Orthotropic steel decks are widely used in bridge construction due to their high strength-toweight ratio. However, they are particularly prone to fatigue cracking at welded joints, an issue intensified by increased traffic and heavier vehicles over time. This poses significant challenges for the maintenance and safety of ageing steel bridges, both in the Netherlands and internationally. This thesis investigates a novel strengthening method using blind bolted steel plates to enhance the fatigue performance of orthotropic steel decks. The central research question is: To what extent can a strengthening solution with blind bolted steel plates contribute to the extension of the fatigue life of orthotropic steel decks? A case study of the Second Van Brienenoord Bridge forms the focus of the research. Two fatigue-critical details within the heavy traffic lane are identified and targeted for strengthening. The strengthening solution involves attaching a thin steel plate to the existing deck using blind bolts, offering a lightweight and practical alternative to conventional methods such as Ultra High Performance Concrete (UHPC) overlays. A detailed finite element model of the bridge deck is developed in GSA Oasys to analyse hot spot stresses under fatigue loading before and after strengthening. A parametric model is also developed using Grasshopper to efficiently generate and assess different strengthening schemes by varying design parameters: plate thickness, bolt size, bolt spacing, number of bolt rows, and transverse bolt configuration. A comprehensive parametric study identifies plate thickness as the most influential factor in reducing hot spot stresses. Interactions between parameters, such as bolt arrangement and plate thickness, are identified. Based on these findings, a selection of promising strengthening schemes is made for further evaluation. These schemes are assessed using three criteria: fatigue life extension, added weight, and estimated installation time. Additionally, static verifications under thermal loading and heavy vehicle loading (Eurocode Load Model 2) are performed to ensure that the bolts do not fail prematurely in shear. Some schemes require denser bolt patterns at plate edges to pass these checks. The most effective schemes achieve over 60% reduction in hot spot stresses and extend fatigue life by up to 30 years, with moderate weight and relatively quick installation times. In conclusion, this research demonstrates that blind bolted steel plate strengthening can effectively enhance the fatigue performance of orthotropic steel decks, providing a cost-efficient and quick to implement solution. The use of blind bolts enhances applicability by enabling one-sided installation, even above closed stiffeners. The methodology and insights developed here can guide future applications in bridge maintenance. Recommendations for further research include experimental testing to validate bolt preload and slip resistance, more detailed fatigue damage assessments based on full stress histories, and investigation of the strengthening method’s applicability to varying deck geometries and damage levels. Practical aspects such as the interaction between deck and strengthening plate, emergency repair potential, and long-term durability should also be explored.

Climate change and the growing need for energy independence have resulted in a quickly expanding offshore wind energy industry. Foundations of these structures made from welded steel hollow sections are prone to fatigue. The wrapped composite joints omit welds, greatly increasing fatigue life. But is this technology equipped to handle the harsh offshore environment?

This research aims to gain first insight into a subject not studied in the context of the wrapped composite joint before, the effect of freeze-thaw cycles. A broad overview is created by including a vast range of experimental and numerical subjects discussing the external degradation and internal degradation, through (microscopic) surface investigation, gravimetric measurements, quasi-static tensile tests and a numerical evaluation of heat transfer and developing strains on joint geometries.

This Additional Graduation Work consists of two different fields of research: experimentally determining the linear coefficient of thermal expansion, and by Finite Element Modelling determining salt water diffusion coefficients. The research is centered around the wrapped composite joint: an innovative technology using a composite wrap connecting steel hollow sections instead of traditional welds.

Linear Coefficient of Thermal Expansion

Many steel bridges in the Netherlands, built in the 1950s and 1960s, are nearing the end of their service life, with steel bridge decks suffering from fatigue damage due to high traffic loads. Replacing these decks with Glass Fibre Reinforced Polymer (GFRP) Web-Core Sandwich Panel (WCSP) decks is a potential solution due to their superior strength-to-weight ratio and better in-plane fatigue performance.

A critical aspect of using these bridge decks safely is verifying the fatigue life of the Web-to-Flange Junctions (WFJs), which connect the webs to the facing. Fatigue damage is known to occur in such components with changing cross-sections, leading to stress concentrations. Current design codes lack verification equations or S-N curves for this component, necessitating further research.

This research investigates the static an fatigue performance of the WFJ by performing tests and identifying key parameters influencing this response. Through testing, the static bending moment resistance and the dominant failure mode are determined. Using the safe life approach, an S-N curve is generated by measuring the number of cycles until crack initiation occurred during cyclic loading.

Static tests revealed a constant rotational stiffness followed by a significant reduction due to delamination. Fatigue tests showed progressive stiffness degradation and crack propagation, with some crack retardation indicating a stabilisation phase before ultimate failure. Finite Element Modelling (FEM) accurately predicted initial stiffness but overestimated post-crack rotational stiffness, suggesting the need to incorporate additional parameters like material stiffness degradation or cohesive zone modelling.

This research identified important parameters such as waviness, web thickness, and radius affecting the response of the WFJ. However, testing did not confirm the predicted linear relationships between web thickness, radius and moment resistance as suggested by equations given by Lekhnitskii. Additionally, no direct correlation was found between waviness and moment resistance. It was observed that specimens with greater web thickness often also had higher waviness, and it is hypothesised that these parameters influence each other which would explain the non-linear relationship found from testing. Future research is needed to verify this hypothesis and include methods for quantifying the 'waviness' parameter.

