation methods are compared and evaluated for reliabilityand efficiency.

The test results confirmed that the concrete consisted of the same strength class. However,the results from the different interpretation methods are dissimilar. The reason for obtainingdifferent results is because the methods depend on different methodologies. The studyshowed that some methods can sometimes overestimate the results and become unsafe forstructural assessment. On the contrary, the other methods can yield lower but safer estimates.

Moreover, the use of small number of cores is evaluated for various methods. The reasons arebecause in practice, the preference is to avoid large number of cores. As a result, it isrecommended to apply care and proper judgment in selection of the methods andinterpretation of the results. It is also recommended to consider the methods with respect tothe aim of the investigation, their limitations and assumptions.

This work has been done in collaboration with Northpower Stålhallar AB. The work is concentrating on column buckling, wind load and deflection of steel columns made of VKR profiles. VKR profiles are steel profiles that are hot-rolled structural pipes having a rectangular section. The analysis is made according to Eurokod 3 and with the finite element program Abaqus. A comparison has been made between these to see whether they differ in result or not regarding buckling curves and interaction formulas. In addition, the company wanted calculation templates in Excel. A proposal for a spreadsheet for different deflection limits are presented in Excel that the company can use, as well as a calculation template for wind loads where all municipalities in Sweden are included. The report contains theoretical background on how to design columns with respect to buckling, wind loading and deflection according to Eurokod 3.The work with Abaqus includes linear and non-linear analysis of column buckling. The analyses also include geometric imperfections, residual stresses, and plastic behavior of steel. The result showed a slight difference between Eurokod and Abaqus analyses but it was not a considerable deviation.

Detta arbete bygger på en jämförelse mellan Boverkets Byggregler och Eurokoder för en befintlig limträkonstruktion. Referensobjektet är en tennishall belägen i Botkyrka kommun. Objektet byggdes under början på 90-talet i form av en treledsram med taktäckning av PVC duk som vilar direkt på limträbalkarna, inklusive en inre duk med mellanliggande isolering och luftspalt. Under de senaste åren har konstruktionen uppvisat tecken på svagheter med bl.a. stora sprickor i limträbalkarna, dessa skador kulminerade i att på begäran av kommunen stänga av anläggningen för fortsatta spel.

Oavsett om beräkningarna utförs med BKR eller Eurokoder som är norm idag så har stommen inte tillräckligt bärighet för sin egentyngd och dagens snölast. Detta kan tyckas vara märkligt men förklaringen kan vara att man utförde byggnaden med tanke på att snön glider av hallen och inte ackumuleras. Med detta i åtanke skulle snön glida av om yttertaken hade hållits varm, mycket tyder på att så skulle ha varit fallet om fläktarna som luftar spalten i takkonstruktionen hade varit igång. Enligt Roger Vintemar, verksamhetschef för Idrott och Anläggning på Botkyrka kommun, har fläktaggregatets på/av knapp placerats lättillgängligt i spelargången och det finns anledning att misstänka att fläktaggregatet har varit avstängd vid långa perioder. Sprickorna i bågarna kan bero på överlast eftersom snön har ackumulerats och inte glidit av. Med avseende på hur konstruktionen är utformad och att det har blivit vattenansamlingar på spelbanan är det inte orimligt att ifrågasätta dragstagets rostskydd. Skulle dragstaget som håller ihop de två bågarna brista finns det en överhängande risk för s.k. sprött brott med ett snabbt ras till följd.

The problem addressed in this thesis is the dynamic behavior of end-frame railway bridgessubjected to high-speed train loading, with a particular focus on soil-structure interaction(SSI). The Swedish Transport Administration (Trafikverket) has high demands for suchbridges due to the dynamic loads imposed by trains traveling at speeds up to 320 km/h.

Addressing this issue involved extensive use of Python to develop a parametric spaceincluding bridge parameters such as span length, beam height, cantilever length, endframeheight, end-frame thickness, bearing pad width, and haunch dimensions. The initialdata set included a number of bridges that were not feasible from a static point of view.In order to filter them out, a 2n-factorial experiment was conducted, resulting in a datasetof different end-frame bridge configurations to evaluate their impact on both static anddynamic responses. Using this dataset, a static analysis was conducted to obtain sectionforces such as bending moments, shear forces, and displacements. The results were thenused to filter out non-buildable bridge designs, validated through Eurocode standards.

The dynamic response of these statically buildable bridges from the dataset wasinvestigated using a High-Speed Load Model (HSLM) module from Tyréns, simulatingthe dynamic effect on the bridge structures. Given the large dataset with discretizedend-frame bridges, significant computational resources were required. Therefore, theHSLM analysis was conducted on a supercomputer at the KTH/Parallel Data Centre(PDC) to obtain efficient computation. This analysis yielded kinematic quantities suchas accelerations, rotations, and displacements, which were checked against Eurocodestandards.

Key factors influencing the structural performance of these bridges were identifiedthrough a correlation study of the bridge parameters against the kinematic responses. Thiscorrelation analysis assumed linear/non-linear relationships between the parameters andthe kinematic variables. Additionally, an analysis of the FRF’s used in the computationswas also conducted to confirm the findings from the correlation study and do understandthe dynamic properties of the model, as well as to validate that the HSLM-analysis wascorrectly implemented in the parametric space.

The study revealed that increasing the end-frame length and thickness significantlyreduces acceleration, with additional benefits observed from incorporating wingwalls.Raising the beam height effectively lowers the dynamic response amplitude, though itmay pose challenges for environmental impact and static stability, when regarding thevertical deflection of the main beam. Increasing the span length reduces accelerationbut increases displacement and rotation, while shortening the console length decreasesthe response amplitude across all components. The influence of haunches on dynamicbehavior remains unclear, requiring further investigation to determine their effectivenesswithin the dynamic parameter space.

