This thesis investigates the feasibility of using concrete-filled double skin steel tubes (CFDST) as an innovative design for wind turbine towers, addressing the need for lighter, stronger, and more sustainable structures in the wind energy sector. The research is motivated by the challenges faced by the industry, including the limitations of traditional tubular steel towers, the increasing size of wind turbines, and the demand for cost-effective and environmentally friendly solutions.

The primary objective of this study is to explore whether CFDSTs could reduce steel usage while maintaining or enhancing the structural integrity of wind turbine towers, particularly in resisting local buckling under axial loads. To achieve this, both experimental and numerical investigations were conducted. The experimental phase focused on analyzing the local buckling behavior of S355 steel skins, both in single and double skin configurations, filled with high-strength concrete (C60/67). A finite element model (FEM) was developed to simulate these experiments, validate the results, and provide insights into the performance of CFDSTs under axial loading conditions.

Key findings from the study indicate that the inclusion of concrete infill significantly alters the buckling mode of the steel skins, increasing the resistance, and enhancing the post-buckling capacity. This effect was particularly pronounced in sections with higher cross-section slenderness, suggesting that CFDSTs could allow for the use of thinner steel sections without compromising structural performance, provided that optimal cross-sectional dimensions are selected. The numerical models show comparable resistance to the experimental results, though further fine-tuning of the models is necessary to enhance accuracy and better align the outcomes.

The research concludes that CFDSTs offer a promising alternative for wind turbine tower design, with the potential to achieve significant steel savings. Furthermore, suggestions for future research are presented, focusing on optimizing material selection, investigating the long-term durability of CFDSTs, and enhancing the numerical model.

This thesis explores the feasibility of drive-by health monitoring (DBHM) for railway bridges using axlebox acceleration (ABA) measurements. Considering the non-stationary nature of train vibrations passing over a bridge, a signal analysis methodology is developed including filtering and time-frequency analysis using the Continuous Wavelet Transform. A vehicle-bridge interaction model combining multi-body dynamics and Euler-Bernoulli beam elements is developed to simulate the influence of local stiffness reduction damage on ABA. Results indicate that both quasi-static and dynamic components of the ABA signal are affected by local stiffness reduction, with the quasi-static influence being more pronounced and localized. A more detailed finite element model simulating a cracked beam is developed to more accurately determine the influence of the local structural damage on the quasi-static component of the ABA signal, revealing that the crack is expected to cause a transient, localized increase in the acceleration. To comprehensively assess the feasibility of DBHM, this research integrates the simulation results with field measurements. To characterize the repeatability of ABA field measurements, measurements from three different measurement campaigns are compared to one another. It is found that the simulated impact of the local damage is overshadowed by the frequency content of the ABA signals in the time-frequency domain, indicating the difficulty to achieve direct damage detection. Alternatively, taking the advantage of DBHM in frequent monitoring, it is concluded with probabilistic analysis that reference signals under healthy conditions combined with multiple passages are essential to confidently identify structural damage. Using a case study of a damaged railway bridge, this paper illustrates both the feasibility and the inherent challenges of implementing DBHM with ABA measurements. As such, this research underscores the need for further field measurements and ABA data analysis for more reliable and accurate structural health monitoring of bridges.

Due to the transition towards a circular economy, sustainable design strategies are growing in importance. An example of such a strategy is IFD: Industrial, Flexible and Demountable design. This design strategy has been developed recently and focuses on modular designs that can be changed in shape and whose components can be demounted and reused. This thesis aims to investigate how the principles of IFD can be applied in the design of a sustainable superstructure for an overpass. The goal is to assess which structural system is best for use in a sustainable IFD overpass and to determine how the overpass can be converted into a modular overpass by focusing on connections and module dimensions. To demonstrate the potential of the IFD design, the sustainability benefits of the overpass are evaluated.

Through a review of literature on IFD and similar design strategies, guidelines were formulated that are relevant for overpasses. Based on the guidelines, designs for three structural systems were developed using a preliminary design approach. These designs were assessed on their environmental impact and compliance with IFD principles, using an Environmental Cost Indicator and Multi-Criteria Assessment respectively. Due to its good behaviour on both aspects, the Composite alternative was found to be the best.
Then, a literature study on the connections was performed to investigate the different options. The number of relevant shear connectors was reduced to four by considering the tolerances for assembly and the protrusion of connectors from the main elements of the structure. A finite-element model was made to evaluate the effects of the four different shear connectors on the structural behaviour. To be able to use the connectors in the model, an elastic limit was imposed to ensure demountability and reusability; small adjustments were made on the reported behaviour of the connectors using a parametric study. From the four remaining connectors, the Embedded Coupler Device connection without injected resin was found to be the most favourable, due to it requiring the lowest number of connectors in the serviceability limit state. For the steel girder connection, a shear-loaded bolted connection was proposed; shear keys were found to be a good solution for the deck connection. Moreover, module dimensions were determined based on sustainability considerations and IFD principles, leading to the final design.