This research enhances the understanding of the static and fatigue behaviour of WFJs in GFRP Web-Core Sandwich Panel bridge decks. The findings reveal that the dominant failure mode of the WFJ subjected to bending is delamination, due to out-of-plane stresses, as predicted by equations given by Lekhnitskii. Therefore, it is suggested that future design codes for FRPs incorporate these equations and delamination S-N curves to verify the fatigue safety of this component. Additionally, the WFJs were observed to be damage-tolerant, suggesting the potential for alternative design concepts to the fatigue life approach. Static tests revealed that although increased web thickness enhances the strength of the WFJs, it is also correlated with increased waviness, which is found from previous research to reduce strength. Future research could explore acceptable levels of crack growth and rotational stiffness degradation for safe bridge design, contributing to the development of design guidelines for GFRP WCSP, making it more viable to use these bridge decks in bridge renovations.

Wind turbine blades have a service life of around 20 to 25 years and are then decommissioned while generally still having excellent structural performance and high-value material properties. Currently, the recycling options for the fibre-reinforced polymer (FRP) composite components that make up the blade are limited, so most blades are either landfilled or incinerated at the End-of-Life, essentially wasting these qualities. By repurposing the blades instead, the qualities can be preserved while also lowering the environmental impact of the new structure. This research focusses on repurposing decommissioned wind turbine blades as main structural elements in traffic bridges, where the focus is on the structural design and feasibility.

The possibilities for repurposing largely depend on the type, size and condition of the specific batch of blades. Based on literature research regarding the common features of blades that are soon to be decommissioned, a custom 38-meter-long blade model is developed. Next, a variety of design options including multi-membered bridge structures have been created and arranged in an overview. By combining these options with the findings from the literature study, several designs for ‘blade bridges’ are proposed, most of which have the potential to already be realised in the upcoming years. Some of these designs are only intended for pedestrians and cyclists, while others are intended for regular road traffic. The maximum allowable spans for these bridge designs are all between 15 and 20 meters, thus confirming the large potential for repurposing blades in bridges.

Based on the structural analysis of the blade bridge designs, it can be concluded that for blade bridges as pedestrian and bicycle bridges, the natural frequency is governing. A prerequisite is that the blade-to-support connections at the aerofoil parts are designed to prevent stress concentrations, but this should be easily achievable. For road traffic bridges, it is found that the deflections are of greater importance than the natural frequencies. Also, the blades in a road traffic bridge will be highly stressed, especially locally near the supports of the aerofoil parts. These local stresses are likely to be governing, making the connection design at these supports crucial. A thorough investigation of these local stresses is therefore recommended in a real-life blade bridge project.

Orthotropic steel decks (OSDs) offer structural advantages but are highly sensitive to fatigue cracking, mainly initiated from trough-to-deck plate welds at the intersection between the trough and crossbeam. To mitigate existing fatigue cracks, a high strength concrete (HSC) overlay repair method was developed, which addresses two types of fatigue cracks but does not completely prevent root-weld crack propagation. To avoid damaging the HSC overlay by applying heating in traditional repair methods, the ‘Cold Repair’ method was developed, using a steel angle adhered to the trough-to-deck plate exterior. Recent studies suggest increased effectiveness with a carbon fiber-reinforced polymer (CFRP) angle, created by vacuum infusing carbon fiber fabrics with epoxy reason onto the OSD. However, limited knowledge exists on he use of fiber-reinforced polymer (FRP) to strengthen OSDs and control root crack growth in these weld details. This presents challenges in understanding its behaviour, material properties and design.

This study investigates CFRP-steel adhesive joints through experimental and numerical analyses. Thick-adherend shear tests (TASTs) were conducted to study the adhesive bond’s shear strength, and the failure mechanisms of these adhesive joints subjected to shear loading. Component-level three-point bending tests evaluated bond behaviour under bending loads and the structural performance of OSD strip components strengthened with a CFRP angle. Finite element (FE) models were developed to simulate the adhesive FRP-steel joint, employing both linear tied and non-linear tie-break interface conditions. Experimental and numerical results were compared to assess the FE models’ accuracy.

A comparative analysis was also performed between a full-bridge model, provided by supervising company Arup, and the component-level model developed in this thesis. Significant differences in boundary conditions, loading conditions, element formulation, and the scaling of global dimensions (apart from thicknesses) complicated precise comparisons. The component-level model used tie-break interface conditions to model adhesive interface failure, whereas the full-bridge model employed tied interface conditions, which limited its ability to predict failure.

TASTs results identified debonding between steel and primer -applied to enhance the adherend-adhesive bond- as the primary failure mode. In four samples, this debonding occurred alongside delamination of the first glass-fiber layer. The design value of the average shear bond strength was determined to be 5.42 kN. Component-level three-point bending tests consistently showed crack initiation at the outer edge of the horizontal adhesive bond at a load level of around 82 kN. Crack initiation was followed by linear behaviour up to the onset of yielding of the deck plate, after which full debonding of the horizontal leg of the Cold Repair occurred at an average load of 110 kN.

