This thesis investigates using Ultrasonic Pulse Velocity (UPV) to check for near-surface damage in concrete structures without causing any harm to the material. The research started by reviewing past studies on UPV methods, helping to compare results and evaluate how well different techniques worked. The main goal then became testing three specific UPV methods: Indirect Method 1, Indirect Method 2, and the Pulse-Echo Method. The damages are intended from the opposite surface as which is being tested, and the purpose was to see how well these methods could spot these near-surface damages and whether they were able to measure the thicknesses of these damages. The study also looked at how different water-cement (W/C) ratios impacted the strength of concrete, including the compressive and the flexural strength, and how these changes in the end had influence on the UPV measurements.
The research was done in two parts. First, the three UPV methods were tested on concrete samples with different W/C ratios to see whether the pre-intended damages could be found, and the thickness could be estimated. Then, additional mechanical tests, like the compressive and the flexural strength test, were used to check the overall strength and condition of the concrete.
The results showed that Indirect Methods 1 and 2 worked well for detecting surface-level damage, but they struggled to find and map deeper damage of the concrete. In comparison, the Pulse-Echo Method was more reliable, as it could better detect changes in depth and accurately measure the thickness of near-surface or inner damage. This was partly because the wave direction of the Pulse-Echo Method is perpendicular to the surface of the concrete sample, and therefore a better control over the wave direction is achieved. Although the Pulse-Echo method had some limitations, such as not being able to fully map the shape of the damage due to a lack of measurement points, it outperformed the other indirect methods in detecting and estimating the sizes of the pre-intended damages.
Another important finding was that concrete with a lower W/C ratio had more pores in this specific case, which seemed to be caused by issues with compaction and curing. These problems weakened the mechanical strength of the low W/C ratio concrete. Due to this finding, the study suggests that future studies should perform quality checks before testing starts, so this phenomenon could be prevented in future research. Other recommendations of this study include, upgrading UPV testing (especially for the indirect methods) with better sensors and signal processing, and exploring hybrid non-destructive testing methods. Furthermore, future research should also involve real-world testing to better understand how these methods perform in practical situations.
To sum up, while the Pulse-Echo Method was the best at detecting and measuring the intended damages, there is still room to improve the indirect methods by refining the tools and techniques. This would probably allow them to localize and determine the size of deeper damage in concrete structures.

In Europe, including the Netherlands, a significant Replacement and Renovation (R&R) challenge is expected between 2040 and 2060 for concrete bridges and viaducts due to ageing infrastructure reaching their end of service-life. Various options emerge when existing structures fail to meet current requirements, including accepting additional risk without mitigation measures, making minimal adjustments for a short period, or implementing longer-term modifications. Existing frameworks for assessing R&R decisions, include technical and cost aspects, although lack of sustainability criteria and performance prediction.

The research objective is to develop a decision-making framework for evaluating different strengthening methods versus replacement, considering factors such as (environmental) cost, service-life, structural performance prediction and reliability. The research includes a comparison method on different strengthening methods, external prestressing (EP), memory-steel (MS), carbon fibre reinforced polymer (CFRP) and ultra-high performance concrete (UHPC), versus total replacement. The study mainly focuses on shear deficiencies and strengthening for shear in precast pre-stressed T-beam bridges.

The research starts with a literature review on decision frameworks, structural deterioration mechanisms, T-beam assessment and strengthening methods. The literature review defines and elaborates on key performance indicators relevant to the study. The First Order Reliability Method (FORM) is used to determine failure probabilities by comparing demand versus capacity, providing insights into the current condition and expected lifespan of the structure. A multi-objective optimisation process is introduced to determine the most effective strengthening method based on the desired service-life extension. The goal of this optimisation process is to minimise (environmental) costs while maximising strength, subject to fabrication and physical constraints. A multi-criteria decision-making approach is applied, using the Analytical Hierarchy Process (AHP) to support complex decision-making where multiple variables and criteria must be prioritised. A parametric study is conducted to explore how (geometric) parameters influence decision outcomes.