The proposed design shows that IFD principles can successfully be applied to come to a design for an overpass. The use of a small selection of modular elements and demountable connections creates a flexible design, which complies with all the IFD principles. By application of a structural system with a low environmental impact, sustainability of the design is also accounted for.

The IFD design is competitive in situations where the overpass is extended or when it is disassembled and reassembled, since for these scenarios it ends up with the lowest overall environmental impact. This leads to the recommendation to use IFD design in situations where flexibility and reusability are advantageous.

The objective of the European Green Deal is to reduce net greenhouse gas emissions by at least 55% by 2030 and to achieve climate neutrality by 2050 [1]. Due to a growing global population and increased needs for travelling on the one hand, and progressive bans of short-haul flights by the governments on the other, the need for a more sustainable and fast means of transportation comes in high demand.

The Hyperloop transportation system has emerged as the fifth mode of transportation, offering an energy-efficient, fast alternative for freight and passenger transportation. However, to successfully establish the Hyperloop network, an extensive tube infrastructure would need to be constructed with requirements of being safe, sustainable, and cost-effective. At the time of this project, various tube designs and materials have already been examined and evaluated; given its preliminary stage of development, new design ideas are rapidly emerging. Engineers are faced with two fundamental challenges: firstly, defining safety limits, and secondly, establishing the balance between the safety, environmental footprint, and operational efficiency of hyperloop infrastructure.

The Hyperloop Skeleton tube design is the latest addition to the integral designs that holds great potential in terms of weight efficiency. The aim of this research is to determine the applicability and efficiency of the newly proposed tube design and to evaluate structural performance to imposed loads.
For the design evaluation, the study uses a numerical approach. Skeleton tube design is initially disassembled into individual components, which are analysed separately to identify potential weaknesses of the design as well as to predict their behaviour within the assembly. After that, the study conducts the analysis of the assembly. The initial design lacked rail support design; thus, a design is proposed and implemented in the model for the global analysis. Within the assembly, the research identifies critical sections and design weaknesses. In accordance with this, it proposes and analyses a new ring-to-stringer connection design. Additionally, a comparison study has been conducted with the conventional (plain) tube design, currently used at the European Hyperloop Centre (EHC) [2].

Based on numerical results, the skeleton tube design is conditionally satisfactory in terms of ultimate and serviceability limit states. The design can resist the main load case – vacuum pressure. Nevertheless, the slender components and thin plates make the tube susceptible to plate rupture or penetration if exposed to environmental actions; thus, making the hyperloop system vulnerable to accidental and impact loads. Moreover, the elastic strength capacity of rings, which are primarily in compression and are therefore critical components, is nearly reached. An initiation of local plastic response is observed, yet due to integral design, the stresses distribute among components; thus, it does not progress into a fully plastic response. Based on these findings and considering that dynamic loads are yet to be assessed, it can be projected that a strength capacity will be exceeded in further research.

The proposed steel bracket design for ring-to-stringer connection provides an alternative to welded connections. It improves stress concentrations within the ring, and considering that it is a bolted connection, further contributes to the ease of assembly, maintenance and the demountability aspect. However, the requirement for 288 such connections per 16-meter-long tube section might significantly increase the total cost of skeleton tube design.

Based on the comparison study, it is proven that the conventional tube design performs better in terms of structural performance under the considered loading conditions. However, in a controlled environment with the absence of external actions, the skeleton tube design could efficiently operate. In this case, a material efficiency of 28% can be achieved if the structure supports the rails and the pod, and up to 37.8% if the tube is solely used for vacuum pressure retention.

Emerging technologies, currently in the process of development and yet to demonstrate their contribution to a more sustainable future significantly depend on the performance and success of their initial prototypes and real-world applications. Skeleton design offers a cutting-edge design, which is on the safety – sustainability spectrum drastically leaning to the latter. A secondary protective structure is required for consideration of the skeleton design in the hyperloop application. The design can nonetheless be viable for other applications, which operate in a safe and controlled environment, with the absence of external loads. This research lays a foundation for any further research on the skeleton tube design.

To align with the objective of the European Green Deal [46] policy of achieving net-zero greenhouse gas emissions by 2050, the construction sector must transition to a circular built environment. Most of the waste in the Netherlands is related to construction and demolition waste, with the industry accounting for approximately 35% of CO₂ emissions [89]. The goal of the circular built environment is to minimise waste by reducing, reusing, recycling, and recovering materials throughout the life cycle of a product [66]. Therefore, making an impact in the construction industry can lead to a significant reduction in CO₂ emissions and contribute to the achievement of the European Green Deal [46].