Concrete has a significant influence on the global warming due to its high usage in the construction industry. There are a few different strategies to increase the sustainability potential of concrete structures. Most of these strategies involve reduction of the total clinker content. One strategy, which is often neglected due to its complexity, is to increase the durability of the concrete structure. By increasing the durability, the need for repair and maintenance is reduced and thus less resources are consumed during the service life. One of the main deterioration mechanisms in concrete structures is the corrosion of steel reinforcement. A strategy to increase the service life of concrete structures in harsh environment would therefore be to increase the durability of concrete or to use low- or non-corrosive reinforcement instead of traditional steel reinforcement. This paper focuses on the latter. Glass fibre reinforced polymer (GFRP) bars are non-corrosive and have emerged as an alternative to steel bars in reinforced concrete structures in harsh environment. They have other mechanical properties than steel and opens for alternative mix designs for concrete. However, the environmental impact of concrete structures reinforced with GFRP bars has not been fully investigated and most life-cycle assessment (LCA) studies have an exchange ratio of 1:1 between GFRP and steel bars despite differences in the mechanical properties. This paper studies the climate impact of concrete columns reinforced with GFRP bars through an LCA methodology, focusing on the functional unit.

High-speed railway is expanding drastically in Sweden, necessitating new technology, and improve-ments of existing structures. End-shield bridges are a common and under-tested bridge type inSweden. Their dynamic performance is significantly impacted by their boundary conditions due to thesoil–structure interaction (SSI) and their large masses cantilevering beyond the footings. A specificend-shield bridge was tested under low (5 kN) and high (20kN) amplitude-forced hydraulic excitationfor a wide range of frequencies. Several train passages for typical passenger trains,‘X62’, were meas-ured with the same experimental setup. The results were analysed to isolate the significant modes ofthe system and the natural frequencies. A full 3D numerical model was calibrated and updated inAbaqus, along with a brief sensitivity study to determine the most influential parameters. Finally, theresponse to passing trains and Eurocode design HSLM trains was calculated. The experimental studyshowed that higher loading amplitudes resulted in higher damping and lower natural frequencies. Thenumerical analysis showed that for this bridge type the SSI cannot be neglected and can be success-fully introduced in the model.

The paper presents details of a numerical analysis and simplified construction of strengthened glue laminated beams. Glue laminated beams are strengthened through the use of steel reinforcements embedded between the lamellas of the beams. The study compares the numerical results from reinforced and prestressed beams, simply reinforced beams and non-modified beams. Parametric studies were undertaken to evaluate the effects on reinforcement thickness, beam span, prestressing force and prestressing loss. Modified and prestressed beams with wide spans and large dimensions had a significantly higher design load compared to non-modified beams with similar geometry and span. In the most beneficial cases, a load increase of 438% was observed for point load at midspan and 346% for uniformly distributed load.

Slender elements in framed structures may undergo large displacement and experience highly nonlinear behavior. This paper presents a two-node co-rotational flexible beam with generalized elasto-plastic hinges at the beam ends. A Condensation procedure is used to remove the internal degrees of freedom so that the formulation is easily incorporated with the standard co-rotational approach. A family of asymmetric and convex yield surfaces of super-elliptic shape is considered for the plastic behavior of the hinges. By varying the roundness factor, an infinite number of yield surfaces are obtained making it possible to select the yield function that best fit experimental data of any type of cross-section and material. The nonlinear response of bolted connections subjected to both bending and axial forces are conveniently modeled with such a yield surface. Discrete constitutive equations for the hinge plastic deformations are derived using the implicit scheme for both smooth and non-smooth cases. Numerical examples demonstrate the accuracy of the model in predicting the large displacement inelastic response of framed structures. Effect of the roundness factor on the ultimate load strongly depends on the structure typology. It was observed that cyclic loading produces pinching effect, cyclic softening and ductile behavior. Those effects are more pronounced with anisotropic yield criteria.

High-frequency mechanical impact (HFMI) is an efficient post-weld treatment technique  that enhances fatigue strength in metallic welded structures. Steel or steel-concrete  composite road bridges, where the fatigue limit state often governs the design, compose one category of structures that can benefit from the application of this technology. To assert an improvement in fatigue strength using HFMI, the induced compressive residual stresses must be stable. Therefore, the maximum service stresses that can be allowed on HFMI-treated joints should be controlled to avoid the relaxation of the induced beneficial compressive stresses by HFMI treatment. Using statistical analysis of recorded traffic, this paper compares the measured maximum traffic loads to those generated by a load model. More than 870,000 and 470,000 recorded vehicles from traffic measurements in Sweden and the Netherlands are used in this analysis. To capture the characteristic bending moment, the daily maxima of the resulting measured load effect are combined with the extreme value distribution of the bending moment. In addition, it is found that the characteristic load combination is the best-studied option to assess the maximum stress in HFMI-treated weldments in road bridges.