The parametric framework enables the decision for optimal strengthening to be run multiple times, allowing trends and patterns to appear. Within the analysis, when accounting for varying spans, cross-sections, different states of current reliability and distinct deterioration phenomena for each strengthening method, CFRP consistently proves to be the best-performing and most frequently chosen option. This is due to its high strength-to-weight ratio, which helps minimise material costs and environmental impact. External prestressing excels mainly for larger spans and applying memory-steel is very unfavourable in any case when compared to other strengthening methods. Replacement ranks high in many cases but requires careful consideration, as the design is not fully optimised to each case and impact assessment remains less developed.

For complex geometries, the decision-making framework become less reliable, because strengthening and reliability calculations grow significantly more complex, which is not accounted for. A more integrated approach, considering the interaction between bending and shear, would improve the strengthening designs and could be further refined. Ultimately, while the framework provides a structured approach to decision-making, it should be seen rather as a supporting tool than a stand-alone decision-maker.

With the growing concern of aging infrastructures, the need for effective and non-intrusive monitoring techniques has become increasingly important. While most current methods rely on active testing, this study explores the potential of using ambient noise interferometry as a passive method for Structural Health Monitoring (SHM) of concrete structures. It investigates whether the Green's function (GF) of concrete medium can be adequately estimated from traffic noise to assess its health condition.

Two datasets are examined: a validation dataset from a laboratory experiment simulating ambient noise on a pre-stressed concrete girder, and real-world traffic noise data from the Maastunnel in Rotterdam. For each dataset, the following aspects are analyzed: (1) signal characteristics, including amplitudes and frequency distributions; (2) the optimal pre-processing scheme, incorporating temporal and spectral normalization, along with frequency filtering; and (3) the coherence of the resulting GF estimation from interferometry, particularly time of wave arrivals.

The results from the validation dataset demonstrate that ambient noise interferometry can reliably reconstruct the GF for concrete medium, indicating its effectiveness for monitoring changes such as crack formation and strain changes. However, the analysis of actual traffic noise data did not provide sufficient evidence to support its use for SHM with the current setup. Although a coherent and usable frequency range for traffic noise was identified, the limited amount of data led to a low signal-to-noise ratio (SNR), which made it challenging to highlight relevant features.

Moving forward, future researchers are encouraged to collect sufficient amount of data for analysis to better determine the feasibility of reconstructing the GF with ambient traffic noise. Additionally, exploring alternative sampling methods like continuous recording could address one of the limitations of this research. Finally, employing decomposition methods may help in increasing the SNR.

This thesis investigates the force transfer mechanisms between concrete substructures and steel pipe piles, specifically focusing on connections made using a concrete plug within the steel pipe pile. This thesis explores the mechanisms of force transfer in concrete plug connections within open-ended steel pipe piles, focusing on the viability of frictional (bond) transfer versus mechanical connections. The primary research objective was to determine the extent to which forces—both normal forces and bending moments—can be transferred through a concrete plug without the use of mechanical connections and to compare this with scenarios where mechanical connections, such as shear rings, are employed.

A comprehensive literature review revealed significant gaps in existing design codes and recommendations, which inadequately address concrete plug connections in steel pipe piles. Notably, regulations such as Rijkswaterstaat’s ROK V2.0 restrict the extent of force transfer through friction without clear justification. Existing standards like Eurocode 4 and the British Standard (BSI) offer bond strength values that vary widely and do not consider key parameters such as connection geometry and concrete shrinkage, potentially leading to inaccurate strength estimations. Although some models for grouted sleeve
connections might be applicable, their validation for concrete plug connections remains uncertain.

To address these gaps, a new analytical model was proposed to estimate the bond strength between
concrete and steel in plugged connections. The model incorporates factors including connection geometry, material properties, concrete shrinkage, surface irregularities, and the Coulomb friction coefficient. Push-out test results were used to update and validate the model, resulting in conservative bond strength values. Key parameters identified were the value for the surface and the Coulomb friction coefficient. The model’s predictions showed a Mean Average Error (MAE) of 0.589 MPa, primarily due to high variability in some test sets. However, the error was smaller for less variable data.

The findings indicate that connection geometry, particularly the diameter of the steel pipe pile, significantly affects bond strength. Smaller diameters exhibit higher bond strength due to better confinement and reduced concrete shrinkage effects. For larger diameter piles, where friction is insufficient to transfer normal forces, mechanical connections such as shear rings are recommended. These connections were evaluated using Eurocode 4 and CUR Recommendation 77 and found to provide substantially higher normal force resistance, enabling effective utilization of the geotechnical load-bearing capacity.