This research contributes to the "reuse" component of the aforementioned circular built environment goals. Specifically, the focus is on developing a reusable connection between hollow core slabs and steel frames by implementing increased execution tolerances. Increased tolerances are necessary to allow reuse, as alignment-related problems often occur. The research consists of several parts: the design process, structural verification, experimental research on demountability, and environmental impact assessment. The design process comprises a tolerance analysis supported by a Monte Carlo simulation, variant studies, and a comprehensive qualitative trade-off analysis. After the best scoring alternative is determined, the verification part assesses the structural behaviour of the connection in terms of strength and stiffness. This is done using a combination of analytical and numerical calculations. The purpose of the experimental research is to investigate the demountability potential of the reusable connection. The final part of the research investigates the impact of the reusable connection compared to conventional connections for different lifecycle scenarios.

The research demonstrated that incorporating additional tolerances in the connection between the hollow core slab and steel frame is crucial to achieve a reusable construction. Three connection alternatives were generated that can incorporate these tolerances based on a literature review and meetings with experts in the field of building construction. The alternatives were weighted on tolerance inclusion, ease of installation, demountability potential, and costs. The best option was identified as a connection consisting of a square hollow section and a bolted shear stud encased in mortar. This alternative outperformed competitors in terms of tolerances, installation, and costs. However, the demountability potential was identified as a critical part of the connection and, therefore, was further investigated experimentally. The experiments showed an increased demountability potential in situations that include pre-treatment. Vaseline-treated specimens showed no signs of chemical bonding and better lubrication compared to oil-treated specimens, resulting in the lowest resistance and, therefore, the best demountability. The last step of the research investigated the environmental impact of the reusable connection and compared it with the conventional construction technique. Results showed that a marginal addition of 1.3% to the initial environmental impact of the superstructure results in a significant reduction over the full lifespan of the structural elements. This was attributed to the reusability of the connection and the ability to reuse structural elements in another building in a second life cycle.

From the results, it is concluded that a reusable and structurally feasible connection between hollow core slabs and integrated steel beams can be created with a small additional investment upfront, resulting in a substantially reduced environmental impact. The purpose of this study is to provide guidance and persuade decision makers, such as project developers, building owners, and government organisations, to consider implementing reusable construction methods in their real estate projects. By doing so, they can contribute to the objective of the European Green Deal [46] policies and the goal of achieving net-zero greenhouse gas emissions by 2050.

With the building and construction sector accounting for a significant portion of final energy use and emissions, and society’s increasing focus on environmental awareness and improvements, the impor- tance of sustainable construction has never been greater. The utilisation of timber in construction offers clear sustainability benefits and has the potential to replace traditional functions of concrete. One notable replacement is the use of Cross-Laminated Timber (CLT) in composite structures with steel, enabling the potential creation of greatly performing floor systems which has seen a limited amount of research. The research explores the application of Steel-CLT Composite floor systems and assesses composite beam performance as well as predictive methods for analysing their behaviour in hopes of advancing the body of knowledge on this method of environmentally friendly construction. The literature study revealed the current knowledge on steel-CLT composite floor systems and connections. Two particular floor systems, with and without the use of grout, are highlighted as well the potential for future exploration. The steel-CLT composite connection utilised in the floor system significantly impacts performance and composite action as the use of grout is concluded to increase initial-, secondary stiffness and load carrying capacity of the connection. However, restricting the use of grout can promote circular con- struction practices. In this research the behaviour of steel-CLT composite beams is predicted by the use of a numerical finite element model with shell elements and an analytical approach based on the simplified analysis of Eurocode 5(EN1995-1-1): Mechanically jointed beams. The analytical method can predict the bending stiffness with a margin of error just slightly above 10%. However, it should be noted that the analytical method incorporates an incomplete representation of the composite connection used in the beam. On the other hand, the finite element model is able to accurately capture the pre-plasticity behaviour of the steel-CLT composite beam. This is achieved by incorporating the complete load-slip behaviour of the shear connection. A parametric study was conducted to assess the importance of closely spacing composite shear connections in a steel-CLT composite beam to achieve a higher level of composite action. The study also demonstrates that by utilising connections with higher initial stiffness, secondary stiffness, and ultimate capacity, this effect can be further strengthened. As a result, the force resisted at the service- ability limit state experiences a notable boost due to the implementation of both a stronger and stiffer connection, as well as their close spacing. Shear connection position optimisation by concentration of connectors near the supports showed to have a small positive effect on beam deflection. After evaluation of steel-CLT floor systems the research concludes that a steel-CLT composite floor system can be successfully constructed, offering environmental benefits and reduced structural weight while achieving the required structural performance for the set design conditions.

