Rolling resistance (RR) is one of the key factors that researchers are trying to minimize due to its significant contribution to greenhouse gas emission and global climate change. This study investigates the impact of asphalt pavement surface distress on RR and its subsequent environmental cost. Motivated by the objective to quantify the environmental implications of deteriorating pavement surfaces, the research aims to facilitate improved prediction of RR using a data-driven Machine Learning (ML) approach, and quantify the environmental cost of surface distress attributable to RR. The study employs a multi-phase methodology, which begins with accurate estimation of pavement texture parameters, followed by an analysis of the effect of surface distress on texture properties. A Random Forest (RF) regression model is used for predicting rolling resistance coefficient (RRC) and the predictions by the model are compared with the predictions by an empirical linear regression model to demonstrate the improvement in prediction performance. RRC values predicted for pavements of different distress levels reveal a clear upward trend of RRC with increasing distress severity, which suggests a strong relation between surface distress and RR. Tire penetration level is calculated for surfaces with different distresses under varying loads. The results reveal non-linear growth in rubber deformation under load, with greater penetration for distressed surface, which suggests direct impact of surface distress on energy loss. Using the predicted RRC values, energy loss, fuel consumption and CO2 emissions associated with RR are calculated for each distress level. Standard carbon pricing is applied to estimate the associated environmental cost. The additional fuel cost borne by road users is also quantified. Results show that increased surface distress results in higher fuel consumption, CO2 emission and corresponding environmental cost attributable to RR. The findings demonstrate the dual economic and environmental burden of pavement distress and underscore the importance of timely pavement maintenance. The study contributes a comprehensive methodology for assessing pavement distress-induced environmental cost and supports data-driven decision-making in pavement asset management. ... Read more

Driven by technological advancements, modern railway systems are increasingly characterized by higher transport capacity and improved sustainability in response to resource constraints and climate change. At present, wheel–rail contact, as the dominant technical approach for railway transportation, serves to guide the train and provide the necessary traction and braking forces. However, this contact is susceptible to defects such as wheel flats, which can cause impact vibrations and noise, and pose safety risks. To effectively detect wheel flats, axle box acceleration (ABA) measurements hold great potential, as it has been widely adopted to monitor track structures and interface deterioration. This study is conducted to develop a reliable 3D finite element (FE) model to simulate wheel flat-induced impacts, and to investigate the effects of the rolling speed and flat parameters on the impact force and ABA responses.

To achieve the research objectives, a 3D FE model with a flat was developed based on the lab test data from V-Track. The finite element analysis was conducted through an implicit–explicit sequential method, and the developed FE model was validated against experimental measurements. With the validated model, a parametric study was conducted to study the effects of wheel rolling speed, flat length, and flat development stage on the impact force and ABA responses, with the latter two parameters investigated by adjusting the discretized tread profiles in the flat region. For all simulated and measured signals, time–frequency features were obtained using Continuous Wavelet Transform and Synchrosqueezed Wavelet Transform. The resulting wavelet power spectra can effectively capture localized energy variations induced by the wheel flat.

The results demonstrate that flat-induced wheel–rail impact force increases non-linearly with wheel rolling speed, and the correlation between the flat length and the impact force is not consistently positive. Moreover, the wear development of the flat leads to a noticeable reduction in impact force at low speeds. The ABA responses are influenced by a combination of factors, including speed, wavelength, and flat-related wheel and track modes. The conclusions and recommendations presented at the end of the thesis highlight the need for a more comprehensive study that considers a broader range of flat geometric parameters to support the development of flat monitoring and the formulation of ABA-based wheel assessment rules. ... Read more

The generation of frictional heat at the wheel-rail interface is a critical factor during train operations, especially during acceleration and braking. High slip ratios can lead to substantial thermal loading due to the rapid accumulation of thermal energy, resulting in significant temperature increases in the contact area. This thermal loading is known to accelerate wear, induce plastic deformation, and cause thermal fatigue in wheel and rail materials. Additionally, high contact temperatures around 720 °C may induce microstructural transformations in the material, leading to the formation of the white etching layer (WEL), which includes brittle martensite and makes the material more prone to cracking. These wheel-rail interface deteriorations increase maintenance costs and impact the operational safety of trains. Therefore, it is vital to investigate the wheel-rail friction-induced temperature and its effects on wheel/rail damage. The aim of this research is to better understand the thermomechanical behavior of the wheel-rail system. Three objectives are accomplished to reach this goal: 1) establish numerical models and experimental setups to accurately assess the thermomechanical behavior of the wheel-rail contact system; 2) reliably validate the thermomechanical contact model by accurately measuring the wheel-rail contact temperature, especially under the high slip ratio conditions; 3) improve the understanding of the generation and development of thermomechanical damage, e.g., polygonal wear and a “wheel flat”… ... Read more