Regarding the transfer of bending moments, the study found that the wrenching mechanism between the concrete plug and steel pipe pile can manage the transfer through contact stresses. This stress distribution is linear along the plug height and sinusoidal around its circumference, provided it remains within allowable concrete compressive stress limits. The plug’s length should be designed to ensure these stresses do not exceed permissible values. A model for the interaction between bending moment and normal force was also developed, indicating that additional normal force resistance can be achieved under a certain bending moment, though this requires careful stress distribution verification.

In conclusion, while friction can achieve normal force transfer in concrete plug connections, it is often insufficient for larger piles. Mechanical connections such as shear rings offer a more effective solution, providing significantly higher normal force resistance and enabling efficient design. The wrenching mechanism can be used to transfer bending moments, but the ultimate bending moment resistance is governed by the concrete plug’s cross-sectional resistance. This is because the resistance of the concrete plug’s cross-section is lower than the wrenching resistance. This research provides a comprehensive framework for understanding and optimizing force transfer mechanisms in concrete plug connections within steel pipe piles, highlighting the importance of mechanical connections for effective and practical design.

To limit the need for clinker in cement, CEM III/B is being used more and more in infrastructure. This cement mixture uses significantly less clinker, but instead uses blast furnace slag. Since this is a waste product of the steel industry, CEM III is supposedly much more sustainable than CEM I. However, its mechanical properties are different as well. There has been plenty of research comparing the mechanical properties of CEM I and CEM III concretes, and CEM III concrete seems better in many ways. However, for these experiments only perfect curing conditions had been used. The conditions on the building site are often far from perfect, and affect the integrity of the concrete.

This research has compared the mechanical properties of CEM I 42.5N and CEM III/B 42.5N concrete mixtures in a relative humidity of 55%, which is a realistic value for the building site. This low humidity has a major effect on the hydration, which also affects all mechanical properties. With the help of an experimental campaign, these mechanical properties were tested.

To conclude the findings of this research, it can be stated that sub-optimal curing conditions affect CEM III significantly more than CEM I. Not only are the mechanical
properties lower, but there is a higher uncertainty in the CEM III mechanical properties as well. Applying CEM III in sub-optimal conditions would require extra careful
considerations in the treatment. In the given building site conditions, applying CEM I
would be significantly more durable, cheaper, and especially safer.

The use of non-destructive tests for assessing the material status of concrete structures in the Netherlands remains relatively uncommon, despite the growing demand for the preservation of existing structures under the VenR policy of Rijkswaterstaat. Skepticism towards NDTs is reflected in the scarcity of documented case studies in publicly available literature and in the absence of rules and guidelines.

In this research, following an extensive literature review on the current state of assessing the material status of reinforced concrete structures using NDTs, a large-scale non-destructive inspection was carried out on the Sluinerweg viaduct. The research aimed to address the practical challenges associated with these methods. These challenges serve to formulate a practical methodology to facilitate future inspections. Limitations include the use of specific NDTs: GPR, UPE, rebound hammer, UPV, half-cell potential, resistivity, and corrosion current density. Following the inspection, a data analysis was conducted, accompanied by a destructive verification of the methods.

The integration of GPR with UPE technology showed promise for tendon duct inspections. However, a 12 mm borehole used for destructive verification proved to be too small to make accurate judgments. Additionally, the absence of grouting defects made evaluation of the method challenging. GPR provided a more accurate estimation of the cover depth compared to previous measurements conducted on the Sluinerweg viaduct using a standard cover meter. However, it was impossible to measure through the cathodic protection coating. The data's correlation with the provided drawings is promising, especially given that drawings are often unavailable. The key finding regarding the estimation of compressive strength using the rebound hammer and UPV is the strong recommendation to avoid using SonReb models unless they are specifically calibrated for the structure under inspection. No active corrosion sites were found, which posed challenges to evaluating the methods. Resistivity values measured using the Proceq Resipod consistently showed lower readings than those obtained with the Gecor-10 Wenner probe. A laboratory investigation ruled out moisture content as the cause. Fortunately, the differences are less pronounced with corroded reinforcement; however, further investigation is necessary. The previous inspection regimes in the Liggerkoppen project were found to be suboptimal in some aspects but were deemed reasonable considering the complexity of the project.