Modern railway infrastructures, especially bridges, are exposed to significant vibrations with potential safety implications. In this context, previous studies have shown the inconsistency and inadequacy of some conventional design methods necessitaing them to be improved. The assessment of safety inherently deals with uncertainties. Therefore, the current study is dedicated to this objective using reliability-based methods. Of the various possible failure modes, the investigations presented here are limited to running safety and passenger comfort. The investigation of these limit-states requires constructing complex computational models with train-track-bridge interaction capabilities. However, the application of these computationally intensive models in the context of structural reliability does not appear to be feasible. Simplifying the system, the vertical acceleration and the deflection of the bridge serve as implicit limit-state measures. Initially, using First Order Reliability Method (FORM) revealed limitations in the application of the current safety factor, resulting in inconsistent reliability indices. Therefore, probabilistic design curves are proposed, defining minimum required bridge mass and stiffness based on cross-section types, span configurations and train speeds. These results are obtained by formulating a FORM-based optimization. Subsequently, the results are used to investigate the sensitivity of the estimated failure probabilities with respect to the contributing basic random variables. Acknowledging the limitations of FORM, surrogate-assisted simulation-based reliability assessments were used for further investigations. A comparison of the performance of widely used regression-based surrogate models under an identical active learning scheme showed the superior performance of the Kriging method over the others. Within areliability-based design optimization framework, this Kriging model facilitates the generation of new probabilistic design curves. This is achieved by reformulating the conventional method to account for the dependency between design variables using the copula concept. In addition, the surrogate model aided in calibrating the safety factor associated with the vertical acceleration threshold, leading to a proposal of 1.38 as a new safety factor. Subsequently, the influence of soil-structure interaction on the estimated reliability indices is evaluated using an ensemble of classification-based surrogate models. Results highlighted its beneficial contribution in terms of increased damping for shorter spans, countered by adverse effects due to frequency shortening in longer bridges. Finally, the epistemic uncertainties arising from the limited knowledge of the vertical acceleration threshold are investigated. It is found that neglecting these uncertainties can lead to an overestimation of allowable train speeds by about 13%.

Increasing the operational speed of trains has attracted a lot of interest in the last decades and has brought new challenges, especially in terms of infrastructure design methodology, as it may induce excessive vibrations. Such demands can damage bridges, which in turn increases maintenance costs, endangers the safety of passing trains and disrupts passenger comfort. Conventional design provisions should therefore be evaluated in the light of modern concerns; nevertheless, several previous studies have highlighted some of their shortcomings. It should be emphasized that most of these studies have neglected the uncertainties involved, which preventsthe reported results from representing a complete picture of the problem. In this respect, the present thesis is dedicated to evaluating the performance of conventional design methods, especially those related to running safety and passenger comfort, using probabilistic approaches. To achieve this objective, a preliminary study was carried out using the first-order reliability method for short/medium span bridges passed by trains at a wide range of operating speeds. Comparison of these results with the corresponding deterministic responses showed that applying a constant safety factor to the running safety threshold does not guarantee that the safety index will be identical for all bridges. It also shows that the conventional design approaches result in failure probabilities that are higher than the target values. This conclusion highlights the need to update the design methodology for running safety. However, it would be essential to determine whether running safety is the predominant design criterion before conducting further analysis. Therefore, a stochastic comparison between this criterion and passenger comfort was performed. Due to the significant computational cost of such investigations, subset simulation and crude Monte-Carlo (MC) simulation using meta-models based on polynomial chaos expansion were employed. Both methods were found to perform well, with running safety almost always dominating the passenger comfort limit state. Subsequently, classification-based meta-models, e.g. support vector machines, k-nearest neighbours and decision trees, were combined using ensemble techniques to investigate the influence of soil-structure interaction on the evaluated reliability of running safety. The obtained results showed a significant influence, highlighting the need for detailed investigations in further studies. Finally, a reliability-based design optimization was conducted to update the conventional design method of running safety by proposing minimum requirements for the mass per length and moment of inertia of bridges. It is worth mentioning that the inner loop of the method was solved by a crude MC simulation using adaptively trained Kriging meta-models.

As far as the authors are aware, the threshold for vertical acceleration of the bridge deck was chosen based on the assumption that the induced dynamic loads would overcome gravity at higher accelerations, resulting in loss of contact between wheels and rail; however, the previous studies do not support this hypothesis. Considering these inconsistencies, a better understanding of the simplified design criteria is essential before conducting further studies suchas the calibration of partial safety factors. Therefore, this study considers a set of representative design scenarios to statistically compare wheel-rail contact loss with other criteria that can bederived from moving load models, such as vertical accelerations and bridge deck deflections. Based on the analyzes performed, deflection seems to be a better criterion than acceleration to control the running safety limit-state; although the results presented do not necessarily show avery strong correlation between these two criteria. Therefore, the k-means clustering approach isused together with 5% lower quantiles of the collected data to propose potential new thresholds. It should be noted that due to the limited number of analyzes, the approach presented in this study can be considered as a possible framework for further updates of the current design method rather than drawing general conclusions.

There is a growing intent among engineers, stakeholders, and decision makers to use probabilistic methods for infrastructure assessment or design objectives. However, the corresponding limit state for such problems usually requires the construction of complex computational models, usually using commercial software without parallelization capability. Such a requirement makes performing reliability analysis computationally prohibitive, which is even more challenging for dynamic problems, since a very short time step is required to obtain sufficiently accurate predictions. This concern has led to several methods being proposed to surrogate the limit state function with a generally black box called a meta-model. A variety of them, such as Kriging, Polynomial Chaos Expansion (PCE), Artificial Neural Networks (ANN), and response surfaces (e.g., polynomial, spline, or radial-base functions), have been adopted for this purpose. These meta-models are typically trained on a limited data set collected by computing the true responses of carefully selected input variables. Their applicability for assessing the probability of failure has been studied individually in the literature for both benchmark and practical problems. However, as far as the authors are aware, no comparison has been made between them for dynamic problems. This comparison needs to be made from the point of view of both accuracy and performance (number of calls to the limit state function). In this context, this paper takes a systematic approach to evaluate their performance under identical conditions, i.e., with similar training datasets. For this purpose, the dynamic response of railway bridges with different spans excited by the passage of trains with a wide range of speeds is used as a reference problem.