In the Netherlands, there is a large and widely used railway system that includes numerous railway bridges. This master thesis investigates the problems caused by these railway bridges. Since World War II, continu- ous welded rails have been used extensively throughout the Netherlands. These rails offer several advantages on embankments, such as reduced maintenance due to less vibration, increased passenger comfort, and reduced noise. However, continuous welded rails can cause problems when they run continuously over a bridge, as is the case in the Dutch railway system. Bridges are not continuous structures and have joints between the decks or between the deck and the transition structure. These joints allow the bridge deck to expand and contract due to temperature changes, move due to longitudinal forces from train braking and acceleration, and deflect due to the vertical load of the train, causing rotations at the ends of the bridge decks. This relative displacement between the bridge deck and the continuously welded rails creates addi- tional stresses in the rails. These additional stresses must not exceed the maximum allowable stress of the rail material, as this could cause the rails to buckle or fracture. Fixed points are often used in practice to limit the movement of the bridge deck and keep additional rail stresses within acceptable limits. This investiga- tion, however, focuses on understanding the interaction between the rails and the structure without the use of fixed points. The study assumes a railway bridge in the Netherlands with a ballast bed and uses concrete precast bridge decks.

To gain initial knowledge of the problem and the various railway components and bridges, a literature review was conducted, and two existing railway bridge projects were analysed. It quickly became evident that there are two different bridge types relevant to the study of additional rail stresses: those without embankment influence and those with embankment influence. The study then identified parameters that could influence the magnitude of additional rail stresses to use them as variables in further investigations.

Two longitudinal force models were created in SCIA Engineer: one without embankment influence (Model 1) and one with embankment influence (Model 2). These models are spring models where the stiffness of connections and elements is schematised as springs. The models were validated with hand calculations and used to obtain results for the influence of various parameters such as bridge deck span length, elastomeric bearings, bridge pier length, and foundation stiffness. The results of the two models were compared to understand the influence of the embankment. Additionally, the spring elongations of the non-linear springs between the bridge deck and the rails, representing the ballast bed, were examined to determine if they were in the linear or non-linear part of the spring characteristic to see if the springs slipped enforcing stress redis- tribution. Finally, the models assessed the individual contributions of three load cases (thermal, longitudinal traffic load, and vertical traffic load) to the combined additional rail stress.

The results lead to the following conclusions:
• When a structure is not influenced by the embankment, the magnitude of additional rail stresses depends on the stiffness of the substructure. The stiffness of the weakest component, in this case, the elastomeric bearings, has a significant influence.
• When a structure is influenced by the embankment, the magnitude of additional rail stresses mainly depends on the dominant stiffness of the embankment, with the stiffness of the substructure having little to no influence.
• Structures with embankment influence experience lower additional rail stresses due to the additional stiffness provided by the embankment. Problems with exceeding maximum permissible rail stresses occur mainly in relatively long railway bridge structures without embankment influence.
• The vertical load has the largest contribution to the combined additional rail stresses for both structure types.
• The thermal load has a larger influence on structures with embankment influence because these structures are more constrained by the embankment and thus more vulnerable to thermal deformations.
• Linear summation of individual stress contributions from different load cases generally results in higher or equal stresses compared to non-linear combinations, making linear summation a conservative approach. The stress difference between linear summation and non-linear combination is usually only a few megapascals. If the springs between the bridge deck and the rails slip into the non-linear branch, this difference increases slightly but remains small.


Based on these conclusions, the following recommendations can be made to prevent additional rail stresses from exceeding maximum permissible stresses without the use of fixed points and to streamline the process of longitudinal force analysis for engineers:
• To prevent exceeding the maximum permissible stress in structures without embankment influence, consider using larger elastomeric bearings or less slender bridge decks that are less susceptible to deflection, thereby reducing additional rail stress, especially from vertical loads.
• Since linear summation of individual contributions to additional rail stresses results in conservative and faster calculations, it is recommended to use linear calculations in the initial phase. Then, perform a final design review with non-linear calculations to ensure accuracy. This approach will significantly speed up the design process, as models will not need to run for hours or days each time.
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Sustainability has become a paramount concern in modern research, aligning with global efforts to reduce carbon emissions and embrace circular economy principles. The mentioned imperative extends to the field of pavement engineering, where the widening of existing pavements, a common practice to accommodate increasing traffic demands, necessitates sustainable solutions. The current thesis addresses the pressing need for pavement engineering practices that align with ambitious sustainability goals while ensuring structural integrity and performance.