This research demonstrated the effectiveness of several NDTs in-situ, which should help to build trust in the reliability of these methods for future inspections. Based on the findings of this research, it is strongly recommended to conduct further large-scale inspections to improve the practical methodology, gain further experience and develop improved codes and guidelines. While there is still much to accomplish, Rijkswaterstaat's support for investigations such as the one conducted for the Sluinerweg viaduct demonstrates their commitment to a better future.

Steel-concrete composite (SCC) slabs are extensively used in construction, particularly in multi-story buildings, due to their efficiency and structural performance. SCC slabs combine the strengths of steel and concrete, where steel provides tensile strength and concrete offers compressive resistance. This integration results in lightweight, robust structures that save costs and allow for taller buildings with larger spans.
New designs of steel-concrete composite slabs have to be extensively tested before the new designs are approved. It is therefore important that information is gathered during testing. Strain measurements are often done on composite slabs, for example, strain gauges have been applied to the steel sheeting and distributed optical fibers (DOFs) have been applied to the reinforcement rebars. However, there have never been distributed strain measurements on the steel sheeting of steel-concrete composite slabs. This research aims to gain new insights into the structural performance and behaviour of deep steel-concrete composite slabs using distributed strain measurements.
SCC slabs often have embossed regions of steel sheeting, these embossments or indentations transfer shear forces between the steel sheeting and the concrete. DOFs were applied on the embossed parts of the steel sheeting in the direction of the span in four composite slabs. The strain data showed oscillations in the strain values, and that the embossed/indented parts of the steel sheeting were in tension, while the flat areas were in compression. Local deformations, due to the geometry of the embossments, caused the oscillations.
The N.A. position was another critical focus of the study, which was determined using fiber data at five locations on the middle rib of three slabs. The N.A. was determined for three loading stages: initial, elastic, and plastic. The fibers captured the upward movement of the N.A. from the steel sheeting into the concrete during the initial and elastic stages, as expected according to theoretical calculations of the N.A. position. However, in the plastic stage, the N.A. shifted downward, back into the steel sheeting, instead of continuing its upward trajectory, as expected. This unexpected shift was attributed to partial shear interaction, where the steel sheeting and concrete began acting separately, leading to separate strain
profiles.
Buckling of the steel sheeting was observed in two slabs, Slabs 10 and 11, with fibers providing critical insights into the timing and extent of buckling. In Slab 11, where four fibers were located in the buckling zone, two fibers showed early signs of buckling in the top flange at 97% and 98.3% of the peak load. The strain patterns indicated buckling before the peak load was reached, offering valuable data on the onset of this failure mode. For Slab 10, buckling was detected after the peak load.
Lastly, the research explored the use of DOFs for crack detection. Fibers were applied to the bottom of the ribs on one slab to identify crack locations based on strain data. While cracks typically cause localized peaks in strain, the results revealed limitations in the accuracy of crack detection using DOFs on steel sheeting.
In conclusion, this research demonstrates the potential of DOFs for strain measurement in steel-concrete composite slabs, offering valuable insights into strain distribution, N.A. position, and buckling behaviour. However, the crack detection capability of DOFs, particularly when applied to steel sheeting, requires further refinement to improve accuracy and reliability.