Numerical studies revealed that linear numerical modelling provides a sufficient approach to model the Cold Repair method up to the point of failure. Developed non-linear numerical models do not contribute to additional reliability of the Cold Repair method, as they were unable to accurately match observed failure behaviour and because adhesive bond failure occurs suddenly. Nonetheless, the additional capacity observed in component strips suggests that non-linear numerical modelling could extend the capacity of the Cold Repair method if its design allows for damage. To improve the accuracy of adhesive bond failure modelling, further experiments, including fracture mechanics tests, are recommended to determine essential adhesive properties, such as fracture toughness.

Between the 1950’s and 1970s, a large increase in bridge construction was realized accompanying a large increase in infrastructure. The increase in traffic intensity and weight results in that many of these bridges are now in need of reevaluation, possibly resulting in renovation or renewal. Meanwhile human-caused adverse environmental effects are increasingly impacting the world, of which the infrastructure sector is a large contributor.
This thesis provides a study into more sustainable renewal projects. The objective of this study is to provide a design which will increase the sustainability of renewing bascule bridges. The approach for this study is to:
• Literature review to set a scientific basis for this thesis project.
• Design study to explore the possibilities for bridge leaf design.
• Summary, conclusions, and recommendations to conclude the research project.
To design a more sustainable alternative the “Design for sustainable infrastructure” is followed. The ambitions identified following the “Ambition web” methodology highlights a great influence of a structural engineer in environmental sustainability. Key opportunities to increase environmental sustainability include reusing structural elements, maintaining or reducing the mass of the bridge leaf and designing the structure to fit inside the footprint of the current bridge.
The design process starts by applying “Circular design principles” to design a variant which reuses most of the available elements. Following variants increasingly differ from the current structure by removing elements, changing the materials from of the elements, or using free forming opportunities of FRP to come to new designs.
The sustainability performance is strongly dependent on the current state of the structure. Reusing the main structure and renewing only the deck can reduce the environmental impact of the bridge leaf by up to 53%, while not increasing the mass or requiring more space. Redesigning the entire structure with a full FRP structure can reduce the environmental impact by up to 48% and could reduce the mass of the bridge leaf by up to 33%. For both scenarios, the use of FRP, with a balsa core and partly recycled resins, was thus beneficial for the sustainability of a bascule bridge renewal project.

Orthotropic steel decks (OSDs) are commonly used in bridge construction due to their material efficiency and strength. However, fatigue issues in welded joints remain a concern. Fatigue cracks often occur due to high stress concentrations, especially under heavy traffic loads. Current approaches of determining damage in a bridge are limited by the computational demands of Finite Element (FE) models to calculate stresses and the complexity of the fatigue verification. Consequently, there has been limited exploration of parametric optimization for OSDs. This research seeks to address this gap by developing a parametric model to assess the fatigue performance of OSDs according to the ROK version 2.0, the new Dutch Guideline, additionally focusing on identifying the influence of key design parameters through a parameter sensitivity analysis (PSA). This study aims to provide insights for optimizing OSDs to enhance fatigue resistance and design. Thereby aiming to increase material efficiency about OSDs and creating a parametric framework to determine damage in an OSD.

This resulted in the following research question: How can a parametric model be developed to assess the fatigue performance of Orthotropic Steel Deck bridges and what insights can be gained from analyzing the influence of key design parameters?

To answer this question, in part 1 a literature study is performed. This began by reviewing the theory of the OSD’s and fatigue, identifying the critical fatigue parameters which were expected to influence the incorporated directly ridden details. Furthermore, the Dutch regulations and state-of-the-art about automatizing of fatigue verifications were explored, after which a parametric model is developed.

Part 2 began by developing this model. Simplifications in the mesh and loading scheme are tested and applied to ensure the model is fast and sufficiently accurate. Utilizing various mesh sizes in different regions helps to reduce computation time by almost 300% while maintaining accuracy. Additionally incorporating symmetry in the loading scheme further reduces the computational time by about 127%. With this model, the first part of the main research question is answered. The model is used to find the governing details in the bridge within the design domain of the ROK [2]. The governing details are: the crack initiating at the weld toe located at the intersection of the trough and the deckplate, and the crack initiating at the weld root located at the intersection between the deckplate, trough and crossbeam. Which are respectively detail 1A and 1C of the ROK[2]. After this, a benchmark model is found to start the PSA and a sensitivity analysis is conducted for these previously mentioned details by systematically altering one parameter at a time (OAT).

Results of the PSA are distinguished for the two aforementioned details. For detail 1C, the deckplate thickness and trough top width influence the damage of the detail primarily, represented by respectively an exponential function and second order polynomial. The crossbeam thickness influences the damage by maximally 30% of the damage number of the benchmark, while this parameter is not included in the analytical solution. Other included parameters show small or negligible influence on the damage of detail 1C. The governing load position within the design domain is the transversal load distribution exactly above the middle of a trough. Furthermore, a difference in stiffness exists between two trough legs of the same
trough for detail 1C, significantly influencing the damage. The governing transversal location of detail 1C is at the trough leg closest to the main girder.

For detail 1A, by far the most influential parameter on the damage of this detail is the deckplate thickness, having a exponential influence. The trough center-to-center distance has the second greatest influence on the damage, this can be represented by a second order polynomial. The top trough width and crossbeam center-to-center account for a maximum influence of the damage number of 20% of the benchmark damage number. The influence of the other included parameters were small or negligible. The governing transversal location of detail 1A is, similarly to 1C, at the trough leg closest to the main girder.