Fatigue might be the governing limit state in marine structures mainly induced by the waves and wind. Therefore, using a lap joint for the shell plating to replicate the appearance of a riveted joint for a retro yacht is critical due to the limited fatigue resistance. For this joint type cracks initiated at the root, which should always be avoided due to hard detectability, might appear. Arc- and laser-welded lap joints are researched to estimate fatigue resistance and reduce the risk of root failure.
The hot spot peak stress of weld toe and weld root notches is insufficient to reflect the fatigue strength, explaining why an effective notch stress parameter is used, able to deal with both weld toe and weld root notch induced fatigue. Semi-analytical weld notch stress formulations are established in order to avoid solid finite element modelling to capture the effective notch stress. Particular attention is paid to the lap joint characteristic extreme weld notch load carrying level. A second-order weld load carrying stress formulation is introduced. Since the (laser) weld is typically small in comparison to the plate thickness, a dedicated way of weld modelling is proposed, assuming a shell finite element type of formulation, allowing to capture the far field stress for both the weld toe and weld root notch accurately.
Fatigue tests are performed to obtain the laser-welded lap joint mid-cycle fatigue resistance information, including the material characteristic length as effective notch stress coefficient. Particular attention is paid to mean (residual) stress effects in comparison to the arc-welded joint equivalent to explain the fatigue performance.
Comparing the lap joint fatigue resistance in arc-welded and laser-welded configurations to the resistance of other joint types, the results turned out to be aligned. Investigating different material characteristic parameters, either an effective point or an effective line is used. A line based parameter shows a better performance. The main reason is that the actual notch stress gradient is explicitly considered. The mean (residual) stress seems to be larger for arc-welded joints. Furthermore, the mean (residual) stress correction seems at the same time to be one reason for toe induced- rather than expected root induced failure. For arc-welded joints, the change in failure location induced by stress level dependent secondary bending moments is another reason. The fatigue resistance parameter confidence for laser-weld weld joints is relatively low in comparison to the confidence for arc-welded ones, as a result of data size: respectively ≈190 and ≈3000.
When not considering the change in secondary bending moments in the fit of a Se-N curve, the overall fit parameters and quality do not change significantly for arc-welded lap joints. However, the influence on the effective stress range is substantial and changed the value on average by 4.7 % and up to 14.7 %.
Considering only the mid-cycle fatigue resistance, laser welding is superior to arc welding when exposed to low load and response ratios resulting from the lower residual stress level. The FAT class design curve of arc-welded joints for the hot spot structural stress concept with a load and response ratio of 0.5 can be used with a mean stress correction to estimate the fatigue resistance of laser welds.

To reduce the environmental impact or cost of a civil engineering structure their designs are optimized. A promising method to optimize are iterative optimization algorithms. If both the design calculations and the iterative optimization algorithm are automated, an optimized design solution can be found within a feasible timeframe. To be able to automate the design calculations they need to be fully parameterizable. In this context it becomes interesting to research whether yet unparameterizable calculation processes can be made parameterizable. One of these processes is the determination of the locations in which the fatigue resistance has to be determined in a steel orthotropic bridge deck. This location is the location where the first fatigue crack is expected. Therefore, Antea Group requested if a study could be performed with the objective to answer the following research question:
How can the determination of the location of the first fatigue crack in the deck, at a stiffener to deck plate weld toe, be parameterized?
To answer the research question, the (in the Netherlands active) regulations are studied. Based on the regulations the process of determining fatigue damage of a point in the bridge can be understood. As well as the reason why, this process is too computational demanding and complex to be able to be applied to all points in all welds.
In response to this an alternative method is proposed. This method reduces the complexity and the computational budget that is needed, by using 1D elements instead of the currently prescribed 2D elements. To determine if this method can be used it was decided to apply it on a case study. The bridge which served as the case study was the Goereese bridge. The alternative method was applied to determine the expected distribution of fatigue damages in all welds in the case study. Based on this obtained distribution a limited number of interesting locations in the deck could be identified. At these points to regulatory required method was used to obtain results which can be compared with the alternative method.
It is concluded that the predicted location of the first fatigue crack of both methods is directly next to each other. However, the distribution of the remaining points suggest by the alternative method does not agree with the obtained results of the regulatory method. Remarkable enough, both these methods predict a location which is counter intuitive to the structural engineers participating in the research.
Therefore, the following general recommendations are given:- Research if the regulatory method, to determine the location of the first fatigue crack, can be simplified. - Research the cause(s) of the differences between the regulatory method and the alternative method. - Increase the awareness of structural engineers regarding their intuition on the location of the first fatigue crack.