In the construction industry, composite structures combining concrete and steel are commonly employed in floor systems due to their exceptional performance in compression and tension. With a growing emphasis on sustainability and Life Cycle Assessment (LCA), this thesis introduces a novel concept: a modularised floor system consisting of reusable concrete deck and composite beam. This research focuses on analysing the behaviour of an innovative demountable "concrete to concrete" by FEA. A connection between the composite beam and concrete deck connected by a shear connector (bolt). The goal is to understand the mechanical behaviour of such connections.
This design differs from cast-in-situ traditional composite floor systems by having a concrete deck divided into three separate parts that are connected by bolted shear connectors. The composite floor consists of composite girders and concrete decks. A key advantage of this system is the ability to extract the concrete deck from existing floor systems, offering economic benefits and reducing carbon emissions over its life cycle. The mechanical performance of the newly designed connection between two concrete segments (a composite beam and a concrete deck) is examined through a shear and bending model using Abaqus Software.
The shear model does not represent a real case loading, and it is introduced to gain confidence in the numerical analysis due to the absence of experimental data in this research. The specimen consists of two concrete blocks being pulled apart. These blocks are connected by a demountable shear connector (bolt) in the middle.
A three-point bending model presents the mechanical behaviour and realistic potential failure modes of the innovative demountable "concrete to concrete" connection. It consists of three connected concrete segments. This model reveals failure modes, including cracking at the “re-entrant corners” of the connection points, crushing of concrete at the mid-plane of the connection and under the bolt nut, and transverse concrete cracking originating from the bolt hole, refer to Figure 6.26.
To enhance the structural behavior of this modularised floor system, several methods are investigated. First, adding steel plates at the connections effectively mitigates concrete crushing at the mid-plane and prevents cracking at the re entrant corners. Second, relocating the connection to zero-bending moment positions results in a notable reduction in the three failure modes, improving loading capacity by about 10%. Furthermore, the environmental impact of this novel design is noteworthy. With the assumption given in this thesis, for an area of 5.67m*8m concrete deck, reusing the newly designed concrete deck can result in a savings of approximately 4.2 tonnes of CO2 emissions per subsequent life cycle. Similarly, reusing concrete decks from existing buildings can lead to a reduction of around 2.33 tonnes of CO2 emissions per life cycle with this size of the floor. Based on the assumptions made in this research, the results suggest that the newly designed concrete deck may have a lower loading capacity than traditional concrete slabs. However, its potential economic and environmental advantages make it a promising topic for future investigations.

This research investigates the integration of environmental costs into the cost-benefit analysis (CBA) framework for constructing circular viaducts. Circular viaducts offer environmental benefits but face challenges due to their higher initial construction costs. The traditional CBA framework focuses solely on economic costs, hindering the adoption of circular construction. This research proposes a methodology to monetize environmental costs and integrate them into the CBA framework to make informed decisions about circular viaduct construction.
The methodology involves analysing the environmental impact of circular viaducts and traditional viaducts using Life Cycle Assessment (LCA) and Environmental Product Declarations (EPDs). The environmental impact is then monetized using agreed-upon values from various stakeholders. The monetized environmental costs are incorporated into the CBA framework using cash flows and the net present value (NPV) method.
The research findings indicate that the implementation of circular viaducts is most viable in scenarios with longer lifespans. In these scenarios, the overall environmental costs of the circular viaduct are lower than those of the traditional viaduct due to the lower frequency of replacement. However, the NPV analysis reveals that the traditional viaduct has lower present value environmental costs in all three scenarios. This is due to the difficulty of accurately predicting future material prices, which could significantly impact the economic benefits of material reuse in the circular viaduct.
Results show that while the circular viaduct exhibits higher environmental costs in some scenarios, its economic benefits through material reuse, particularly in scenarios two and three, make it a more viable option. However, further research and development are needed to reduce the initial environmental and economic costs of circular viaducts to achieve a wider and faster adoption of this sustainable construction method.

Bent up bars were prescribed as shear reinforcement in the first half of the twentieth century, stirrups after the 1960’s. In current Eurocode, bent up bars can be applied again, but restrictions with respect to the maximum shear strength should be followed. Goal of this report is to provide background for this shear strength restriction and provide an assessment method for concrete structures reinforced with bent up bars.

First part of the report analyses critical design aspects of bent up bars in the transfer of shear stresses with help of truss models. Second part explores the shear strengths of reinforcement sections and concrete struts with help of outcomes of experiments performed in the past. In last part, the obtained insights are collected and captured into a conceptual model. This model is employed to describe the expected failure mechanism of bent up bars and reflect on assessment methods and maximum shear strengths of specimen reinforced with bent up bars.

Consequence of the application of bent up bars in concrete structures is the formation of cracks in the supporting concrete strut by curved sections of bent up bars. The remaining shear strength of concrete structures depends on the shear resistance of cracked concrete struts.

The findings in this report implies that any model based on the tensile strength of inclined members is applicable for the analysis of bent up bars as long as the applied shear stresses are limited to ten percent of the compressive strength. Also, the application and assessment of bent up bars in concrete structures requires special attention to: shear and flexural reinforcement inclusive designs, cover spalling mechanisms, and detailing of anchorage regions flexural reinforcement bars.

