The thesis includes an analysis on tension pile foundations scoped on a specific failure mechanism with the First Heinenoordtunnel chosen for a case study. The tension pile foundation installed in this tunnel is analyzed on the uplift failure mechanism due to (expected) stress corrosion. Using numerical modelling and Python algorithms, the failure mechanism is simulated. Based on the results of this analysis, recommendations for monitoring the tension pile foundations are proposed.

Currently a new Eurocode is in development where the shear capacity will be based on the Critical
Shear Crack Theory (CSCT), rather than a purely empirical model. The newly introduced formulae
provide good results overall and include the effects of bending moments on the shear capacity.
However, the formulae are known to be too conservative for prestressed continuous beams with
low amounts of shear reinforcement and severely underestimate the shear capacity. If these
formulae are applied, many existing structures would therefore no longer meet the code
requirements. New structures with prestressed continuous elements would also require more
material and it may become difficult to design efficient concrete members that meet the new code
requirements.

To prevent substantial costs, emissions and time investments, it was questioned if the design
capacity of prestressed beams near intermediate supports could be increased by changing the
location of the control section from 1d away from supports to the critical cross section. The location
of the control cross section greatly influences the shear resistance according to the CSCT calculation.
However, it is unclear how the critical cross section can be determined accurately.

In this thesis the location of the critical cross section near intermediate supports was investigated for
prestressed continuous beams with less than the minimum required shear reinforcement. A small
number of models and experiments from literature were compared. Additionally, multiple Finite
Element Analyses have been performed with a variety of settings, assuming different shear
behaviour. A plasticity approach was also investigated, where the critical cross section is found at
the location where the cracking load equals the ultimate load of a crack.

This thesis found that the reinforcement ratios, prestressing stress, shear span and effective depth
(as well as the concrete strength in lesser amount) influence the location of the critical cross section.
The experiments and models found in literature, as well as the results found using the plasticity
approach, indicate that the critical cross section for prestressed beams may be moved from 1d to
1.5d away from intermediate supports. However, due to the limitations and assumptions of the
models it would not be safe to apply this change without further validation. It is therefore
recommended that experiments are done on prestressed continuous beams with low amounts of
shear reinforcement before any changes are made to the location of the control section.

This master thesis explores the optimization of concrete through girder bridge design using a
parametric design approach, focusing on reducing material usage and optimizing for costs and environmental performance through iterative design improvements. The research addresses a critical need in the Netherlands, where numerous bridges are approaching the end of their design life and require replacement or renovation, by allowing for rapid and efficient concrete through girder bridge design.

The primary objective is to develop a comprehensive parametric model that allows for systematic evaluation and iterative optimization of design parameters. By integrating python scripting, computational algorithms and external finite elements modelling software, the study aims to provide a parametric design tool that serves as a novel approach the bridge design that yields:
-Flexible tool for structural engineers
-Iterative optimization of structural designs by:
o Minimization of material usage
o Lower environmental impact
o Lower construction costs
-Quicker design process
-Reduction of the cost of change during the design cycle

Key research features include focusing on single-span, single-track train bridges with spans of 25-45 meters and ensuring compliance with Dutch Eurocode and Prorail standards. To achieve this a comprehensive literature review is conducted and a case study of the train bridge spanning the channel is used.
The parametric model also computes an indication of environmental impact and material costs such that generated designs can be evaluated on these criteria.

To evaluate the effectiveness of the parametric model a reference design is considered that fits the scope constraints of the parametric model, namely the through girder bridge at the station of Bilthoven.
To optimize the design of this bridge three redesigns have been generated using the parametric model. The three considered redesigns are:
-Design featuring the same cross-section geometry as the reference design
-Design featuring a 'cut-out' in the centre of the cross-section to save material
-Design featuring an optimized geometry by reducing girder width
For each redesign the pre-stressing and reinforcement layout has been iteratively optimized by getting material usages as close as possible to 100%.

From the three considered redesigns, the optimal redesign manages to reduce material costs by 10.78% and environmental impact costs 11.07%. This is achieved by reducing the thickness of the girder cross-section from 1500 mm as in the reference design to 1200 mm and iteratively optimizing the reinforcement and pre-stressing layout.

The study concludes that the developed parametric model successfully optimizes concrete through girder bridge designs, resulting in significant reductions in material usage and environmental impact for a preliminary design. The model demonstrates the potential for achieving more sustainable and cost-effective bridge designs while meeting all the requirements.
By addressing the combination of structural engineering, computational modelling and sustainability, this thesis contributes to a novel approach of bridge design that can potentially change infrastructure development practices in the Netherlands.

The municipality of Ålesund aims to create a more sustainable, vibrant, and future-proof city, yet faces major challenges related to population growth, limited spatial capacity, transport congestion, and demographic imbalance. To address these issues, three interconnected cases were investigated: (1) identifying an optimal replacement for the ageing Steinvåg bridge, the only link between Hessa and the rest of the city; (2) assessing whether the Devold building in Sørsida should be demolished or reused; and (3) analysing Ålesund’s transport network to determine the potential for car traffic growth and the role of public transport in reducing congestion.