Both preloaded and injected bolted connections are commonly used in steel bridges in The Netherlands. Where preloaded bolted connections are already used for a longer time, the injection of bolt holes is a method used from the 1970s onwards. Injection of bolts became a good alternative for the replacement of riveted connections. This injection increases the slip resistance of the connection by filling the clearance between the bolt and the plate. Combining both methods increases the slip resistance of a bolted connection and is therefore even more beneficial.
According to the standard NEN-EN1993-1-8 [17], it is safe to assume that the resistance of a preloaded and injected bolted connection is equal to the sum of the two individual obtained resistances from preloading and injection. The aim of this research is to validate this statement and thus investigate the resistance of a slip-critical steel-to-steel connection including preloading and/or injection.

The study addresses this manner through both experiments and numerical analysis, addressing all three types of connections. In addition, this potential of summation is considered for two different levels of preloading, implementing plastic and elastic preload preloading. These levels of preloading were considered for two reasons, embodying different applications and identifying the effect of the preload force on the resistance. Each experiment is based on a short-term testing method that is in compliance with the described method of the EN1090-2. These resistances are verified by a numerical analysis with the goal of gaining more insight into the behaviour of the connection and validation of the obtained results.

From both experimental and numerical results, it is concluded that a summation of the individual resistances overestimates the actual resistance of a preloaded and injected bolted connection when measuring at the edge of the plates. This overestimation is similar for both preload levels.
Based on these results, it is concluded that it is unsafe to assume that the resistance of a preloaded and injected bolted connection is equal to the sum of the individual resistances obtained from preloading and injection. However, this conclusion might change if a different criterion for measuring relative displacements at specific locations is implemented.

The resistance of a connection is defined at a fixed magnitude of relative displacement measured at the edge of the plate, assuming that this is representing the displacement of the bolt. However, it turned out that the assumed limit displacement of 0.15mm did not result in the same displacement at the bolt(group) for all connections due to the amount of preload force and the geometry of the plates. Therefore, it is recommended to investigate the sensibility of the measured displacements for different geometries of and preload levels in the connection.

For the renovation of the Suurhoff bridge, Arup decided to design and propose a new, innovative strengthening scheme, which improves the fatigue performance of the bridge deck and extends the design life of the bridge by at least 15 years. In this strengthening scheme, a steel plate is placed on top of the existing deck plate with a layer of epoxy in between. Preloaded injection bolts are also used to connect the strengthening plate with the deck plate. This strengthening techniques has clear advantages over the current alternatives with regard to weight, execution time, risks and flexibility in the design.
In order to better understand the behaviour of the renovated bridge deck, verify the effectiveness of the strengthening scheme and check the accuracy of the numerical models, a monitoring scheme is desirable. This is an important step in the development and optimisation of the strengthening approach, especially when the goal is to apply the scheme more often on future bridge renovation projects. To achieve this, the two research questions of this thesis are formulated as follows:
What is the effectiveness of strengthening an orthotropic steel deck with a bonded & bolted strengthening plate?
How can the behaviour of the bridge be numerically modelled to accurately capture the improved fatigue resistance?
This question will be answered through a combination of monitoring and finite element modelling. First, a monitoring scheme is set up with 16 strain gauges that are installed on the deck plate, troughs and cross girder. Quasi-static load tests are executed using a truck with known weight, both before and after the application of the strengthening scheme.
The load tests were successfully and accurately carried out and the results show a large reduction in the stress cycle. Stresses in the troughs are alleviated by 45-55% and stresses in the deck plate are reduced by 85-90%. This is largely in line with what was expected during the design.
Furthermore, the used FE models are validated so that more confidence can be gained in the design decisions. The full influence line is simulated, with the truck positioned at more than 120 longitudinal locations. The numerical modelling was able to accurately predict the shape and magnitude of the influence line generated by the truck loading. A difference in peak value between experimental and numerical results of no more than 25% was observed. The largest differences are observed for local bending in the deck plate of the unstrengthened bridge, but this is largely explained by the large sensitivity to the exact wheel position. For the strengthened bridge, a very good match is obtained in almost all locations. A difference between numerical and experimental results of no more than 10% is observed when not considering the area close to the bolts.
Close to the bolted connection (±200 mm), no accurate results can be obtained with a simplified modelling approach that uses shear springs to model the bolts. However, the obtained numerical results are conservative compared to the experimental results. Some simple modelling adjustments have been applied but are unable to significantly improve the results. A detailed modelling approach has successfully been applied in which the bolt has been modelled fully in solid elements. The preload is implemented through a dynamic relaxation phase, so the bolt force is transferred through friction of the plates without any relevant increase in computation time. Therefore, this modelling technique can relatively easily be applied in a global FE model. This modelling technique is more accurate, and analyses have successfully managed to reduce the error by 50%. However, stresses close to the bolt are still overestimated even with this advanced modelling approach and more research is needed for a complete match in this area.
In conclusion, the largely matching results reinforce the decisions from the design report. More confidence is gained in the static and fatigue design life, acknowledging the potential of this new strengthening scheme for future applications.
As recommendations for future research, more testing and design work could be carried out to further optimise the design of the strengthening scheme. Furthermore, the temperature loading can be investigated through testing and monitoring in order to reduce this critical load case. Lastly, more detailed local FE modelling around the bolted connection can help understand the behaviour in this area. This can further increase the potential of the strengthening scheme when bolts are applied in close proximity of critical fatigue details.