Amid global climate change challenges, the construction industry faces an urgent  transition from a linear production model to a Circular Economy (CE). Initiatives  and recommendations in Dutch transition roadmaps and literature predominantly  focus on ensuring a future circular built environment, while lacking concrete actions on leveraging the existing assets for reuse. Dutch CE roadmap timelines  and interventions are developed based on Material Flow Analysis (MFA) studies with highly uncertain data input, this uncertainty impacts either environment or  economy with inaccurate interventions on the CE-transition. Secondly, the Replacement & Renovation (R&R) task of civil structures poses a threat for the  industry due to the limitations of capital, contractor capacity, and material  resources required to facilitate this peak. There is currently a lack of centrally  stored high-quality physical asset data available at public organisations. This data is essential in effectively managing the decommissioning peak and reduces risk for reuse realization. Lastly, Asset Management (AM) is transitioning towards a 3D-centralised strategy in line with Building Information Modelling (BIM) and  digital twins, while existing assets are still in 2D with often incomplete and  fragmented data documentation. Consequently, a large data quality gap is forming between new and existing assets. This led to the research question: How can centrally stored, quantified, and visualised asset data of existing infrastructure impact the CE-transition, bridge R&R-task efficiency, and AM practices? An upgrade towards 3D-BIM is required for existing assets to bridge this data gap. In doing so, facilitate higher quality- and more accessible asset specific  information that can be used in reusability scanning and structural assessments,  material quantification for CE-transition roadmap accuracy, and numerous AM  benefits. The costs for upgrading the existing assets using manual modelling or  3D scanning technology are currently too large to justify. An opportunity was  identified for modelling 3D-BIM of existing beam & slab bridges from 2D drawings using a modular approach to Parametric Engineering, aiming to reduce the investment threshold, and accelerating the digitization transition. Preliminary testing executed by the author showed a potential for 50-80% reduction in modelling efforts compared to conventional modelling practices with a volume  accuracy of >97%. The prototype calls for further development, validation, and similar efforts for other infrastructure types. The tool also showed potential for 3D structural & reusability assessments, reinforcement approx., and ptioneering & circularity scoring for the design phase. To put the tool’s use in perspective, a roadmap towards 3D centralized AM and a reuse economy was developed for AM.