A multimodal traffic model of the city shows that the main east–west corridor experiences peak-hour congestion and cannot sustain further increases in car traffic. Meanwhile, analysis of the public transport network using GTFS data indicates that the system is robust and well-dimensioned, but significantly underutilised for reasons beyond infrastructure alone. Increasing bus frequency by 50% yields negligible ridership gains.

A multi-criteria decision analysis comparing alternative alignments for a new Hessa–Aspøya connection identifies the current bridge location, with a slightly modified orientation, as the optimal solution. A tied-arch design was selected to maintain local visual identity and meet technical requirements, with capacity sufficient even under substantial future development on Hessa. Chloride content forecasts for the existing Steinvåg bridge show that its concrete cannot be reused structurally, while steel components can be recycled.

Parallel life cycle assessments using Norwegian and European methodologies demonstrate that reusing the Devold building has significantly lower environmental impact than demolition and new construction, especially due to the high emissions associated with producing new building materials. Potential future use of the building as a concert hall, however, would introduce additional peak-hour transport strain.

Finally, a comparison of Norwegian and Dutch engineering cultures reveals differing approaches to flexibility, planning, and project duration, each with distinct advantages.

Over recent decades, advances in concrete design codes have left many existing bridges with outdated detailing and reduced nominal capacity, while traffic loads and intensities have continued to increase. Since many of these structures are now nearing the end of their service life, reducing uncertainty in their residual capacity has become critical. Structural Health Monitoring (SHM) offers a means to achieve this. This thesis investigates the applicability of Smart Aggregates (SA), a novel type of piezoelectric acoustoelastic sensor, for SHM of concrete slab bridges. A framework is proposed for SA data to decouple temperature related effects and an approach to signal data-processing challenges, in order to isolate stresses related to mechanical loading, enabling more reliable data interpretations of proof loadings and long-term monitoring. The approach is demonstrated on the Balladelaan Bridge in Amersfoort, a vintage structure with uncertain composite action between its original deck and a concrete topping layer. Signal processing was carried out using the stretching technique, which estimates relative velocity changes and cross-correlation between signals. A systematic window configuration strategy is proposed, based on wave interferometry of early-arrivals or fully diffused coda waves. A key data-processing challenge—sub-sample misalignment in the SA triggering mechanism—was identified and corrected using a confidence interval derived from reference data at the Zeeland Bridge. Temperature effects were decoupled by combining experiments and Finite Element Modeling (FEM). A negative linear relationship between temperature and wave velocity change in concrete is quantified, with velocity decreasing as temperature increases. The effect is found to be relatively more pronounced in the later coda waves compared to early-arrivals. Sub-zero temperatures indicated a non-linear temperature-velocity change relationship for freeze-thaw, important for passive monitoring applications. Simplified temperature-induced stresses, including mean temperature and linearized gradients, are evaluated using both (1) literature-based relations and (2) a parametric 2.5D finite element (FE) model, which should yield a similar result. For mean temperature changes, the literature-based approach overestimated temperature-induced stress effects compared to FE approach by an order of 10 when analyzing early-arrivals. This was caused mainly by unrepresentative assumed higher order constants relating wave velocity to stress change for the literature-based approach, and limitations of the finite element model to represent the stresses at the Balladelaan bridge. Linearized gradients showed unexpected behavior for sensor pairs at the interface between the original deck and the concrete topping layer, suggesting a complex stress state due to possible partial composite action. This is further reaffirmed by significant drops in correlation-coefficient for sensor pairs at the supports where the effect of sliding is expected. The proposed framework demonstrates how Smart Aggregates can support SHM of slab bridges, reducing uncertainty in safety assessments and extending service life through predictive maintenance and digital twin applications.