Welded details in orthotropic steel decks (OSD) are susceptible to fatigue cracks which are caused by local weld defects, geometric stress concentrations and residual tensile stresses. Residual tensile stresses are formed during the welding process and the distribution depends on many factors. Knowledge about the residual stress distribution is required for accurate fatigue assessment. The rib-to-crossbeam detail in the design of the new Schipholbridge does not meet the fatigue requirements according to Eurocode 3 when using a reasonable geometry. Therefore, high frequency mechanical impact (HFMI) post weld treatment will be used to improve fatigue resistance. Incorporating the residual stress distribution in fatigue life prediction models will improve their accuracy, which can lead to more favorable results which can avoid the use of HFMI. The main objective of this master thesis is to determine the accuracy of a subsequently coupled thermo-mechanical finite-element model which predicts welding induced residual stresses in a segment of an OSD. The fatigue life prediction is not included in the scope of this thesis. The accuracy of the model was determined by comparing temperature
and distortions with experimental data from three specimens consisting of a 900x400mm deck plate, a 350mm deep trapezoidal stiffener and a 600x15mm crossbeam web with a Haibach cope hole. During the welding, temperatures were recorded by a FLIR© E96 thermal camera. Welding distortions were obtained by subtracting the geometry before welding from the geometry after welding. The 3D
geometry was obtained by the Artec© LEO scanner. The scans were post processed in Artec© studio software and data was extracted by the NumPy-stl package in Python. The predicted temperature distribution and deformations corresponded well to experimental results. The maximum deviation in the
temperature distribution 1.8s after welding was 67 °C and occurred at the last position of the welding torch. The maximum deviation between predicted and measured upward displacements of the deck plate 10mm from the edge was 0.2mm, with smaller deviations on average. Due to the good correspondence
of experimental and numerical results, residual stresses were presented. On the deck plate in longitudinal direction, tensile stresses of yield strength magnitude were obtained after unclamping. At the rib-to-crossbeam connection, the stress in the direction perpendicular to the weld toe at the location of the weld toe was equal to the yield strength after unclamping. The stresses quasi-linearly go to zero through the thickness of the rib.

Torsional moments and shear stresses are not calculated correctly in the framework analysis software SCIA Engineer for cross-sections with a shear centre eccentricity. The aim of this research is to analyze and solve this problem.

The current fatigue assessment methods for naval ships are intentionally conservative. This is in part due to uncertainties in the fatigue capacity (i.e. fatigue resistance) of the ship: the nominal and hot spot structural stress incorporate implicit conservatism due to the inherent data-scatter and the Linear Damage Accumulation Model (LDAM) by Palmgren and Miner is not sufficiently accurate to assess random variable amplitude loading histories. The safe-life engineering solution to this is to employ a safety factor. This typically reduces the critical damage from 1.0 to 0.5, or even 0.2, based on engineering judgement. The main flaw of the Linear Damage Accumulation Model is that it does not properly account for the effects of the loading history. To address this flaw the non-linear probabilistic fatigue damage accumulation model by Leonetti is researched and thoroughly validated with variable amplitude fatigue data from the literature. The combination between the effective notch stress and the model from Leonetti poses significant improvements in the quality of the fatigue life predictions. The effective notch stress is used to formulate a generalised fatigue resistance curve (reducing scatter due to different geometries, hot spot types and mean stress ratios), after which the non-linear probabilistic fatigue damage accumulation model is used to work towards a generalised damage accumulation model. For the considered variable amplitude fatigue databases from literature, the Effective Notch Stress Concept (ENSC) - Non-Linear Damage Accumulation Model (NLDAM) combination proves to reduce the lifetime ratio scatter index (1:1.13, instead of 1:1.28) the most in relation to the DNV method (Hot Spot Structural Stress concept with the LDAM), allowing to reduce the implicit conservatism in the fatigue-life model.