Drawing upon the context of countries like the Netherlands, striving for zero carbon emissions and full circularity by 2030, the research explores avenues for sustainable pavement widening. This involves optimizing designs to minimize material usage, reduce emissions, incorporate recyclable materials, and extend the lifespan of road infrastructure. The challenges posed by non-uniform settlements and stress concentrations at widening joints are investigated, highlighting the importance of accurate material modelling and interface characterization.

Motivated by the need for sustainable pavement solutions, the research aims to guide decision-making in pavement design towards environmental sustainability while meeting functional requirements. The scope encompasses FEM models, EVP behaviour of asphalt surfaces, base layer variations, interface modelling, and comparative analyses between 2D and 3D models.

The current study undertakes a thorough examination of the implications of pavement widening on stress concentrations, material behaviour, and interface modelling, aiming for development of more sustainable and resilient pavement designs. Employing a comprehensive research framework encompassing theoretical modelling and numerical simulations, the study seeks to elucidate the issues inherent in widened pavement structures.

The main thesis objective is the development of an elasto-visco-plastic (EVP) material model, to capture the time-dependent behaviour exhibited by asphalt surfaces under varying loading conditions. Using the Finite Element Method (FEM), the developed material model serves as a foundational pillar for subsequent investigations, facilitating an examination of stress distribution patterns within widened pavement structures.

The Research provides a detailed framework for conducting the study on pavement widenings. It begins with the delineation of study parameters, including cross-sectional geometry, material properties, and simulation techniques. The development and validation of the EVP material model are elaborated, along with the implementation of finite element method (FEM) simulations to analyse stress distributions. Parametric analyses are conducted to investigate the effects of load variations, base layer characteristics, and interface modelling on widened pavement performance. The methodology also includes the utilization of cohesive zone modelling for interface characterization, enabling a more detailed representation of pavement layer interfaces.

The identification of critical stress concentrations emerges as a focal point of inquiry, necessitating a crucial to understand the interplay between load variations, base layer thickness, and material stiffness. Through various numerical analyses, the study seeks to unravel the intricate web of factors influencing stress propagation within widened pavement structures. Moreover, the implications of reduced recessing length and base layers in new pavement designs are subjected to meticulous scrutiny, shedding light on potential trade-offs between structural integrity and resource optimization.


Overall, the current thesis contributes to advancing pavement engineering practices, promoting sustainable transportation infrastructure, and supporting global sustainability goals. Through rigorous analysis and modelling, the research seeks to enhance the understanding of critical factors influencing widened pavement performance, paving the way for safer, more efficient, and environmentally conscious road networks.
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For railway travel the Insulated Rail Joint (IRJ) is a critical part in most railway safety systems but at the same time also considered a weak link. The IRJ creates a discontinuity in stiffness and geometry that leads to wheel-rail impact forces. The angled IRJ is a proposal to reduce these impact forces. Despite the real-world experiences with angled IRJs the research on the topic is marginal. In this thesis a study is presented into the dynamic behaviour of the wheel-rail impact occurring at IRJs. Numerical models are established to simulate a wheel rolling over IRJs with angles of 0, 15, 30 and 45 degrees, using the implicit-explicit sequential finite element method with the software ANSYS/LS-DYNA. The impact forces are the main output and analysed. Three variations of the IRJ models were used for simulations. The basic version IRJ model is built up with a fully constrained rail foot to simulate an infinite support stiffness condition. The second version is supported by spring and damper elements to simulate supports such as ballast and rail pads. Height differences between the rail ends are generated when a wheel passes the joint, which corresponds to a real-world scenario. Different degrees of support degradation are simulated by varying the support stiffness, using the spring and damper element parameters. The third version also incorporates the spring and damper elements as support but couples some nodes between the fish plate and rail web in vertical displacement to reduce the rail height difference caused by wheel pass-by, aiming to simulate a ‘factory-new’ condition joint. The established models were validated in terms of wheel-rail contact solution and contact force amplitude. In comparison with existing FE wheel-rail impact models the proposed models in this thesis are less time consuming and more flexible for joint angle adjustments. The second version simulating degraded joint conditions provided the most interesting findings and was used in a sensitivity analysis by varying the velocity and wheel load. The simulation results show that angled IRJs are advantageous when degradation is present, whereas in ‘new joint’ conditions the gap width plays a significant role and angled IRJs with larger gaps produce higher impact forces. Based on the results the recommendation is given to consider angled IRJs on tracks with a low maintenance scheme and further research is suggested. ... Read more