Balanced cantilever prestressed concrete box-girder bridges worldwide are known to exhibit ongoing and excessive deflections due to creep and shrinkage, which are often underestimated by conventional code-based creep and shrinkage models. These models also exhibit substantial uncertainties, leading to wide spreads in long-term structural behavior predictions and raising concerns regarding serviceability, durability, and structural safety. This study presents a computationally efficient Bayesian updating framework that integrates short- and long-term deflection measurements to improve the predictive performance of creep and shrinkage models. The framework employs Variational Bayesian Monte Carlo (VBMC) for sample-efficient posterior approximation and couples it with a zoned beam element model to accurately capture the effects of cross-sectional variability while remaining computationally efficient for direct likelihood evaluation. Application to the Rooyensteinse Bridge demonstrates that prior to updating, both fib Model Code 2020 (MC20) and RILEM B4 (B4) underestimate midspan deflections (errors of 65 % and 20.6 %, respectively) and exhibit high predictive uncertainty. Bayesian updating substantially reduces prediction errors to 4.3 % for MC20 and 1.7 % for B4, while decreasing the associated relative predictive uncertainties by 86 % and 82 %, respectively. The updated models also show that long-term prestress losses increase along the full length of the bridge, rising from 0.8 % to 7.5 % for MC20 and from 4.0 % to 19.7 % for B4 after 45 years at the hammerhead. Drying shrinkage is identified as the most underestimated parameter, with updated values increasing by factors of 3.5 (MC20) and 4.9 (B4). The perceived importance of drying shrinkage strongly depends on the number and duration of incorporated deflection measurements. Measurements from the first decade of service life were insufficient to capture the governing mechanisms responsible for the accelerated long-term deflection trend, resulting in an underestimation of the multi-deflection deflections. Although B4 still provides plausible multi-decade predictions due to its broader uncertainty bounds and flexible parameterization, MC20 becomes overconfident. Incorporating multi-decade measurements improves the accuracy of both models, allowing them to reliably reproduce the observed deflection trend. These results highlight the importance of well-structured models and the integration of long-term measurement data for reliable creep and shrinkage predictions in balanced cantilever box-girder bridges.

As materials degrade over time and traffic loads increase, monitoring the structural health of concrete infrastructures has become crucial. Structural health monitoring (SHM) and non-destructive evaluation (NDE) techniques are gaining attention for their role in maintaining the functionality and safety of these structures. One of the most effective methods is tracking stress changes in concrete, as it allows engineers to detect potential weaknesses and address them proactively, thus preventing catastrophic failures and improving safety. To monitor these changes, bulk wave-based acoustoelasticity is chosen for its promise in long-term monitoring and tracking of internal stress distributions.

However, applying bulk wave-based acoustoelasticity to concrete presents significant challenges. These challenges arise from three main areas: data processing techniques, acoustoelastic theory, and heterogeneity of concrete. First, there is limited research on data processing techniques for extracting bulk wave properties specific to concrete, resulting in a gap in understanding how these techniques apply to this material. Second, the existing acoustoelastic theory is primarily developed for scenarios where bulk waves propagate parallel or orthogonal to the principal deformation directions. This focus limits its applicability to concrete, where the principal deformation directions often vary under different loading conditions. Third, the meso-scale heterogeneity of concrete causes strong interactions between bulk waves, at frequencies of around a hundred kilohertz, and heterogeneities within the concrete. These interactions, known as scattering, significantly impact the propagation and spatial distribution of bulk waves, making interpretation challenging. This dissertation explores solutions to these challenges and offers a theoretical framework for engineers and researchers to monitor stress and strain changes in concrete using acoustoelasticity.

Our investigation into data processing techniques focuses on retrieving two categories of bulk wave properties from experiments: travel time changes and diffusive properties. We use wave interferometry techniques to measure travel time changes resulting from stress changes, comparing the wavelet cross-spectrum (WCS) technique and the stretching technique. The results show consistency in the velocity changes retrieved by both techniques. For diffusive properties like diffusivity and dissipation, we fit these proper-ties through the diffusion equation. Adjustments are made to account for boundary effects by incorporating reflected energy from so-called image sources.

We further revisit the current acoustoelastic theory to address bulk waves propagating at angles to the principal deformation directions. Our findings reveal that while shear strains have a minimal impact on longitudinal wave velocities, they significantly affect transverse wave velocities. Based on this, we propose a simplified acoustoelastic ex-pression for inclined propagating ballistic waves, primarily longitudinal, in a plane stress state, and validate it experimentally.

Understanding acoustoelastic theory alone is insufficient for interpreting travel time changes of diffuse waves in concrete; the energy ratio between longitudinal and trans-verse waves is also crucial. To address this, we propose a bulk wave energy transport model to estimate this energy ratio based on the angular frequency of bulk waves, the volume fraction of coarse aggregates, and the characteristic radius of these aggregates. The validity of the proposed model is confirmed by comparing theoretical diffusivities with experimental values, which are fitted from the diffusion equation while accounting for boundary reflections.

To investigate travel time changes of diffuse bulk waves, we integrate the previously discussed acoustoelastic theory with the bulk wave energy transport model. The energy transport model estimates the energy ratio between longitudinal and transverse waves and the time required for this ratio to equilibrate. Using Monte Carlo simulations in conjunction with acoustoelastic theory, we estimate the travel time changes for diffuse longitudinal and transverse waves. These estimates are then weighted by the energy ratio to predict travel time changes, which are compared with experimental observations retrieved using the WCS techniques.

This dissertation provides a theoretical foundation for applying bulk wave-based acoustoelasticity to concrete. Additionally, the revisited acoustoelastic theory may be applicable to other compressible, statistically isotropic solids, such as metals. The scattering theory-based model also offers a valuable tool for investigating scatterer proper-ties in concrete.