Developments in structural engineering give rise to the ability of increasing the slenderness within the design of footbridges. However, this often results in a fundamental eigenfrequency which coincides with the step frequency range of humans on the bridge. This can lead to uncomfortable vibrations of the structure. In order to maintain the comfortability, the Dutch national annex of the Eurocode prescribes to consider a dynamic jogger load case, which is often governing for the slenderness of a design. In this thesis, a moving model for the dynamic jogger load case with the addition of human­-structure interaction (HSI) in vertical direction is considered in order to reduce conservatism. Using a simplified 1-dimensional Finite Element representation of a footbridge consisting of 4 HEA320 pro­files, a comparison is made between a moving force (MF) and a moving mass­-spring-­dashpot (MSD) model representing the jogger. Different analyses of a single jogger case are made to investigate the influence of the following simplifications: 1) applying a stationary instead of a moving dynamic load, 2) applying a load model neglecting the separation between jogger and bridge and 3) neglecting the subject variability. The Dutch national annex prescribes the use of multiple joggers during the load case. Therefore, an initial research is done on the effect of HSI on a multiple jogger case. It is found that the HSI results in a decrease of the maximum accelerations for all load cases. The effect increases when the joggers-­to-­bridge mass ratio increases. The same holds for the influence of separation. The results show that reduction of the maximum acceleration due to the addition of the HSI is generally not large enough to result in an increase of the maximum slenderness.

In the course of this thesis, a research has been conducted to the application of fracture mechanics on an othotropic steel deck (OSD). Obtaining accurate predictions of crack path and fatigue life assessment were the main objectives for this thesis. As 3D crack propagation modelling in orthotropic steel decks is an arduous task, simpler studies were examined first in order to obtain confidence for the task at hand. These studies are comprised of a through thickness crack in an asymmetrical four point bending specimen and a semi-elliptical crack in a centre cracked plate. Furthermore, studies on computational fracture mechanics and the integration of Python scripting language with Abaqus were conducted for numerical analysis of crack propagation in complex structures. The extended finite element method was used for evaluation of contour integrals of a crack with a constant mesh throughout the propagation analysis. Post-treatment of the results was applied by smoothing stress intensity factors and the shape of the crack front. Moreover, inaccurate contour integral results were excluded from analysis through extrapolation. A Python code was developed for updating the crack front for a given number of loading cycles integrated in Paris' law. The investigated crack was located at the rib-to-crossbeam joint of an OSD. Here, crack propagation occurs along the lower weld toe and in the longitudinal direction of the rib. Validation of results was obtained through experimental studies conducted at the TU Delft laboratory. The weld geometry was incorporated in the model from measurements in order to identify local stresses. Finally, results of strain gauges were used to validate the model. Measurements of the experimental crack growth were obtained at the surface of the crack only. Consequently, assumptions were made of both the depth and shape of the crack in the thickness direction of the rib. A semi-elliptical crack shape was selected with an initial crack depth of 1 mm. Initially, Paris law parameters C and m were selected as recommended by BS7910. The numerical results of crack path complied with those of experimental results, with deviations of no more than 1 mm. Both data sets show that the propagation rate remained somewhat constant. On the other hand, fatigue life assessment results showed stronger deviation. A parametric study was performed to investigate the effect of the initial crack depth. Three different cases were examined for which the initial crack depths were selected as 1, 2 and 3 mm. Varying the initial crack depth did not lead to a significant change in crack path at the surface of the rib, while the depth in the thickness direction was affected. Regarding the fatigue life assessment, the results with respect to an initial crack depth of 1 mm, complied best with experimental results. Given the strong correlation between experimental and numerical results, the methodology followed in this thesis has proven valuable regarding fatigue crack modelling. As the methodology is based on fracture mechanics, an initial crack is required prior to evaluation. Consequently, the application in engineering practices lies in re-evaluation of structures. Moreover, as the parameters in crack propagation relations have a significant influence on the fatigue life assessment, these should be carefully chosen. Therefore, more insights must be obtained regarding the selection of such parameters.

Under urban sprawl the trend of new established complex structures has rapidly increased. In this context maintenance plays a major role and monitoring of such structures represents a first important step in combating disasters. Over the last years low-cost Global Navigation Satellite System (GNSS) equipment has faced rapid and important development opening a new door to reliable and high accurate positioning applications such as structural health monitoring. This study presents a methodology for gathering, processing and analysing 1 Hz dual frequency GNSS data acquired by a network of newly released low-cost dual frequency GNSS receivers installed on a 90 metres tall steel-concrete structure in order to sense possible wind-induced displacements. At the same time, it represents one of the first studies testing the positioning capabilities of low-cost dual frequency GNSS equipment for monitoring large-scale building infrastructure. The main tools exploited in this study are PPK relative positioning together with a multipath correction procedure based on GPS satellite constellation repeatability. In addition to these, several corrections are discussed and applied on the position estimates in order to achieve millimetre position accuracy, highly needed for sensing wind-induced displacements of large-scale structures. By artificially inducing some horizontal deformations it was found that the newly released low-cost dual frequency GNSS receiver can track centimetre order permanent deformations of tall buildings. In the context of not being able to identify strong statistical correlation between possible wind-induced deformations of the case study building and and wind data patterns, the study proves that wind-induced deflections of tall structures might be traceable only if they are larger than the magnitude of the carrier phase multipath effect that is “leaking” in the position estimates.