Excessive vertical acceleration of ballastless railway bridges subjected to vibrations induced by passing trains is one of the governing design criteria for bridges in high-speed lines. However, to the authors' knowledge, the corresponding design limit is not based on a solid theoretical or experimental background. Moreover, the traditionally applied safety factor also suffers from these concerns. Therefore, in the present study, a crude probabilistic approach is adopted to evaluate the consistency and reliability of this safety factor. For this purpose, deterministically designed bridges (using conventional methods) with short to medium spans are considered. Then, their reliability is evaluated using simulation-based techniques and extreme value theory, i.e., tail approximation. Then, the existing safety factor is calculated to evaluate the consistency of the current approaches, and possible new values are proposed based on the desired target reliabilities.

Operating high-speed trains imposes excessive vibrations to bridges raising concerns about their safety. In this context, it was shown that some conventional design methods such as those related to the running safety suffer from a vague scientific background questioning their reliability or optimality. Therefore, the current article is devoted to updating the conventional design methodology, using Reliability-Based Design Optimization (RBDO) to propose the minimum allowable mass and stiffness which assures satisfying the target reliability. These proposed minimum design values can conceptually replace the conventional partial safety factor-based design method for running safety without the need for dynamic analysis. If the mass and stiffness resulting from the control of other limit states meet the proposed minimum values, the desired target reliability for running safety will be assured. This is achieved by adaptively training Kriging meta-models as a surrogate for the computational models decoupling the RBDO problem. In this regard, a new stopping criteria is proposed using mis-classification ratio of the cross-validated model; which reduces the generalization error of the trained meta-model and consequently the estimated failure probability. Moreover, due to the dependence of the design variables, the Copula concept is used to refine the augmented space and reformulate the RBDO problem.

Traditionally, regulations employ semi-probabilistic methods with partial safety factors to control design limits. Calibrating these partial safety factors involves estimating the target reliability level and optimizing the partial safety factor values in order to minimize the deviation of the safety index between the considered design scenarios and the target value. This procedure necessitates performing a demanding amount of reliability analyses and is often carried out for simplified design situations. Therefore, high computational costs must be accepted for design problems formulated with complex computational models. This study implements a meta-modeling approach based on active learning in the partial safety calibration procedure, enabling its application to computationally intensive problems. Subsequently, the approach is applied to the running safety of ballasted high-speed railway bridges. This limit state implicitly accounts for the phenomenon of ballast destabilization, the occurrence of which disturbs the load path from the rail level to the bridge structure. The dramatic increase in train operating speeds in recent decades has increased the possibility of this design limit state being violated due to resonance. Despite the evident safety concerns, the adopted safety factors appear to be solely based on engineering judgments rather than calibration through higher-level reliability analysis. Therefore, the proposed calibration method is employed to determine the corresponding partial safety factors for various maximum allowable operating train speeds. The newly calibrated partial safety factors allow for a permissible maximum vertical acceleration of the bridge deck approximately 25% higher than the conventional design approaches. Therefore, incorporating these factors into the design procedure may lead to the construction of lighter bridges.

Increasing the operating speed of trains in modern railway networks can induce greater actions on the infrastructure than was previously the case. This is due, in particular, to the occurrence of the resonance phenomenon in railway bridges, which is the focus of this article and was not traditionally considered as a concern. In this context, the vibrations experienced by bridges, both vertical accelerations and displacements, are limited by design regulations to ensure that the safety of train passages over bridges and the comfort of passengers are guaranteed. However, previous studies have shown that the conventional dynamic design methods do not always result in conservative designs, nor is the achieved safety always consistent. Therefore, a probabilistic approach is adopted in this study to optimize the cross-section properties of various railway bridges in a widedesign range including section types, span lengths, and number of spans. For this purpose, an iterative line search based optimization problem is formulated to minimize the depth of the cross-sections under consideration and consequently the linear mass of the bridges. Meanwhile, the associated failure probabilities of the above dynamic limit states are constrained to be less than the desired level of safety by incorporating them in to the optimization constraint. In this regard, First Order Reliability Method (FORM) is adopted to perform reliability analyses. Thus, the obtained results are presented in the form of design curves that may assist designers to select minimum cross-section dimensions satisfying the desired level of safety in terms of dynamic limit states. This objective can be achieved using the proposed design curves without the need to construct associated complex computational models and perform computationally expensive dynamic analyses.

Increasing the operating speed of trains in modern railway networks can induce greater actions on the infrastructure than was previously the case. This is due, in particular, to the occurrence of the resonance phenomenon in railway bridges, which is the focus of this paper and was not traditionally considered as a concern. In this context, the vibrations experienced by bridges, both vertical accelerations and displacements, are limited by design regulations to ensure that the safety of train passages over bridges and the comfort of passengers are guaranteed. However, previous studies have shown that the conventional dynamic design methods do not always result in conservative designs, nor is the achieved safety always consistent. Therefore, a probabilistic approach is adopted in this study to optimize the cross-section properties of various railway bridges in a wide design range including section types, span lengths, and number of spans. For this purpose, an iterative line search-based optimization problem is formulated to minimize the thickness of the cross-sections under consideration and consequently the linear mass of the bridges. Meanwhile, the associated failure probabilities of the above dynamic limit states are constrained to be less than the desired level of safety by incorporating them into the optimization constraint. In this regard, First-Order Reliability Method (FORM) is adopted to perform reliability analyses. Thus, the obtained results are presented in the form of design curves that may assist designers to select minimum cross-section dimensions satisfying the desired level of safety in terms of dynamic limit states. This objective can be achieved using the proposed design curves without the need to construct associated complex computational models and perform computationally expensive dynamic analyses.