Transitiezones zorgen in de railbouwkunde al geruime tijd voor problemen. De werkelijke oorzaken van deze overgangen van regulier spoor naar een civiel kunstwerk blijven onduidelijk, terwijl de onderhoudskosten significant hoger zijn ten opzichte van andere delen van het spoor. Daarom is het interessant om meer inzicht te krijgen in deze transitiezones en welke responsies zij leveren bij een overrijdende trein.
Het doel van dit rapport is om deze responsies in kaart te brengen en vervolgens het effect van enkele maatregelen op deze responsies te toetsen. Dit leidt tot de volgende onderzoeksvraag: Hoe kunnen de responsies in een transitiezone met gebruik van de eindige-elementenmethode in een model worden verduidelijkt?
Voor het modelleren wordt gebruikgemaakt van het eindige-elementenmethodeprogramma Ansys. Als uitgangspunt voor het model wordt de labopstelling van de TU Delft genomen. In deze opstelling bestaat de transitiezone uit een bak met ballast met daaroverheen een spoorweg. Aan de uiteinden vormen stalen liggers het regulier spoor en het civiel kunstwerk.
Het gecreëerde model wordt vergeleken met de analytische Zimmermanmethode om het model te kunnen valideren. Verder geeft het Ansysmodel extra inzicht in de directe overgang van regulier spoor op het civiel kunstwerk en kunnen ontstane spanningen beter worden bepaald.
Drie mogelijke maatregelen worden aangedragen om de spanningen en verplaatsingen te verminderen in de transitiezone, waardoor er een daling in de onderhoudskosten kan worden bereikt. Deze drie maatregelen, het verbreden van dwarsliggers, het aanbrengen van railframes en het verlijmen van ballast, zijn alle gericht op de bovenbouw, omdat deze op relatief korte termijn kunnen worden geïmplementeerd.
Wat betreft de zakkingen in y-richting worden deze bij alle drie maatregelen kleiner. Hierbij zorgen de verbrede dwarsliggers en de railframes voor enkele procenten mindering van de normale zakking. Het verlijmen van ballast heeft nog meer effect. Met deze maatregel kan de maximale zakking met meer dan dertig procent worden gereduceerd.
Als er gekeken wordt naar de verandering in spanning in het ballastbed en de ondergrond als gevolg van de voorgestelde maatregelen, kan een minder eenduidig beeld worden geschetst. Sommige spanningen nemen toe, terwijl andere spanningen kleiner worden. Wel kan worden gesteld dat door het verlijmen van ballast de spanning in de ondergrond toeneemt.
Om die reden is het niet mogelijk om één maatregel te kiezen die het beste werkt om de problemen in de transitiezone op te lossen. Op basis van de zakkingen heeft het verlijmen van ballast het meeste effect, terwijl de verbrede dwarsliggers en de railframes juist zorgen voor een afname ofwel het gelijk blijven van de spanningen in het ballastbed en de ondergrond. ... Read more

Sustainable railway systems with less disturbance are highly desired. Insulated rail joint (IRJ) is one important structural component in a railway track. IRJs serve the railway system with two crucial functions: dividing track into sections for signal control and enable the detection of broken rails. An IRJ generally consists of two fishplates, insulation layers between the rails and the fishplates, and an end-post layer between two rails. The fishplates are assembled using pre-tensioned bolts. Although the IRJ plays an important role in the railway system, it introduces discontinuities in stiffness and geometry to wheel-rail rolling contact and is thus considered one of the weakest parts of the railway track. Maintenance of IRJs has been an issue of great concern for the rail operators worldwide. Over the past few years many studies have been conducted on monitoring, modelling and analysis of IRJs. Both numerical and experimental studies have been performed in order to gain better understanding of the behaviour of IRJs under static and dynamic loads. Considering that dynamic wheel-rail impacts occur at IRJs, the dynamic behaviour of IRJs should be carefully examined.
This M.Sc. thesis studies the dynamic behaviour of the IRJ experimentally and numerically. Two three-dimensional finite element (FE) track models with different types of IRJ, i.e. a new NRG-joint and normal joint, are developed. Rails, fishplates, insulation layer and sleepers are represented in the models as detailed as possible, while the rail-pads and the ballast are simplified as spring and damper elements. The NRG-joint consists of two fishplates and six pretensioned bolts, while the normal joint consists of two shorter fishplates and four bolts. Implicit FE analyses are first performed to calculate the initial stresses and displacements of the track models, which are then used as initial conditions for the explicit dynamic FE analysis. Field hammer tests are performed on the track line between Zwolle and Meppel. The tests are used on one hand to calibrate the stiffness and damping parameters involved in the rail-pad and ballast models, and on the other hand to validate the dynamic behaviour reproduced by the FE IRJ models. The comparison between the simulation and the measurements shows reasonable agreement of the results. Based on the validated FE models, optimisation strategies of the dynamic behaviour of the IRJ are proposed by a parametric study. The varied parameters include stiffness and damping of the rail-pads and the ballast as well as sleeper span. Implementation of non-uniform sleeper span seems effective for reducing pinned-pinned resonance. Finally, conclusions are drawn and recommendations for further research are made. ... Read more