The validation of the model shows a great difference in the difference in damage numbers obtained from version 2.0 of the ROK in comparison with version 1.4. Validation of the Goereese bridges therefore show damage numbers greater than 1 for the 2 aforementioned details. It is suggested to show extra attention to bridges designed with ROK version 1.4, or earlier versions, and to repair occurring cracks in a way that the local damage complies with the verification of ROK version 2.0. The parametric tool can play a useful part in this when expanded. Another future use case can be to support the goal of the Rijkswaterstaat of replacing the current labor-intensive fatigue calculation method with a table that outlines the dimensions of OSDs, by generating a large amount of data.

Steel jacket support structures for offshore wind turbine towers made of circular hollow sections (CHS) are becoming a competitive solution compared to monopiles in deeper waters. The current limitation to improving the durability and cost-effectiveness of the CHS structures is the low fatigue endurance of their welded joints. Fatigue-driven design of such structures usually leads to thicker profiles of steel members as well as costly welding of joints. Due to excellent corrosion and fatigue endurance, high strength-to-weight ratio, easy and locally made fabrication, fibre-reinforced polymer (FRP) composite materials have been widely used to strengthen welded CHS joints. Although this strengthening technique can enhance the resistance and fatigue performance of the welded CHS joints, welding still serves as the main way for load transferring in the joints. Therefore, welds remain the source of stress concentration and brittle fatigue failure. Recently, an innovative joining technique, wrapped composite joint, has been proposed at TU Delft. In this joint, the CHS members are connected through the composite wrap. Loads are transferred at the bonded composite-to-steel interface, and welding is completely avoided. While monotonic tensile tests have shown the superior stiffness and resistance of the wrapped composite joint over its welded counterparts, the fatigue performance of the joint still needs to be investigated.

As the first investigation of the fatigue behaviour of the wrapped composite joints, the present study focuses on the most unfavourable failure mode, debonding at the composite-to-steel interface. A typical joint geometry in the jacket support structures, the K-K joint, is chosen as the research object, which is simplified to be the uniplanar X-joint. The general objective is to accomplish knowledge sufficient to predict the debonding behaviour of CHS-wrapped composite X-joints under tensile cyclic loads.

To achieve that goal, the present work starts from the interface level, where the fatigue crack growth (FCG) properties at the composite-to-steel interface are characterised through fracture mechanics experiments, i.e. 4-point bending end notched flexure (4ENF) tests. The steel surface of the specimens is prepared with different roughness levels, and its impact on FCG properties is investigated. The obtained FCG properties provide the basis for predicting crack growth at the joint level. In the wrapped composite joints, friction exists at the composite-to-steel interface due to the confinement by the composite wrap, which may retard the crack growth. This phenomenon is quantified in cyclic tests on joints with simple geometry, i.e. the axial splice joint (A-joint), where the debonding crack growth is monitored through the 3D digital image correlation (DIC) system. At the joint level, tensile cyclic tests are conducted on the wrapped composite X-joints with different surface roughness and at different scales. Post-fatigue static tests are conducted to check the influence of cyclic loads on the residual resistance of the joints. Using the finite element model, the methodology to predict the crack growth and stiffness degradation of the wrapped composite joints is established, which can consider the interaction between debonding on the chord and brace members. The prediction methodology is validated against the test results and used in a probabilistic analysis to explain and reproduce the scattering test results. Finally, the failure criterion of the joints under cyclic loads is proposed to establish the design S-N curves.

The present study found that the surface roughness of the steel tube plays an important role in the FCG properties of the composite-to-steel interface. A minor increase of the surface roughness can significantly improve the joint’s fatigue performance, with the parameter C of the Paris curve decreasing over magnitudes. At the joint level, the wrapped composite X-joints exhibited steady stiffness degradation during the tests due to debonding propagation at the composite-to-steel interface. Joints with reduced surface roughness show deteriorated fatigue performance but still have longer fatigue life over the welded ones. By including friction at the interface, the finite element model gives reduced strain energy release rates (SERR) at the crack front as the crack grows. Thus, the main source of the crack growth retardation is explained and can be quantified. The numerical results match well with test results of X-joints considering different surface roughness, different load levels and scales, and the relationship between debonding on the chord and braces is obtained. By studying the variability of surface roughness and FCG properties, the probabilistic analysis can reproduce scattering of the test results. Finally, the design S-N curves are obtained based on the experimental and numerical results, taking 5% resistance reduction as the failure criterion.

The present study provides a methodology for characterising and predicting fatigue debonding behaviour, not only for wrapped composite joints but also for other large-scale bonded joints with complex geometry, enhancing the application of bonded joints in engineering structures.