The increasing speeds of modern trains lead to excessive vibrations on the bridges, which have the potential to destabilize the ballast particles of the track. The occurrence of this phenomenon not only increases the track maintenance cost, but can also disrupt the load path from the rail level to the bridge deck, posing a risk to the train running safety. The design regulations indirectly control this limit-state by limiting the vertical acceleration of the bridge deck to a threshold value. The assessments pertaining to this purpose often neglect the soil-structure interaction (SSI) effects considering that as a conservative assumption. Such effects can positively contribute by increasing the system damping, but they can also increase the bridge flexibility making it more susceptible to vibrations. Therefore, this study investigates the influence of considering/disregarding SSI effects on the running safety criterion using a probabilistic methodology. The results are classified based on the maximum permissible train speeds and the bridge span length. Due to the high computational costs of the reliability analyses, the limit-state is approximated by an ensemble of classification-based surrogate models using the stack-generalization concept. Subsequently, the upper/lower bounds of the failure probability in the presenceof SSI effects are compared with those obtained for simply-supported bridges. It is pointed out that neglecting SSI effects for shorter span bridges may lead to an underestimation of system safety. For longer span bridges, however, this may lead to an overestimation of safety, which means that a non-conservative system can be designed.

The operational speed of the trains is intended to be significantly increased forthcoming; which consequently questions the safety level of the current design concepts concerning different performance limits. Thus, the reliability of the simply supported single-span bridges is assessed in the current article adopting the first-order reliability method (FORM) approach. In this regard, the dynamic response of the aimed bridges is investigated under the passage of a series of moving loads using available closed-form solutions in the literature. Hereof, axle load, car body/train configuration, flexural rigidity, damping, mass and model uncertainties are considered as random variables; while train-track-bridge interactions are neglected and the procedure is repeated for a wide range of span lengths and train velocities. Then, the safety index corresponding to each case is evaluated by considering running safety as the limit state function; where, the bridge deck vertical acceleration is taken as the capacity of the system. The outcomes are presented as average probability of exceeding the limit state versus train speed and categorized based on span lengths.

The operational speed of the trains is intended to be significantly increasedforthcoming; which consequently questions the safety level of the current design conceptsconcerning different performance limits. Thus, the reliability of the simply supportedsingle-span bridges is assessed in the current article adopting the first-order reliabilitymethod (FORM) approach. In this regard, the dynamic response of the aimed bridges isinvestigated under the passage of a series of moving loads using available closed-form solutions in the literature. Hereof, axle load, car body/train configuration, flexural rigidity,damping, mass and model uncertainties are considered as random variables; while traintrack-bridge interactions are neglected and the procedure is repeated for a wide range ofspan lengths and train velocities. Then, the safety index corresponding to each case isevaluated by considering running safety as the limit state function; where, the bridge deckvertical acceleration is taken as the capacity of the system. The outcomes are presentedas average probability of exceeding the limit state versus train speed and categorized basedon span lengths.

The operational safety of high-speed trains traversing ballasted bridges is contingent upon the prevention of the ballast destabilization, which can interrupt load transfer from the rail to the bridge. Current design regulations indirectly address this limit-state by specifying a threshold value for the vertical acceleration of the superstructure. This value represents the condition at which the inertial forces induced by train passage exceed the resistive forces. However, this approach is based on limited experimental data and the influence of numerous parameters remains unexplored. As a result, reliability analyses pertaining to running safety are hampered by a lack of knowledge, leading to greater epistemic uncertainties. In this study, the impact of such uncertainties on this dynamic system is investigated using surrogate-based Imprecise Structural Reliability Analysis (ISRA). For this purpose, parametric probability boxes are used to represent lower and upper bounds of the cumulative distribution function for basic random variables with epistemic uncertainties and surrogate models are adaptively trained to reduce computational costs. The obtained results show that neglecting the influence of epistemic uncertainties can lead to permissible operating train speed higher than the speed corresponding to the desired reliability level. In this study, an overestimation of about 13% was observed on average. Furthermore, the rough analyses carried out show that taking epistemic uncertainties into account can lead to a reduction of the system characteristic safety factor by up to 30%. This significant reduction underlines the importance of expanding the available knowledge on the phenomenon of ballast instability.

After the industrial revolution, the modern human revised his point of view regarding development and generally his expectations from life. The new idea led him to defeat nature instead of traditional life philosophy stressing harmony and compatibility. It may seem exaggerated but the modern human ignored Mother Nature by violating history lasting peace and starting a battle. Thus, he invented modern instruments (machines) empowered by new energy sources. The greatest portion of this energy demand was supplied by fossil fuel consumption; which in spite of its undeniable role in intended development, numerous drawbacks are distinguished. For instance, it is estimated that the average temperature of the earth is approximately 0.8°C increased since the 1970s. The current chapter does not concern rejecting achieved progress; nevertheless, it aims to highlight the potential of learning from traditional architecture and adopting their experiences to fulfill modern expectations. In this regard, Iranian classical architecture, particularly at hot arid climate, is taken into account. Thus, relevant literature is surveyed to extract developed strategies leading to energy saving in residential buildings. Wider use of renewable energy and elevated energy efficiency are key factors to limiting GHG emissions. Geothermal energy is one of the most significant alternate sources of thermal and electrical energy. The geothermal energy adopted mostly through GCHP systems that are often introduced as ground-source heat pumps (GSHPs). Geothermal heating and cooling systems are heat pumps that extract and convey heat from the ground through a series of liquid-filled, underground pipes connected to a building. It is observed that geothermal heating is more efficient than electric, gas and oil-fried heating. They also are more efficient than air heat pumps as the extract heat from and inject heat into the ground since the ground temperature is almost consistent in different seasons comparing to the air temperature.