The Zeelandbrug serves as an important connection between Noord-Beveland and Schouwen-Duiveland. The bridge completed construction in 1965 using the balanced cantilever method and has been in operation for nearly 60 years. After the passage of these years, the current status of the bridge’s bearing capacity is unknown. Monitoring devices can be applied to obtain more information about the bridge’s condition and to help extend its lifespan. Hence, this study aims to investigate the application of monitoring strategies for the Zeelandbrug. As part of the process of obtaining the monitoring plan, this research also aims to gain a better understanding of the bridge’s structural behaviour. To achieve this, a linear Finite Element Model using one-dimensional beam elements was developed for the Zeelandbrug. This model was used to evaluate how the settlement of a support affects the magnitude of shear forces within the bridge’s superstructure. A structural assessment on the bridge’s superstructure was conducted, with in longitudinal direction incorporating the additional shear forces resulting from a support settlement. Through this assessment, failure modes were identified together with their associated physical parameters. Lastly, a brief investigation was performed on monitoring strategies that can be applied to monitor these parameters.

Transitioning towards a more circular construction industry is crucial for achieving climate-neutral and fully circular operations by 2030. One significant contribution to this goal is fully utilising the reuse potential of prefabricated inverted T-girders. The primary challenge lies in adapting the inverted T-girder system to enhance the circularity of the girders. To address this, a comprehensive literature review is conducted to understand the structural response and disassembly challenges associated with the system, providing valuable insights into potential improvements. This study employs a numerical model based on the Finite Element Method using DIANA FEA to assess the impact of various design adjustments, specifically the removal of end transverse diaphragms and increasing deck slab thickness. The numerical model uses horizontal and vertical curved shell elements and is subjected to several critical load cases to determine the maximum stresses for different design parameters. The results indicate that eliminating the end transverse diaphragms has minimal impact on the distribution of longitudinal bending moments and shear forces. However, it causes a localised increase in support forces by 17\%. Additionally, significant differences are observed in the deck slab, necessitating an additional capacity of 16\% for transverse bending moments and 17\% for twisting moments. The study also examines the effect of skew angles to evaluate the applicability of orthogonal system findings to skewed systems. As the skew angle decreases, a greater proportion of forces and moments is absorbed by the deck slab rather than the composite girders. However, the mutual differences between systems with and without end transverse diaphragms generally vary by up to 2.6\%, indicating that the findings for the orthogonal system are broadly applicable to skewed systems as well.

This thesis focuses on the structural behaviour of prestressed concrete girder beams with a particular emphasis on stiffness degradation near intermediate supports due to cracking, in inverted-T girders. Despite advancements in bridge engineering, there is still a lack of understanding regarding crack development along the length of the beam and its impact on stiffness, including the redistribution of forces. The thesis aims to analyse the implications of these structural changes by utilizing methodologies such as the moment-curvature diagram and Finite Element Method (FEM) models. The unique properties of the moment-curvature diagram are leveraged to accurately reproduce changes in stiffness caused by cracking. Two case studies are conducted to achieve these objectives. Case Study 1 involves comparing actual tests with FEM models, it revealed a disparity between the FEM models and actual test results. Particularly in load-deformation behaviour and stiffness variation due to crack development, this case study highlights the necessity to accurately calculate the moment regions, especially the cracking moment, which defines the moment-curvature diagram. While Case Study 2 evaluates the performance of FEM models to realistic loading conditions, including traffic loads, with some models surpassing expected performance while others failed to withstand traffic loads. Overall, the study underscores the importance of a proper methodology to accurately translate the material parameters and complex behaviours into a FEM environment.

In the Netherlands, numerous bridges face reassessment. During this assessment, it is observed that in some cases, the applied shear reinforcement (stirrups) does not meet the detailing requirement given in the national annex of the NEN-EN 1992-2. This requirement, which states that the stirrups must enclose the longitudinal reinforcement to ensure adequate anchorage, is referred by the RBK. This guideline calculates the shear capacity by combining the concrete and the stirrup contribution. However, the contribution of the stirrups can only be included when the detailing requirement is satisfied. In this research, a case study is used in which stirrups are applied that do not meet this requirement. These stirrups are expected to still contribute to the total shear capacity. Therefore, the main aim of this research is to develop a model that can predict the shear capacity by including the anchorage influence of these non conforming stirrups.

In this research, a layered approach is modeled to determine the shear capacity. This approach divides the cross section into several layers, and each of these layers is individually analyzed with the Modified Compression Field Theory (MCFT). The next step in the development of the model is to implement the anchorage behavior. There are two rebar anchorages included in this research; the straight and hooked rebar anchorage. Separate approaches are used to determine the anchorage capacities, which are based on existing experimental research. In both approaches, the axial stress in the applied shear reinforcement could be limited to these anchorage capacities.