As many bridges in the Netherlands are past their design-life and yet still have well-functioning steel superstructures, their bridge decks are often due to be replaced. FRP panels are promising alternatives to concrete decks for these renovation works due to their low density, fast on-site construction time, and excellent acoustic and thermal properties. Many of these bridges are originally designed with hybrid interactions occurring at the connection level. Multiple connection types exist to ensure hybrid interaction with FRP decks. However, there is a gap in this field concerning a rapidly demountable connection able to transfer shear forces at girders with oversized holes. The injected reinforced resin connector is designed and aimed at achieving hybrid interaction through combined injection and preloading of the connector. The aim of this thesis is to find a viable design for this connection, and to test the connection under local compressive wheel loads. be able to design the connector and test it according to standards as expected to occur in real bridge applications, a FE-model of the bridge Nieuw-Vossemeer is made to assess expected loadlevels in the connection. The result is a combined list of loadlevels and geometrical tolerances that the connection will have to be able to sustain or perform under. Based on the resulting design requirements a main design is proposed. Here a steel bolt is embedded in the bridge deck and held in place by injection with reinforced resin. A steel plate separates the bridge deck from the girder flange, and creates a full steel clamping package. Multiple design alternatives are tested by the use of FE-models, where the variable is the type of steel plate used between the bridge
deck and the girder flange. The most viable design to continue experimental tests with is selected by its stiffness, ultimate resistance, and a qualitative assessment regarding expected cyclic endurance. The best performing concept is a steel plate with a spherical bottom, a diameter of 150mm and maximum thickness of 20mm. Extra FE-analyses are performed on a local scale, and take into account positional deviations from the most ideal situation. In addition a series of two static and two cyclic experiments has been performed. Apart from finding their respective resistances, the failure modes are assessed and compared together with the numerical analysis. The static tests show an ultimate resistance of 501kN, the numerical analysis shows a resistance of 498kN. Both the static tests and the numerical analysis failed ultimately due to delamination in the bottom facing of the FRP, the cyclic tests failed under a similar failure mode in the bottom FRP flange. On loading ranges with R = 0.1 it is found that the primary failure mode is a horizontal crack opening up in the bottom FRP flange, which propagates into the webs. The connection withstood 2 million cycles at 9kN - 90kN without damage. Subsequently, two different loadranges were applied to the two different tests, which failed after 394 thousand cycles at 13.5kN - 135kN and 34 thousand cycles at 18kN - 180kN. It is concluded that the spherical plate is able to function as a coverplate and withstands rotations, displacements and the required loadlevels as expected in bridge applications. The primary recommendation is to continue performing tests with a similar plate with a thickness of 15mm, as the current design overshoots the required resistance significantly.
The results show that the design is well able to sustain the required local compressive wheel loads, both in ultimate and cyclic resistance. With the ability to (de)mount these FRP panels quickly on-site, two main goals have been reached. Firstly, this brings the use of FRP panels in infrastructure closer, leading to reduced loads onto steel superstructures of existing bridges (and hence an extended lifetime). Secondly, a fundamental step has been set towards modular bridge design, where during failure only specific panels of the system have to be replaced. Together these developments can lead to a reduced impact of the construction industry on the environment.

This research investigates the feasibility and potential of utilizing BFRP floors in modular buildings as a low environmental impact and cost-effective alternative to conventional floors. A modular building is introduced as a case study, the Natural Pavilion in Almere, to bring focus to the research and set a baseline for the requirements of the BFRP floor. A second case study, the bio-composite bridge in Ritsumasyl, is introduced to utilize its comprehensive dataset of material properties representing the state-of-the-art BFRP. Using the two case studies, two design solutions, a one-way and two-way floor, are developed.

Comparing the designed BFRP floor to conventional floors such as cross-laminated timber, concrete hollow core slab, and concrete flat slab, several conclusions can be drawn:

(1) The construction height of BFRP floors is similar to that of conventional floors. The weight of the floor is similar to a CLT floor, while a concrete floor is 6-8 times heavier. Design optimization is possible, and the amount of BFRP material utilized can be reduced by up to 21% for the one-way floor and 19% for the two-way floor. Additionally, the floor design proposed in this thesis is intended for buildings with a design life of 15 years and no specific fire resistance requirements. For structures with a design life of 50 years, it is imperative to increase the floor height to meet deflection criteria. Further research on fire resistance and additional measures is necessary to extend applicability beyond single-compartment buildings and terrace housing.

(2) The environmental impact of a BFRP floor, assessed in terms of Global Warming Potential through a Life Cycle Analysis encompassing stages A1-A5, is found to be twice that of a concrete floor. Through optimization of the floor design and reduction of BFRP material usage, it is possible to achieve a reduction in CO2 emissions of approximately 10%. Nevertheless, in the current state-of-the-art, BFRP floors exhibit a higher environmental impact than conventional flooring systems. The use of resin and the production process are the primary contributors to CO2 emissions. The contribution from the production process requires nuance, as results heavily depend on the data source. Factors such as manufacturing techniques and production scale significantly affect this impact. By reducing the impact of the resin and production techniques while also exploring end-of-life possibilities for 100% bio-based BFRP, the environmental impact of BFRP floors holds potential for the future.

(3) The floor cost is nearly twice as high as a comparable CLT floor. This can be attributed to introducing new design solutions with a sustainability focus, often resulting in increased costs due to lower demand, higher material and design expenses, and limited production scale. Even though current costs are much higher for BFRP floors than for conventional floors, there is potential for BFRP floors to become more cost-effective and competitive in the future, especially when the environmental impact is reduced. It is difficult to estimate how the price of BFRP floors would change over time, and therefore, it has not been taken into account in the results.