Increasing operating speeds and axle loads of trains may induce higher verticaldeck accelerations on bridges, which may subsequently lead to the occurrence of ballast instabilities.This phenomenon not only increases maintenance costs but also leads to speed restrictionsunder operating conditions. In severe cases, it can also cause train derailment. Thishas been shown to be the governing criterion for the design of short to medium span lengthhigh-speed railway bridges, especially from the dynamic behaviour point of view. Despiteits substantial importance in the design of railway bridges, the conventional deterministic approachescannot achieve the desired level of safety (Allahvirdizadeh et al. 2020). Therefore,this article is devoted to the evaluation of the probability of violating running safety usingsimulation-based methods. In this context, different variables, including those for the bridge(span length, flexural rigidity, and geometric properties), for the train (axle load, dominantfrequency and damping ratio) and for the boundary conditions (soil and foundation properties)are considered. Due to the high computational cost and complexity of the consideredperformance function, a low-cost meta-model is trained using stack modelling concept as acombination of support vector machines (SVM), k-nearest neighbours (k-NN) and decisiontrees. Then, the range of maximum and minimum probabilities of exceeding the verticalacceleration threshold are evaluated as a function of train speed and bridge span length. Comparingthese boundaries with corresponding results of simply-supported bridges showed thatneglecting soil-structure interaction effects in shorter span bridges may result an underestimatedsafety of the system; however, for longer span bridges it may result in overestimatedsafeties.

Constructing high-speed railway networks received a great attention during pastdecade raising new safety concerns on infrastructure (particularly bridges). It ismainly because of possible excessive vibrations due to higher operating speeds.In this regard, deficiency or vague scientific background for some of designmethodologies are shown by former studies; among which is the adopted safetyfactor for running safety. This limit state occurs if the load path from the trainto the bridge is disturbed by dislocating ballast particles because of excessivevertical accelerations of the bridge deck. Hence, the current article is devotedto update the conventional design methodology. For this objective, reliabilitybaseddesign optimization technique is employed to propose minimum allowablemass and stiffness (or maximum permissible fundamental frequency) which assuressatisfying target reliability level. This is achieved by adaptively trainingKriging meta-models to surrogate the computational models. It seems that theproposed method can result in lighter (economical) bridges in comparison tothe conventional design methodology; however, this beneficial aspect vanishesby increasing span length of the bridge.

Limiting the maximum vertical acceleration and deflection of the deck are two principal design criteriaof high-speed railway bridges. The former prevents ballast instability to ensure running safety, andthe latter attempts to limit the acceleration of the car-body below the level at which passengercomfort is disturbed. The previous studies are mainly concerned with the destabilization of the ballast,nevertheless the possibility of the maximum deflection occurrence should not be underestimated.Moreover, the literature indicates the need to improve the current design requirements including theminimum allowable mass and frequency of bridges, which requires solving optimization problems basedon modern requirements. Therefore, a probabilistic framework with simulation-based techniques is usedto evaluate the violation probability of the above limit states and distinguish dominant criteria underdifferent conditions, i.e., bridge span length and operational train speed. First, the performance of thesubset simulation method is compared with the Latin Hypercube-sampling based Monte-Carlo approachsupported by surrogate models. Polynomial chaos expansion (PCE) surrogate models are trained for thisobjective. Then, the resulting violation probabilities are evaluated for the two considered limit statesusing the approach with better performance.

The paper deals with the derivation of a local elasto-plastic finite element formulation of three dimensional corotational beams with arbitrary cross- section. Based on Bernoulli beam kinematics, an improved displacement field is constructed by inclusion of second-order terms of cross-section local rotations. The formulation captures both the Saint-Venant and warping torsional effects of open cross sections. Numerical tests show that the inclusion of the second-order terms of the local bending curvatures gives more accurate and more efficient element that allows a significant reduction of the computational time.

The corotational technique is adopted here for the analysis of three-dimensional beams. The technique exploits the technology that applies to a two-noded element, a coordinate system which continuously translates and rotates with the element. In this way, the rigid body motion is separated out from the deformational motion. In this paper, a mixed formulation are adopted for the derivation of the local element tangent stiffness matrix and nodal forces. The mixed finite element formulation is based on an incremental form of the two-field Hellinger-Reissner variational principle to permit elasto-plastic material behavior. The local beam kinematics is based on a low-order nonlinear strain expression using Bernoulli assumption. The present formulation captures both the Saint-Venant and warping torsional effects of thin-walled open cross-sections. Shape functions that satisfy the nonlinear local equilibrium equations are selected for the interpolation of the stress resultants. In particular, for the torsional forces and the twist rotation degree of freedom, a family of hyperbolic interpolation functions is adopted in lieu of conventional polynomials. Governing equations are expressed in a weak form, and the constitutive equations are enforced at each integration cross-section along the element length. A consistent state determination algorithm is proposed. This local element, together with the corotational framework, can be used to analyze the nonlinear buckling and postbuckling of thin-walled beams with generic cross-section. The present corotational mixed element solution is compared against the results obtained from a corotational displacement-based model having the same beam kinematics and corotational framework. The superiority of the mixed formulation is clearly demonstrated.