Due to the limited availability of experimental research on reinforced concrete beams with non conforming stirrups, this research includes a constrained validation of the model. Subsequently, the shear capacity of the bridge within the case study is predicted. The first cross section in the span region, where the hooked rebar anchorage is governing. As a result of the high anchorage capacity, little influence is observed in the shear capacity of this cross section. The straight rebar anchorage of the stirrup is governing in the support region. This type of anchorage has a greater influence due to the lower anchorage capacity compared to the anchorage capacity of the hooked rebar. However, in both cases, the predicted shear capacity of the model exceeds the concrete shear capacity based on the RBK. Therefore, based on these results, it can be concluded that there is still a contribution of the non conforming stirrups to the total shear capacity.

The proposed model within this research could be used to predict the shear capacity of reinforced concrete beams with non-conforming stirrups. However, for more accurate results, it is recommended to further develop this model to overcome its current limitations. Additionally, it is recommended to conduct more experimental research on these types of beams, due to the limited amount found in literature. Finally, it should be taken into account that the model in this research uses a conservative assumption that the crack is perfectly aligned with the non-conforming stirrup.

Despite the growing popularity of diaphragm walls, there is still a lack of understanding regarding soil-concrete interaction and nonlinear behavior analysis for combining the soil and concrete part, which hinders the optimization of reinforced concrete design. This study aims to fill that gap by refining reinforced concrete design and ensuring structural integrity during construction without compromise the safety philosophy. The primary objectives are to enhance the efficiency, reliability, and sustainability of diaphragm walls through a thorough analysis of soil-concrete interactions and nonlinear behaviors.

Bridges are instrumented with joints to facilitate free thermal expansion of separate structural elements and prevent development of internal stresses due to differential settlements of the supports. In the past, mostly between the years 1960 and 1970, joints were frequently designed as half-joints, which were easy to construct and automatically maintained a level-running surface on the bridge. Additionally, half-joints can be implemented outside of the supports, which minimises the magnitude of the sagging bending moment caused by traffic loads. However, half-joints quickly started displaying signs of degradation, caused by development of a crack in one of the re-entrant corners in combination with water leakage into the joint. This crack, often buried deep inside the joint, is difficult to inspect, causing the exact state of the half-joints to often remain unknown. Another way of assessing the structural integrity of the half-joints of a bridge, is to monitor it using a structural health monitoring (SHM) system.

In this research, the measurement data of the SHM system on the Naardertrekvaart bridge is used to to evaluate its current state and serve as an early warning system for detecting damage. The SHM system, which has been collecting measurement data since 2022, includes inclinometers, displacement sensors, and temperature sensors. The research consists of an extensive data analysis procedure on two datasets of the SHM system. The first dataset contains two years of measurement data, obtained at a low measurement frequency. The second dataset contains one day of high-frequency measurement data. Next, the structural integrity of the half-joints is inferred from the measurement data using multiple custom-built FEM models in combination with manual calculations. Based on the outcome of this research, recommendations are provided on SHM systems on other half-joint bridges and improvements of the SHM system of the Naardertrekvaart bridge are proposed.

Analysis of the deformation of the bridge revealed a distinct dependence on seasonal temperature changes, presumably caused by hindered thermal contraction of the half-joints. Analysis of high-frequency measurement data showed that traffic loads significantly affect bridge deformation, with a substantial portion of rotations occurring from the support platforms' movement. Differences in rotational behaviour can be observed along the width of the bridge and a stiffness parameter is used to identify potential damage. A significant variation in stiffness can be observed at specific support locations, particularly on the east and west sides of support 6. The study highlights difficulties in using the SHM system to determine the bridge's state, suggesting improvements such as understanding traffic load magnitudes, modelling damage effects, and increasing measurement frequency. These adaptations may require cloud storage solutions. Oscillatory measurement approaches on half-joint bridges can reduce thermal influence sensitivity, mitigate the need for development of a digital twin, and enable broader monitoring with fewer sensors.

This master thesis investigates the influence of flanges on the shear capacity of reinforced non-rectangular members without shear reinforcement. The study adapts the evaluation procedure developed by Yang (2014) for rectangular cross-sections to analyze plates with holes, I-beams and T-beams.

To stop the depletion of natural resources, reduce climate change and fight biodiversity loss a circular economy in 2050 is pursued. In the upcoming years a challenging opportunity arises. Many existing bridges and viaducts with bridge decks consisting of prefabricated concrete girders have to be replaced. These girders although not designed according to circularity concepts have potential to be reused in a new structure, which is in line with the highest achievable level of circularity. However, the construction market is not ready for this innovation. So, while current research still aims at the feasibility and suitability of the girders for reuse in new structures, this research aims at the next step of preparing the construction market. This is of high relevance because it speeds up the introduction process of the innovation and thereby safes girders from demolition.

In this research the focus is on the adaptions and modifications needed in the traditional design process to ensure a more frequent implementation of reuse of existing bridge girders in new designs. After a literature review into the type of bridge girders in the Netherlands, the structural feasibility, obstacles for reuse identified by the industry, the design process and environmental impacts a design approach is developed. Simultaneously to the development of this design approach a case study is performed to give a more practical view to design aspects. In this way the approach could be verified, adapted and modified.