Hybrid structures consisting of FRP(fiber reinforce polymer) composite decks
connected to a steel girder superstructure are gaining more attention by combining the stiffness of steel members with good fatigue endurance and high strength to weight ratio of FRP. However, when composite material FRP is exposed to elevated temperature, delamination and strength reduction could appear due to low transition temperature of fiber and resin. As a result, predicting the temperature of the FRP bridge deck becomes a preliminary requirement for the further study of the FRP bridge deck.
This research is trying to simulate the heat transfer process of the FRP bridge
deck and predict the temperature changing process when it is exposed to natural environment. To reach this goal, experiment and FEM(finite element model) are used as main methods. By detecting temperature change history of the FRP bridge deck specimen during hot weathers in Delft, Netherlands, the maximum temperature and heat transfer process of the FRP bridge deck could be studied. On the basis of experimental results, an detailed FEM in Abaqus is built up to simulate the heat transfer process of the specimen used in the experiment. After validating the accuracy of FEM result with experimental data, the FEM is used to predict the temperature of FRP bridge deck that exposed to natural environment in the hottest weather of Netherlands.
In conclusion, the results shows that the temperature of FRP structures could be
well predicted which only has 10.5% variance predicting the maximum temperature on the top surface of the specimen and high accuracy of 6% predicting the average temperature of the FRP panels along the thickness. It also has high accuracy of 3.5% predicting the maximum web-core temperature difference. The only insufficient part is that the average temperature difference of web-core has a deviation of 21% with the experimental data. As FRP panels make up the web and flange of the bridge deck which are the main structural parts that bear the stresses, the inaccuracy of predicting temperature of the core is acceptable.

The increasing traffic load on highway bridges provides a need for replacement or improvement of the bridge decks. The design of a new bridge deck using fibre-reinforced polymer (FRP) bridge decks raises questions on the connection of a FRP bridge deck to a steel superstructure. At the Tu Delft a bolted connector injected with steel reinforced resin (iSRR) is developed for the connections between steel superstructure and FRP bridge deck. Steel reinforce resin (SRR) is a combination of steel shot (SS) and resin. The steel shot is added to achieve higher stiffness and reduce the total production cost. The iSRR connection can be produced using multiple methods. For all production methods, the SRR in the connector is produced by pouring SS around the bolt followed by the injection of the resin. The iSRR connector should accompany the fatigue resistance of the FRP bridge deck. A better understanding of crack propagation can help to increase the life expectancy of iSRR connections. However, no standardized method for the testing of crack propagation in SRR exists. This research attempts to find a crack propagation testing method for SRR by investigating the use of compact tension (CT) and semi-circle bending (SCB) testing for the SRR material. For the production 5 different casting methods were compared. From these methods, the closed mould injection casting and ring mould injection casting showed the most promising production method for the production of complicated forms in SRR. From this testing the need to use modified forms of CT and SCB was found, resulting in the use of a doubly tapered compact tension specimen (2TCT) and the design of the short tapered notched beam specimen (STNB). The modified specimen forms are tested under varying loading types. The 2TCT specimen is tested under load controlled, and displacement controlled loading. From this, the incremental increasing loading type was suggested. This loading type was used in the testing of STNB specimens. Lastly with the use of FEA the stress intensity factors for the modified test forms were validated. The validation was done on the analytical formulas provided by literature for the unmodified forms. From this research, it can be concluded that the closed mould injection casting and ring mould injection both achieve good results for the production of complicated shapes with SRR. The incremental increasing displacement loading method leads to more stable crack growth. The 3 point bending testing type leads to the most promising results for crack propagation. With a linear correlation in the small range of K = 20-60 resulting in a Paris Law with 𝐶 = 4.3𝑒 − 7 and 𝑚 = 2.41. It is recommended for further crack propagation testing to produce specimens with the least amount of voids. The voids are expected to have a high contribution to the big spread of data found during the testing. For better insight, the voids in the tested specimens could also be investigated.

This research is about which geometry of FRP slabs is the most optimal, in terms of costs, to use for a given load and boundary conditions taking the occurring uplift bolt forces into account. The first part of the report focuses on the calculation of the uplift forces in the bolted connections caused by the moving loads. For this, first a detailed numerical model is made in Abaqus. Based on this most detailed numerical model, different simplifications are made to make the calculations easier and less time-consuming. Numerical models with linear bolts instead of non-linear bolts and with load superposition using a one-wheel load instead of a complete vehicle are considered. Next to this, equivalent material properties are calculated to make a model with an orthotropic deck plate instead of modeled geometry of skins and webs. For the numerical model with this orthotropic deck, the same simplifications are applied. Next to the numerical models, different analytical beam and plate models are considered. All different numerical and analytical models made, are compared on possibilities, calculation and modeling time and accuracy. Based on the comparison between the models and the capacity of the connections, it is concluded that the uplift design of the bolted connections does not need to be taken into account in the optimization of the slabs.

The second part of the graduation work is about the optimization of the FRP slabs considering the global behavior of the deck, for which a genetic algorithm is used to detect the most optimal geometry. The most important parameters for the design are the height of the deck, the spacing of the webs and the layup of the topskin, bottomskin and webs. The layup of the different elements is dependent on the number of plies, the ply orientation and the overlapping length. During the optimization process, design and initial (global) strength, stability and stiffness checks are performed. First, optimization is done for the same deck that is considered in part one of the research. Next to this case, different cases for the distance between the supports are considered for which standardization is done with respect to engineering and production of the slabs.

Based on the performed research it is concluded that the uplift bolt forces are in a range of 0.5 to 21.5 kN. Simplifications can be done by the use of an orthotropic deck with equivalent material properties. The maximum difference using this simplification is 2.9 kN, while the calculation time needed is reduced by a factor of 4-5. Other simplifications that can be done are the use of linear bolts and/or load superposition. Using linear bolts gives a maximum difference of 0.5 kN and load superposition a maximum difference of 0.3 kN, both without an improvement of the calculation time. The optimal geometry for different boundary conditions is given as a standard design with a variable number of plies for the topskin and a variable height based on intervals for the distance between the supports.