A significant part of composite concrete viaducts was built in the 50s and 60s. This has led to an increasing need for the reassessment of the precast concrete beam bridges in the Netherlands. Many of those bridges are nowadays subjected to higher traffic loads and consequently, have a certain risk of not complying with the currently used design codes. As a result, there is a demand for the development of nonlinear finite element solution strategies, which would increase the reliability of the numerical methods in safety assessment. In this research, special consideration is given to the precast, prestressed beam bridges which were made continuous by applying cast-in-situ cross beams and a top layer above the supports. In such structures, the hogging bending moment introduces more complex stress conditions in the concrete parts and more specific at the interface between precast girders and the top slab, compared to simply supported beam bridges.
Thus, one of the key aspects of the structural performance of composite bridges is the interfacial behaviour. The focus of this research is to study the stress conditions in the vicinity and at the interface and explore methods of numerical modelling of the interface in concrete-to-concrete connections between precast beams and top layers to initiate the development of modelling strategies for this type of interfaces.
The literature review was focused on prefabricated beam bridges, the current state of knowledge on concrete-to-concrete interfaces, along with design recommendations and past experimental and numerical research. Moreover, available interface element types, material models and modelling guidelines were explored. Since DIANA FEA is used within the course of this research, the study of the available models was limited to the ones provided by this software. It was noted that the Linear Elasticity model is the simplest way of interface modelling, therefore it was utilised in the initial stage of the research. More advanced models, Coulomb Friction and Combined Cracking-Shearing-Crushing, were considered worth investigating owing to accounting for coupling between normal and tangential behaviour. The Nonlinear Elasticity material model was also recognized due to the introduction of nonlinear effects, yet being relatively simple to assemble.
The initial phase of the research was a linear, phased analysis of the continuous, composite, concrete girder. Three models were tested within this part of the research – the model without interface elements, and two with linear elastic interface elements, one having high, penalty stiffness and the other having lower, more realistic value of shear stiffness. It was verified that the models without and with penalty stiffness interface performed almost equally. The decrease in stiffness and the deterioration of the composite action caused by this, resulted in an increase of stresses in the precast element. By the support, the extreme tension raised by a factor of 1.21 and under the point of load application the compressive stresses in the beams’ web elevated by 2.26. Based on the linear analysis, no significant tensile stresses perpendicular to the interface were detected. According to the analysis of interfacial stresses interaction and assumed failure envelopes, at four chosen points - above the support, at midspan of the main span, at the local shear extreme and under the point of load application - it was observed that the point above the support is not at risk of failure, whereas the point in the midspan might be. It was concluded that the combination of stresses is relevant not only because of a possible decrease in capacity due to tension but also increase under compression. As a result, models accounting for coupling between normal and shear tractions and relative displacements are worth investigating. It was also observed, that cracking in concrete elements by the support is expected, hence nonlinear analysis is required.
The component-level experiments found in the literature were analysed in the following section to be able to perform verification study of Coulomb Friction (CF) and Combined Cracking-Shearing-Crushing (CCSC) interface material models. Based on single element FE tests it was concluded that both material models proved to be well-suited for capturing the shear-normal stresses coupling. With the same input parameters, but higher normal pressure, the shear capacity increased, representing well the reference data. The CCSC interface material model’s ability to capture both cohesion and friction softening, was also verified with the single element models. Moreover, tension softening based on mode I fracture energy can be accounted for in that material model, as well as the fracture energy’s and dilatancy’s dependency on confining stress. However, those parameters were not verified, due to, among others, limited experimental data. Element assembly with the CCSC material model for the interface, circular beam bond-slip reinforcement and nonlinear material properties of concrete, was used to analyse the specimens with rebars crossing the interface. This approach, was assumed to represent the force transfer mechanisms to the highest extent, since cohesion and friction, generated by both external pressure and reinforcing bars, along with their softening, as well as dowel action, can theoretically be represented by such model. It was observed that this type of strategy resulted in convergence issues, and due to large number of input parameters it is quite complex to analyse or further calibrate. However, the approach seemed promising since the peak loads were underestimated by only 7-15% with respect to the mean, experimentally obtained values.
In the final Chapter the Combined Cracking-Shearing-Crushing (CCSC) interface material model, with bond-slip beam reinforcements was applied in the nonlinear analysis of the previously analysed composite girder. As an alternative, the model with the Nonlinear Elasticity(NE) interface material model was also constructed, based on the analogous input parameters, to be able to compare the modelling methods. In total four models were analysed, since two sets of input, one based on Eurocode 2 and the other on best guess stemming from literature findings, were studied. What was found to be promising is that the global behaviour, assessed on the basis of crack patterns, of the beams with corresponding input, was quite similar for the analyses with the CCSC and the NE material models. With the applied numerical setup, it was not possible to obtain the total load-displacement path of the composite beams using the CCSC material model for the interface, since the models diverged. The NE material model performed more stable and allowed for the analyses to continue, which is its main advantage. Another benefit is the ease of assembly, in comparison with the CCSC model. Nevertheless, it was demonstrated that the NE might provide overestimated results due to not considering the interaction of tractions. It was highlighted that the models’ validation with experiments is needed to recommend one of the models or either of the input sets. It was recommended to simplify the approach with the CCSC material model, by for instance, simplifying the numerical setup of interface reinforcement. Moreover, according to the literature findings the scatter of cohesion and friction coefficients, as well as other input parameters, is still quite large, thus experimental research in the form of push-off tests focused on those, particular interfaces is recommended.

Nowadays, Rijkswaterstaat reassesses many older concrete bridges to guarantee their structural safety under the influence of increased traffic loads and stricter standards. Many of these concrete bridges contain open straight-legged stirrups, which are not allowed to take into account for the calculations of the shear resistance according to current standards. This often results in theoretical insufficient shear capacity and critical damage to structures, but this is not observed in reality. This indicates that the open straight-legged stirrups probably do contribute to the shear resistance, where an accurate assessment of this contribution could prevent unnecessary and costly structural safety measures. However, very few shear tests with relevant cross-sectional dimensions are performed and documented in literature, especially tests containing open straight-legged stirrups.