The design approach consists of roadmaps, possible procedures and recommendations that guides project teams through each step of the system and preliminary design. In the case study a bridge deck for a 107 [m] long bridge, divided over 5 spans with reuse of existing girders is designed. The design approach is suspectable to changes due to experiences, gained knowledge and developments in the construction industry. Therefore, it needs review over time. The design approach concentrates on inverted T-girders but can be extended and applied to other girder types as well.

In conclusion, this research provides the foundations for a changed design approach that is needed to prepare the construction market for reusing existing girders. By giving guidance to project teams, the view shifts from using new girders to reusing existing girders. This is valuable to reach the environmental objective of a circular economy in 2050.

In Amsterdam, more than 30 steel-concrete composite bridges were constructed from 1880-1960 without mechanical connectors and transverse reinforcement. Currently, there are no simplified analytical methods to determine the bearing capacity of these bridges. Thus, the bearing capacity is verified using NLFEM or oversimplified analytical calculations. This research proposes an analytical method to determine the bearing capacity of historic steel-concrete-composite bridges without mechanical connectors to avoid time-consuming FEM calculations and offers reasonable results.

An experimental and numerical study is performed on data from in situ and laboratory testing of samples from two different bridge decks from these Amsterdam bridges. The tests are accompanied by a numerical model that has been studied and adjusted to a more generalized loading case. This study determined that the exterior composite girders are critical due to their lower lateral stiffness.

An analytical model is proposed to examine the behaviour of the exterior composite girder. The model considers a 3-point bending load at midspan between the exterior composite and adjacent girder. The force distribution is described through a compatibility-based strut and tie model (C-STM). The concrete in compression is considered elastic compression struts, only limited by the ultimate load of the model. The concrete in tension is interpreted as a tensile tie, which fails when it exceeds the concrete tensile resistance. Following the failure of the tensile tie, it is assumed that a longitudinal crack propagates between the exterior composite girder and the adjacent girder. Additionally, vertical and lateral stiffness components are included in the model. These account for the flexural stiffness of the exterior and interior composite girder. The vertical stiffness is accounted for as elastic springs, and the lateral stiffness as spring beams. The interior lateral spring beam summarises all the interior composite girders' stiffness, whereas the exterior lateral spring beam only considers the exterior composite girder. Therefore, the configuration assumes that the interior spring beam is significantly stiffer than the exterior. Moreover, the stiffness of the exterior spring beam reduces when the longitudinal cracking occurs, assuming a part of the concrete fails. The C-STM is linked to the cross-section verification of longitudinal shear, biaxial bending and vertical shear resistance in two stages. Stage 1, at the load at longitudinal cracking, determines if the specimen fails at this moment, indicating that there possibly is a brittle failure. Stage 2 is after longitudinal cracking, where the steel-concrete contact perimeters have reduced, and the corresponding resistances accordingly reduce.

The failure modes obtained by the analytical model are comparable to the ones observed during the experimental testing. The analytical model showed that the bridges failed due to biaxial bending limited by partial shear interaction. One of the specimens from the testing yielded due to bending but with limited ductility. The other specimen also yielded due to bending with concrete crushing at the top concrete fibre. Further, the bearing capacities obtained from the analytical model are comparable to the failure loads from the experimental and numerical results.

The model predicts the failure modes and the bearing capacity and can therefore contribute to the assessment of the historic Amsterdam bridges, helping to reduce the assessment time of the bridges and understand their load-bearing behaviour better. Future work should focus on verifying the method by examining more bridges using FEM.