In the past years, the safety of steel railway bridges has been questioned due to the coped beam connection sensitivity to fatigue and fatigue crack appearance. To ensure the safety of these railway bridges, the propagation of the fatigue crack needs to be analysed by performing regular inspection on the bridges. The frequency of these is required by the defined inspection intervals, which are based on the critical crack length and the number of loading cycles leading to this crack length. Laboratory tests and measurements on the bridges have been performed in the past to define inspection intervals, but had given only an approximation of the real situation. By creating a finite element model of a coped beam, a crack initiation and propagation analysis can be performed. This analysis provides an indication after how many loading cycles the crack will reach a critical length and guides towards revised inspection intervals.

In this thesis, the objective is to take the first steps towards the revised inspection interval by performing a finite element analysis of the crack propagation of steel railway bridges. More specifically, this means an finite element analysis of the coped beam with extended finite element method.

To achieve this goal, first, the location of the fatigue crack initiation has been investigated to understand where exactly in the cope the crack starts. This was performed by creating a local 3D linear elastic FE-model of the coped beam based on the boundary conditions, geometry, and loading from laboratory tests performed by Michael C.H. Yam and J.J. Roger Cheng. The the longitudinal stresses of the model were compared with stresses measured during the laboratory test to validate the crack initiation model. After the model was validated, the location of crack initiation was determined by identifying the location of the peak stresses.

After completion of the crack initiation analysis, the crack propagation analysis can commence. For this, the FE-model was transformed from the crack initiation to the crack propagation model. In the same manner as with the crack initiation model, the propagation model has been based on the boundary conditions, geometry, and loading from the laboratory test. Since no path of the crack was registered during these laboratory tests, and thus could not be implemented in the model, a method for crack propagation analysis called extended finite element method (XFEM) has been used. The accuracy of this method has been confirmed by validating the stress intensity factor (SIF) values obtained for stationary cracks with three different mesh topologies and comparing the results with results from two established methods; J-integral and VCCT.

After the validation of the crack propagation model, a sensitivity study was performed to understand the potential influence of modelling decisions on the number of load cycles versus crack length relation. With the mesh sensitivity analysis, a linear trend has been obtained for models with matching number of elements through the thickness. For the initial crack size sensitivity analysis, the effect of the number of elements through the thickness and the effect of mesh topology have been investigated. One element through the thickness and parallel mesh topology led to lower variation in the results.

Additionally, a new value for the previously assumed Paris law coefficient C has been obtained by calibrating the number of cycles versus the crack length curve from FE-model to match the laboratory test results.

In conclusion, this research provides recommendations for modelling crack propagation in a coped beam. The results are more reliable when keeping at least five finely meshed elements around the crack tip, using a parallel mesh topology, and using one element through the thickness. New value for the C coefficient from the Paris law has been suggested based on this research.

The next step in this research is a continuation of the crack propagation model analysis to reduce the variation in the results. Furthermore, different loading positions and expansion from a simply supported beam model to a model with multiple spans should be analysed to bring us one step closer to the ultimate goal of redefining the inspection interval for coped beam steel bridges based on the models.

This report investigates the influence of joint stiffness on the eigenfrequencies of offshore wind turbine supporting jacket structures. The joint is investigated individually, within the context of a jacket structure, and within the context of the entire offshore wind turbine structure. These analyses were specifically conducted for the case of a 10MW wind turbine jacket support structure. This report aims to present an analysis method that can represent the joints of jacket support structures for offshore wind turbines with high fidelity while also ensuring low computational cost during the analyses. The joint stiffness is captured through an implementation of joint submodelling by applying the Craig-Bampton reduction technique. Along with this, the report serves to provide a comparison of innovative wrapped composite joints and traditional welded joints when applied to a 10MW wind turbine. The wrapped composite joint was developed by Dr. Marko Pavlović at the Delft University of Technology, and it was investigated due to its superior fatigue performance compared to welded joint alternatives.
Two sets of analyses were conducted: the jacket analysed by itself, and the jacket analysed along with the tower, turbine, and piles (to be referred to as the ”offshore wind turbine”). Natural frequency analyses were conducted for the jacket and for the offshore wind turbine for the different joint types. It was found that for the jacket and for the entire offshore wind turbine, the models with welded joints had the lowest natural frequencies, the models with wrapped composite joints had the second lowest natural frequencies, and the models with rigid joints had the highest natural frequencies when compared to their respective counterparts.
In conclusion, both the application of the wrapped composite joints and the application of the analysis method of submodelling joints of the jacket are beneficial for solving issues related to the construction of jacket support structures for large wind turbines.