The aim of this thesis is to propose a simple technique to estimate the maximum impact forces acting on bridge piers in the event of ship collisions. This technique is determined for Dutch commercial inland waterway ships (CEMT classes) and set up to be applied by bridge engineers to determine the required bridge pier strength. Many collision events on bridge piers have occurred in history where some led to a major failure of the bridge deck due to insufficient strength of the bridge pier. The accuracy of the Dutch guideline on calculating these impact forces (ROK 1.4) is questioned, mainly regarding the generalisation of the guideline to different ship types. Therefore, an investigation on this topic has been initiated to provide more accuracy in the estimations on bridge pier impact forces in the event of ship collisions. A dynamic nonlinear finite element model has been created using ABAQUS/Explicit to simulate the ship-bridge pier collision event. The bridge pier is assumed to be rigid and fixed, while the ship structure is assumed to dissipate all initial kinetic energy through plastic deformation (crushing of the structure). Material properties have been obtained from a test database and include rate effects. It has been concluded that the numerical calculation model is verified as stable, and results are in agreement with existing calculation methods. Numerical simulations have been performed on one class IV and two class V ship's bow structures. A relationship between initial kinetic energy levels and maximum impact force has been developed based on the results of the numerical calculations. With the established expression, the estimated impact force can be calculated for the event of a ship collision, given an initial kinetic energy level involved in the collision event. Maximum impact force values have been presented for different ship classes using this expression. For ships smaller than a medium-sized ship (CEMT IV), the impact force values are higher than is found in the current Dutch guideline. However, lower impact forces are estimated for ships larger than this medium-sized ship. This difference mainly originate from the relatively stiff response of the frontal part of the analysed ship's bows, compared to the ship's bow structure that led to the current Dutch guideline. With the proposed impact force expression, the maximum impact force on bridge piers in the event of ship collisions could be estimated with increased accuracy.

Under urban sprawl the trend of new established complex structures has rapidly increased. In this context little importance has been given to maintenance, even if this represents an important step in combating and avoiding disasters and developing improved future structural designs. Over the last years low-cost Global Navigation Satellite System (GNSS) equipment has faced rapid and important development opening a new door to reliable and high accuracy positioning applications such as structural health monitoring (SHM). This study focuses on assessing, from a geodetic perspective, the capabilities of a pair of low-cost dual frequency GNSS receivers for capturing the kinematic response of structures to wind. An experiment has been carried out with a stainless steel cantilever beam, aiming to highlight the advantages of employing a differential GNSS system for monitoring low frequency changes in the structure’s body. Hence, in this context the nominal precision of the GNSS system in East, North and Up direction of 4, 5 and 10 millimeter (1σ), was further improved to 3, 4 and 8 miilimeters in the presence of a Global Positioning System (GPS) based multipath (MP) correction. However, it is safer to consider that the true displacement retention potential of the low-cost GNSS receivers corresponds to 3 times (3σ) the aforementioned standard deviation values, resulting in slightly larger than 1 centimeter detectable horizontal displacements, and up to 2.4 centimeters vertical displacements. To support this, wind-induced beam displacements of up to 1.9 centimeters were identified and attested based on a cross correlation analysis with meteorological information. Next, the architecture of a GNSS based SHM system is proposed that can detect structural displacements in real time and rise safety alarms. Therefore, with real time kinematic (RTK) differential positioning and a position outlier and slip statistical testing procedure, a clear strategy for the estimation and identification of uni- or tri-dimensional displacement quantities in real time is proposed, to rise alarms about the magnitude and the direction of identified displacements. Hence, there is no doubt that newly released low-cost dual frequency GNSS receivers represent an alternative to high-end geodetic equipment for SHM, by offering an optimal balance between precision and cost efficiency.

For a housing project in Sirdal, Norway, a bridge is required in order to reach the construction site. Royal HaskoningDHV is interested in the possibilities that FRP composites might offer in terms of bridge design for this situation. Added to this, the fact that construction is mainly possible from one side of the river lead to the idea of an FRP cable-stayed bridge (the deck is made from FRP composite, however the cables and the pylon are respectively madefrom steel and concrete). The main span is 64 meters, which is large for an FRP bridge.Combined with its lightweight, low stiffness and structural damping, the structural response to wind excitation might be an issue. Next to designing an FRP cable-stayed bridge, this thesis therefore focuses in a second part on the dynamic behaviour to wind excitation of the bridge. To have a point of comparison with a more ’traditional’ cable-stayed bridge, in parallelto the FRP bridge, a steel-concrete alternative has been designed and analyzed. To push the comparison further, long span alternatives of the two bridges have been designed and analyzed to see their response to dynamic wind excitation. The dynamic analyses in this thesis only take buffeting (turbulence-induced vibrations) into account. Flutter (motion-induced vibrations) are considered through simple approximations from Eurocode.