Geopolymer concrete, a relatively new building material has been suggested as an alternative to Ordinary Portland Cement (OPC) based concretes for within the building sector, due to it having a relatively low CO2 emission during production. An issue with geopolymer concrete however, is that high amounts of early age creep, shrinkage and decrease in elastic modulus over time has been observed which in conjunction with the existing research on geopolymer concrete having been predominantly conducted in laboratory settings, leads to questions about the applicability of these findings and thus the use of geopolymer concrete as a replacement for OPC based concretes in concrete structures. To address this issue, this study makes use of Fiber Bragg Grating (FBG) fiber optic sensors, placing them within reinforced steel which in turn are placed inside geopolymer concrete to obtain data that is more applicable to real world settings compared to prior findings observed within laboratory settings.
Four precast prestressed geopolymer concrete girders are produced and rebars containing FBG fiber optic sensors are placed prior to casting. Measurements before and after the release of prestressing are analysed to determine the apparent transmission length of the prestressing strands and compared to methods defined by Eurocode EN 1992-1-1. The applicability of these guidelines is evaluated, as these are intended for use with conventional concretes. The changes in strain over time, and elastic modulus changes during curing of the precast girder is monitored and analysed, focusing on the effect of time dependent changes of the concrete to the effectiveness of the prestressing forces. The girders are combined with a geopolymer concrete topping to form two beams and one slab. The beams are subject to a flexural test and a shear test respectively. The slab undergoes a cyclic loading test before being tested in two critical point load locations in two separate tests. The FBG measurements gained during the tests are evaluated using analytical methods.
The results show that the FBG fiber optic sensors integrated into steel rebar can deliver strain measurements in locations conventional strain sensors cannot be applied. The FBG data suggests that conventional concrete transmission length guidelines are applicable to this geopolymer concrete mixture. As the FBG-integrated rebars were all placed in the same location in the precast girder cross section, the strains measured by these FBGs are only representative of concrete near the core of the girder, where the concrete is not exposed to drying conditions. And because this geopolymer concrete is susceptible to drying, the difference between measurements and expected values such as the elastic modulus and the drying shrinkage can be explained by the low amount of drying that the concrete in the core of the girder experiences. Due to the positioning of rebar in the cross section of the precast girder in this study, crack initiation during the flexural test was not detected. The occurrence of cracks is detected in the measured strains as it diverged from the linear elastic model during the crack propagation phase. This shows that the cross sectional position of the sensors is important for the desired function and role of concrete in-situ FBG monitoring.
Overall, the data that the (rebar-integrated) FBG strain sensors can provide can be of great use towards the larger task of bringing geopolymer concrete structures to a real life application. In-situ FBG strain data of the precast prestressed girders provide additional information into the application of this SCGC mixture in larger scale structural elements. This data is a useful addition to the data gained through conventional methods, and results from lab testing. FBG monitoring can provide strain data from the core of structural elements, giving an insight of the behaviour during curing and (destructive) testing that is otherwise difficult to obtain.

The use of precast Reinforced Concrete has been the norm for the construction of tunnel linings for decades. However, the use of Steel Fiber Reinforced Concrete is gaining popularity due to its beneficial mechanical properties, improved sustainability, improved durability, and lowered costs compared to traditional Reinforced Concrete (RC). The amount of reinforcing steel can be reduced significantly, lowering the costs and carbon footprint of a project making it an appealing alternative. One application of SFRC is found in tunnels making use of precasted concrete segments, typically built with a Tunnel Boring Machine (TBM). This type of tunnel is found in Amsterdam, namely the
Noord/Zuidlijn: a metro line linking the north and south of the city. This project is used as a reference to perform a feasibility study on the use of SFRC and investigate its benefits.

The research involves a structural analysis of an SFRC design considering the loads and boundary conditions of the original Noord/Zuidlijn. The loads occur at different phases in the realization of the tunnel: transient, construction, and service phase. These loads can lead to various failure mechanisms, with the primary concern being tensile splitting of the concrete. Each phase is defined by a dominant component that governs its behaviour. During the transient stage, involving demoulding, stacking, and handling of the segments, the bending stresses inside the segment need to be checked. During the construction stage, the ring joints of the segments presents a weakness and need to be checked for
spalling and/or splitting of the concrete. During the service stage, the longitudinal joint needs to be checked for splitting of the concrete and the global cross sectional stresses of the lining need to be examined.

Numerical models are created to assess SFRC’s performance in the governing parts of the tunnel during the three phases, with the addition of identical RC models as a basis for comparison. The general bending and shear stresses, as well as localised splitting and spalling stresses, are investigated in both the Serviceability Limit State and Ultimate Limit State. The structural behaviour of SFRC corresponded with the characteristics found in literature, with a higher initial cracking load than RC and a more stable crack propagation due to its residual tensile strength. The peak strength of SFRC is found to be lower, but still passes all the checks. The results show that an SFRC design with the
minimum fiber content of 30 kg/m3 is sufficient for the transient and construction phases, but 40 kg/m3 is needed for the service phase. The benefits of implementing SFRC in the Noord/Zuidlijn can be quantified in a steel reduction of 60%, which would mean a decrease in steel consumption of 3050
tons. The CO2 emissions would decrease with 5500 tons, equivalent to the amount absorbed by 220.000 trees over the course of one year.

The concluding results can be used as guidance when opting for SFRC in a new bored tunnel project. The performed design checks show a governing load situation in both the construction phase and the service phase. The sufficiency of SFRC for the ring joint check during construction is governed by the
splitting force between the loading shoes of the TBM. The magnitude of this splitting force depends on the size of the TBM, the characteristics of the soil, and the depth of the tunnel. A large diameter tunnel, high-friction soil, or deep tunnel will decrease the likelihood of a design with solely fibers. The same unfavorable conditions cause large internal bending moments which could pose problems for the longitudinal joint and global cross section check. A small diameter tunnel and a tunnel constructed in stiffer soil will increase the feasibility of a design making use of solely fibers

This thesis addresses the topic of ongoing (excessive) deformations observed in balanced cantilever prestressed concrete bridges all over the world. Many authors attribute this behavior to the time-dependent phenomena of creep and shrinkage. Balanced cantilever bridges are classified as creep-sensitive structures, and for that reason, a detailed analysis of the long-term structural behavior, such as deformations and prestress losses, is recommended. However, during the design of these bridges, commonly used code-based models generally tend to underestimate the long-term creep and shrinkage effects. Additionally, various (simplifying) assumptions are made when modeling these bridges, making their actual creep and shrinkage behavior unclear.