The increase in road traffic intensity and loading capacity of a truck over the last decades causes fatigue problems in existing bridges built in the 1960s and 1970s. For steel bridges, this means that the deck structure does not meet the current demands. A solution would be to replace these existing deck structures with Glas Fibre-Reinforced Polymer (GFRP) sandwich webcore deck panels. However, the ministry of infrastructure in the Netherlands has voiced its concern about the fatigue performance and displacements of these deck panels under the high traffic load and intensity. Furthermore, the knowledge about the fatigue performance of GFRP deck panels, applied in the main road network, is still limited. At the time of writing this report, the technical committee, CEN/TC 250 (responsible for developing structural eurocodes), establishes a technical design specification for Fibre-Reinforced Polymer (FRP) structures. This technical specification requires full-scale fatigue testing due to the complex failure modes that can occur. General fatigue damage summation methods like Palmgren-
Miner [30, 41] are not allowed by this technical specification. This report discusses the development of Virtual Fatigue Stiffness Simulation (ViFaSS), a numerical non-linear fatigue stiffness reduction model that can predict the fatigue performance of in-plane stress dominated Glass Fibre-Reinforced Polymer components, with a wide range of lay-up compositions, based on existing knowledge and experiments, including the damage development under multi-axial stress states and stress redistribution. The damage development includes damage accumulation dependency on damage history and damage development dependency on the load type, e.g. Tension-Tension (T-T) or Compression-Compression (C-C). With the low utilisation of the material strength in civil engineering applications, the research is limited to the stiffness degradation of the material. The numerical model is coupled with the Finite Element (FE) software SOFiSTiK where the component is modelled with shell finite elements. The fatigue material response is characterised on a unidirectional ply level based on principal ply directions and based on experimental results from the Optidat program [36]. The coupon response predicted by ViFaSS for constant amplitude T-T and bending fatigue loading was in reasonable agreement with experimental results. For future work it is recommended to extended the model with the ability to use non-linear material behaviour and to include the strength degradation caused by fatigue.

Fiber Reinforced Polymer (FRP) has increased rapidly in popularity in the past few decades. The material's advantageous properties, such as a high strength-to-weight ratio and low required maintenance, gave rise to its popularity in multiple major engineering branches. Buckling behaviour develops due to the notably low stiffness-to-strength ratio and the usual high slenderness of FRP plates. The occurrence of initial imperfections increases the tendency of the material to buckle. The load-carrying capacity of structures with post-buckling behaviour can be determined with progressive failure analysis, which requires a damage model that characterises the onset and evolution of damage. In Abaqus, the Hashin damage model is implemented by default, which considers the four failure modes of the material. Numerical analysis of strain-softening materials with local damage leads to deformation localisation in a single element: a finer mesh will decrease the amount of energy dissipated. To prevent this localisation into arbitrarily small regions, the stress is related to the deformation of a finite volume. The damage evolution is described with a stress-displacement response instead of a stress-strain response. The energy needed to open a unit area of the crack, the fracture energy, is defined as a material parameter and depends on the mesh size of the model. The assessment of fracture energy properties in composite materials is challenging due to specimen geometry and fibre lay-up, and accurate data of GFRP fracture energy is largely unknown. When no actual post-failure behaviour is acquired, the lower bound fracture energy can be determined from the material properties. Numerical analysis of uni-directional coupon experiments is performed to determine the input values and response of the lower bound fracture energy. The lower bound fracture energy implementation results in an abrupt drop in stress when the material strength is reached. Increasing the lower bound fracture energy by a minimum of 2% prevented numerical inconsistencies. Progressive failure analysis of multi-directional coupon experiments validated an increase of 10% for the lower bound values. The use of lower bound fracture energy for non-linear buckling analysis is verified with progressive failure analysis of the buckling experiments. The lower bound fracture energy, increased by 10%, approximates the ultimate strength of six tests with an average difference of 7.7%. To analyse the non-linear buckling behaviour of a GFRP plate, a buckling curve is created by varying the plate thickness. The influence of geometric imperfections on a plate's buckling strength is studied by applying different initial imperfections. Two types of boundary conditions are used to analyse if they result in a different buckling curve. A difference in the buckling strength reduction factor of 0.1 is found. Initial imperfections reduce the buckling strength of the material, which is most apparent for plate slenderness around 1.0. An initial imperfection of B/125 resulted in a 40% strength reduction compared to the elastic buckling strength. The average difference in reduction factor between an initial imperfection of B/1000 and B/125 was 16%, with a maximum difference of 26%.

Interest in composites for application in Civil Engineering structures, has seen significant increase in recent years. From composite repairs on existing structures from concrete or structural steel, to composite decks in bridges or even structures made solely out of fibre reinforced composites, the structural industry is following the already existing trend in automotive and aerospace industry where composite solutions present a great potential that traces back to 1960’s. Within this framework the Wrapped Composite Joints project, under Dr. M. Pavlovic, attempts to bring the composites technology to jacket designs of offshore wind turbines and replace the traditional welding technology that is used for connecting the steel tubular members of the jacket frame. Higher stiffness, more sustainable and lightweight design due to reduced steel weight and most importantly higher fatigue resistance are just some of the benefits that the developing technology brings in the structure. Developing a new technology especially when a novel material solution is used, requires robust knowledge of the inherent material as well as bond properties. For this experimental testing series should take place along different structural levels. Goal of such experimental series is to investigate the capabilities of the material as well as the assembled components up to total failure.
In the current Additional graduation work a coupon testing series comprising of different standard test methods, part of the Wrapped Composite joints project is presented. Aim of this study is the establishment of fundamental material elastic as well as fracture properties for the composite layup used in the project. Outcomes of the experimental study will be used as input for the realistic representation of the material and the bonded interface through Finite Element Models(FEM) of several scales, from small specimens to large and full scale Joints.