This paper presents a corotational formulation of a three-dimensional elasto-plastic mixed beam element that can undergo large displacements and rotations. The corotational approach applies to a two-noded element a coordinate system which continuously translates and rotates with the element. In this way, the rigid body motion is separated out from the deformational motion. In this paper, a mixed formulation is adopted for the derivation of the local element tangent stiffness matrix and nodal forces based on a two-field Hellinger-Reissner variational principle. The local beam kinematics is based on a low-order nonlinear strain expression using Timoshenko assumption. The warping effects are characterized by adopting Benscoter theory that describes the warping degree of freedom by an independent function. Shape functions that satisfy the nonlinear local equilibrium equations are selected for the interpolation of the stress resultants. This local element, together with the corotational framework, can be used to analyze the nonlinear buckling and postbuckling of thin-walled beams with generic cross-section. The mixed formulation solution is compared against the results obtained from a corotational displacement-based formulation having the same beam kinematics. The superiority of the mixed formulation is clearly demonstrated.

A local elasto-plastic formulation, based on a low-order nonlinear strain expression using Bernoulli beam kinematics, is presented in this paper. This element, together with the corotational framework proposed in (Comput. Meth. Appl. Mech. Eng. 2002; 191(17): 1755-1789) can be used to analyze the nonlinear buckling and postbuckling of thin-walled beams with arbitrary cross-section. The formulation captures both the Saint-Venant and warping torsional effects of open cross-sections. Numerical examples show that this local formulation is more efficient than the one proposed in (Comput. Meth. Appl. Mech. Eng. 2002; 191(51):5811-5831) based on a Timoshenko beam assumption.

The corotational technique is adopted for the analysis of 3D beams. The technique applies to atwo-noded element a coordinate system which continuously translates and rotates with the element. Inthis way, the rigid body motion is separated out from the deformational motion. Then, a mixedformulation is adopted for the derivation of the local element tangent stiffness matrix and nodal forces.The mixed finite element formulation is based on an incremental form of the two-field Hellinger-Reissnervariational principle to permit elasto-plastic material behavior. The proposed element can be used toanalyze the nonlinear buckling and postbuckling of 3D beams. The mixed formulation solution iscompared against the results obtained from a corotational displacement-based formulation having thesame beam kinematics. The superiority of the mixed formulation is clearly demonstrated.

The purpose of this paper is to present eight local elasto-plastic beam element formulations incorporated into the corotational framework for two-noded three-dimensional beams. These formulations capture the warping torsional effects of open cross-sections and are suitable for the analysis of the nonlinear buckling and post-buckling of thin-walled frames with generic cross-sections. The paper highlights the similarities and discrepancies between the different local element formulations. The primary goal of this study is to compare all the local element formulations in terms of accuracy, efficiency and CPU-running time.

Many steel and composite railway bridges were designed using static analysis and a dynamic amplification factor. These bridges are subjected at present time and in future, to more axel loads and higher train speeds which may reduce substantially fatigue service life at specific parts.

The purpose of this study is to investigate two types of dynamic parameters to evaluate fatigue service life of the Banafjäl Bridge. It is structurally a composite railway bridge that is located in north of Sweden.

One of the dynamic parameters is the speed of different types of high-speed train models which will influence the resonance speed and its impact on fatigue. In addition, the overall damping ratio of the structure is varied which has shown to have a significant effect on the fatigue life.

Two dimensional finite element model was created to perform dynamic time history analyses which was utilizing load-time amplitude function. Two types of trains were used to simulate the bridge response dynamically. The model was verified with another study and the results were employed to evaluate the bridge in three critical welded connections with respect to fatigue.

The results show that the speed of the trains has great impact on the fatigue life especially at resonance speed, and that an increase in the damping ratio will prolong the bridge service life. A comparison of fatigue life between dynamic and static analysis of a specific train type is also presented which shows large differences in results.

In response to the planned increase in operational speeds and axle loads of passengertrains that may lead to resonance-induced excessive vibrations in railway bridges,recent studies examined the reliability of bridges concerning train running safety andpassenger comfort limit states. In this respect, valuable information regarding theimportance of input variables can be obtained by conducting Sensitivity Analysis (SA).For instance, the determination of unimportant variables (where they can be treated asconstant) reduces the computational time, which is usually very high for probabilisticsimulations. In some of the previous studies, only deterministic SA has beenperformed. This thesis follows a stochastic approach using Global Sensitivity Analysis(GSA) methods. The considered performance functions are vertical acceleration anddeflection of single track ballasted simply supported reinforced concrete bridges.To reduce the computational time, available semi-analytical solution of a planarbeam under the passage of a series of moving loads is employed. To simulatethe bridge behaviour realistically, simplified methods to account for rail irregularityamplification, train-bridge interactions, and axle load redistribution were adopted.The considered random variables are train modal properties, number of train coaches,bogie spacing, axle spacing and loads, bridge mass, flexural stiffness and damping,and rail amplification factor. The analyses were carried out for a selected set of bridgelengths [10-30]m and a range of train speeds [100-400] km/hr. The study findingsshow that, in both acceleration and displacement, the dynamic response of the bridgeis sensitive to randomness in bridge mass, moment of inertia, coach length, and axleloads. Furthermore, the rail amplification factor and Young’s modulus are primarilyimportant for acceleration and displacement, respectively.