This work aims to investigate whether the long-term effects of creep and shrinkage are indeed a plausible explanation for the excessive and ongoing deflections detected in a specific balanced cantilever bridge in the Netherlands: the Rooyensteinse Brug. This bridge, inaugurated in 1977 in Zoelen, currently exhibits a deflection at midspan of 0.43 m, more than two times what was anticipated in bridge design. To investigate this behavior, a detailed two-and-a-half-dimensional finite element model was developed, incorporating a time-dependent phased analysis accounting for the construction phases. Creep and shrinkage effects were incorporated into the concrete material model through creep compliance and shrinkage strain curves.

A sensitivity study is conducted to analyze the impact of: (i) different code-based models for creep and shrinkage, (ii) accounting for the large creep and shrinkage model uncertainties, (iii) different maturities on the creep compliance curve, and (iv) considering cross-sectional variability in the drying characteristics. The main findings showed that commonly used code-based models, including the current standard Eurocode 2, significantly underestimate the long-term (multi-decade) deflections observed in the Rooyensteinse Brug by 30%. Notably, only the RILEM B4 model (B4), considered the most theoretically grounded creep and shrinkage model, was able to capture the long-term deflection trend reasonably well. Further, acknowledging the inherent uncertainties in B4 significantly widened the range of potential deflections and prestress losses. Using the bounds of the 90% credible interval, the midspan deflections after 60 years range between 0.514 m and 2.91 m, compared to a mean of 0.895 m. The prestress losses range between 18% and 30% in the shear-critical zone, against a mean of 23%. Additionally, accounting for the cross-sectional variability in drying characteristics led to an improvement in both the short-term (first 10 years of service life) and long-term (multi-decade) deflection prediction when comparing the results to in-situ measurements, with differences of 14% and 6.1%, respectively. Based on these predictions, it is expected that the current deflection trend of the Rooyensteinse Brug will continue to decrease linearly (log-scale) for the next two decades.

This study demonstrates that a detailed finite element model incorporating time-dependent phased analysis, in combination with the RILEM B4 model and accounting for cross-sectional variability, can explain the observed behavior in the Rooyensteinse Brug. The results support the hypothesis that the long-term effects of creep and shrinkage are the cause of the ongoing trend of excessive deformations in this balanced cantilever prestressed concrete bridge.

With the continuous increase in transportation volume, bridges face the challenge of carrying higher traffic loads. As a result, bridges undergo fatigue due to repeated and increasing loads, leading to progressive deterioration of their structural reliability. While existing codes already account for several variables affecting the concrete's ability to withstand compression fatigue, some critical factors are still not considered. Furthermore, the modelling aspects of Finite Element Analysis (FEA) are often simplified or disregarded in practical applications, leading to an inaccurate estimation of fatigue life for concrete. As a result, a considerable number of bridges may be rejected for fatigue despite the possibility that they are not susceptible to this issue.
To address these issues, this thesis presents a parametric study that explores and quantifies the influence of various parameters on the fatigue life of inverted T-girder bridges, focusing on modelling aspects and material degradation. For this reason, a special case study was specifically designed to fail in fatigue within its lifespan. The fatigue analysis process employed both analytical and numerical methods, with the fatigue failure of the beams determined based on the bending failure at the beam's midspan criterion. A basic case was established as a basis for analysis, and the effect of each parameter was evaluated by incorporating it into the basic case and calculating the fatigue life of the bridge.
The analysis results demonstrate that stress distribution affecting parameters are significantly important in determining the fatigue performance of a bridge. The analysis identified that accounting for the gradual development of prestress losses, rather than instantaneous losses, and utilising area loads for vehicle modelling are critical aspects that substantially prolong the bridge's fatigue life. Furthermore, performing a historical lane configuration analysis is crucial for accurately assessing fatigue, as it significantly impacts the fatigue life of the bridge and identifies its critical components. The inclusion of material degradation caused by cyclic loading in the fatigue analysis is highly advantageous. It can even result in the bridge no longer being susceptible to fatigue. It is worth noting that accounting for the cracking of the slab in the lateral has a major negative effect on the fatigue life of the bridge. However, it is necessary to include it in the analysis to avoid an inaccurate and overly optimistic fatigue assessment. The study also provides specific equations to calculate the effect of time-dependent traffic volume on fatigue life. Lastly, the research investigated other parameters, such as the composite action of the structural components, which had a minor effect on the fatigue life of the bridge.
It is important to note that the influence percentage of most parameters cannot be generalised to all bridges, as they are contingent on specific factors unique to each case. Nevertheless, this research provides insights into the magnitude and contribution of the investigated parameters' effect on the fatigue life of concrete bridges, outlining those that must be necessarily included in the fatigue assessment.