With the development of metropolitan areas, the negative influence of ground-borne vibrationsfrom complex transportation systems and human activities on quality of life of occupants andvibration sensitive equipment become more prominent. Current practices include basing theanalysis on either empirical or numerical approaches. While the empirical approach has beenshown to be unreliable, numerical methods are considered overly complex and unsuitable forpractical applications. Therefore, the task was to conduct a sensitivity analysis to determinewhich parameters could be neglected from the latter without affecting the structural responsebeyond accepted tolerance ranges.A simple three-story, single-span steel structure with two rigid foundations was analyzedfor this purpose. The structure is founded on a homogeneous stratum (shear wave velocityof Vs = 225 m/s) with bedrock located at a depth of 11 meters, and it is subjected to a unitharmonic load 10 meters away from the structure. Due to the capability to internally account forSSI effects, the numerical Direct Method was used to retrieve a reference solution. On the otherhand, the Substructure Method was used to replicate the reference solution and subsequentlyconduct a sensitivity analysis to identify negligible parameters.It was determined that, for the analyzed structure, solving the equation of motion using onlythe vertical terms of the impedance matrix and the displacement field vector, while enforcingfixed horizontal and rotational boundary conditions, provides a sufficient approximation tothe reference solution in vertical (dominating) direction. Additionally, the analysis alsorevealed that through-the-soil coupling terms of the impedance matrix directly affect the modalproperties of the structure and are vital for the analysis.Additional sensitivity study was conducted regarding the soil stiffness. It showed that withsofter soil, the number of necessary parameters required for sufficient analysis increases.Finally, the analyzed structure was modified by adding a slab at the foundation level. Sucha configuration is a common practice in structural design. The analysis showed that such acomponent significantly improves the approximation using the suggested impedance matrixand displacement field vector, regardless of the soil stiffness.

The advancement of society has led to an increase in demand for infrastructure, particularly bridges, which are designed in accordance with different design codes. In Sweden, bridge design adheres to the Eurocode and national code (TRV specifications), with the most adverse scenario of the two codes determining the basis for bridge design. The process of designing a bridge according to both codes and subsequently comparing them necessitates a prolonged design duration, resulting in an increase in project costs. This thesis explores the possibility of determining multiplication factors αM and αV for the bending moment and shear force respectively, which would enable the direct transition from the most unfavourable load case in the Eurocode to the worst one in the TRV specifications. Thus, the bridge can be modelled based on the most conservative of the two. The study concentrates on portal frame bridges ranging in length from 6 to 25 m, with a 1 m step between each case study and expanding from 1 to 4 traffic lanes. The FEM software "Brigade/Plus" was used to analyse the portal frame bridges, with the key internal forces being the longitudinal bending moments and shear forces in the deck slab. The analysis of the different models showed that bridges with four lanes had αM increasing according to a quadratic relation while αV increased linearly. In the case of three-lane bridges, only one value of αM was greater than one. In conclusion, the analysis indicated that the Eurocode is more conservative for short-span bridges of up to three lanes and less conservative for four lanes above a span length of 16 m.

Long Life Bridges is a Marie Curie 7^th Framework Project funded under the Industry and Academia Partnerships and Pathways call, Grant Agreement No. 286276. The Project commenced in September 2011 and is continuing for 4 years until August 2015. The project vision is to extend the service lives of bridges through development of advanced assessment methods. The author wishes to acknowledge the financial contribution by the European Commission in supporting the project and funding this research.

The work presented in this report has been conducted at Roughan & O’Donovan Innovative Solutions, Dublin, Ireland, during the period of January to December 2012, under supervision of Associate Professor Alan O’Connor. The author has been seconded from the Royal Institute of Technology (KTH), Division of Structural Engineering and Bridges.

Within the project, experimental work to develop a prototype damper has been carried out at Trinity College Dublin (TCD), Department of Civil, Structural and Environmental Engineering. A special thank goes to Dr. Kevin Ryan and the laboratory staff at the Department for the help in manufacturing and testing the prototype damper.

Full-scale testing has been performed on a railway bridge in Sweden. The tests were funded directly by the Swedish Transport Administration (Trafikverket). The instrumentation and field measurements were performed by KTH in collaboration with the author.

The work presented, denoted secondment 1.1b, deals with development of adaptive and semi-active damping systems for railway bridges. The aim of the project is to develop methods for structural vibration control with applications for railway bridge dynamics. Much of the work has been related to a case study bridge.

There is constant demand on rail authorities to increase both the allowable axle loads and the allowable speed on existing railway lines. As an example, the Swedish Transport Administration has recently investigated the possibility of upgrading part of the main lines to allow for future high-speed trains. Some lines are also being investigated with the aim of allowing ore transports with higher axle loads and longer trains. A large portion of the bridge stock was designed for significantly lower axle loads and only very few have been designed to account for dynamic effects. Increased dynamic effects may result in exceedance of dynamic design criteria, reduced service life due to fatigue, or even failure. Through better quantification of risk, it is often possible to prove that speeds can be increased with no adverse effect. However, for bridges where the level of risk is too high, a cost-effective means of reducing dynamic effects on bridges are active and semi-active control system. Semi-active control is well established in other fields and could prove to be a beneficial technique to allow train speeds to be increased.

The concept of structural vibration control is to attenuate the dynamic response of a structure by means of an external damping device. Due to changes in either loading or structural behaviour, the properties of the damper device may need to be changed to efficiently mitigate vibrations. Two main principles of damper devices are commonly used; tuned mass dampers and shock absorbers. Tuned mass dampers consist of a suspended mass mounted on the main structure. Due to a phase-shift, the vibration of the suspended mass partly counteracts the corresponding motion of the main structure. Changing the stiffness of the suspended mass results in a variable adaptive tuned mass damper. Shock absorbers rely on producing the counteracting force by means of increased viscous damping. Devices with variable viscous damping are often categorised as semi-active. Fully active systems rely on producing the counteracting force by means of a load actuator. Adaptive and semi-active systems generally require much less energy to operate compared to fully active systems.