The application of Nonlinear Finite Element Analysis (NLFEA) is a useful tool to evaluate and understand the behaviour of structures, but provisions for the implementation of open straight-legged stirrups in concrete structures are lacking. Thus, the goal of this research is to provide a finite element modelling strategy that is able to accurately describe the behaviour of concrete beams with open straight-legged stirrups subjected to shear. The research focusses on describing the behaviour of rectangular concrete beams with open and closed straight-legged stirrups with finite element models using DIANA 10.5 [1].

Schramm [2] has performed multiple shear tests on prestressed concrete beams with several no longer permitted stirrups, including open straight-legged stirrups. He found that open straight-legged stirrups can significantly contribute to the transfer of shear forces [2]. The relevance of the rectangular test beams for comparison with box-girders is validated in this thesis, where the stress distributions in a linear elastic rectangular and box-girder cross-section due to axial forces, bending moments, shear forces and torsion are compared.

In the interest of providing a suitable solution strategy, Schramm’s test beams with closed and open straight-legged stirrups are reproduced with 3-dimensional nonlinear finite element models based on the recommendations of the RTD1016-1 [3], where the influence of various modelling considerations is investigated. The concrete is modelled with a smeared total strain-based crack model with the Hordijk tensioning and parabolic compression relations, including confinement and lateral cracking effects. Reinforcements are modelled as embedded truss elements with the Von-Mises plasticity model. To describe the accurate anchorage behaviour of the open straight-legged stirrups, the interaction between the surrounding concrete and the stirrups is described with the Shima bond-slip relation. The finite element model is first calibrated with a beam with closed stirrups, where modelling clamped restraints with supports on both sides of the beam result in a too-stiff response. By allowing a little rotational freedom in the form of boundary springs, the stiffness of the beam is manipulated without changing the overall load-bearing behaviour...

Concrete half-joints are a specific support detail in reinforced concrete structures, which reduce the construction height of the total structure. The use of concrete half-joints became popular around 1950s, but decreased its interest as a result of new insights on structural behaviour and collapses of these structures. Typical issues regarding concrete half-joints are either due to inadequate reinforcement detailing or due to deterioration mechanisms. The most critical deterioration is when a crack at the re-entrant corner allows for water ingress and thus corrosion of the rebars. This thesis focuses on the negative influence of this corrosion on the load bearing capacity and proposes an assessment method, which includes the reinforcement detailing. Firstly, problematic half-joints have been categorised and studied for reinforcement detailing. Subsequently, they have been analysed using an analytical tool, in which corrosion was implemented on the rebars. The outcomes were validated numerically.

For this thesis research, a series of Dutch concrete bridges has been studied to identify general reinforcement issues and categorise concrete half-joints. It has been observed that the majority showed short transfer- and/or anchorage lengths of the rebars and that all of them showed no shear stirrups as hanger-reinforcement. In stead, only a horizontal- and hanger rebar are present, which can be accompanied with a diagonal rebar, prestressing at the top or nib (or combinations in between).

An analytical tool is designed to calculate the load bearing capacity of (un)corroded concrete half-joints. The analysis is based on a lower-bound approximation using a strut-and-tie approach and an upper-bound approximation using a kinematic approach. The analytical tool is used to determine the load bearing capacity of the series of investigated Dutch concrete half-joints. Both approximations are comparable when rebar failure is the governing failure mechanism. The strut-and-tie approach also incorporates detailing checks, which are not considered in the kinematic approach. Therefore large differences occur when detailing governs the capacity.

The nodes in the strut-and-tie model, in which two ties are connected to one concrete strut, appear to be critical in the lower-bound solutions. The capacity depends on the concrete strength and dimensions of the node. The dimensions are influenced by the mandrel diameter of the hanger-rebar and anchorage length of the horizontal rebar. In order to study the influence of corrosion on the load bearing capacity, the effect of a reduced rebar capacity due to an increasing corrosion rate was implemented in the analytical tool. The kinematic approach appears to be more sensitive to load bearing capacity loss, as this calculation depends mainly on the strength of the rebars. The strut-and-tie approach is able to redistribute forces over the struts and ties and is less sensitive.

In order to verify the analytical results, a numerical study is performed. The specimens are modelled in such a way that rupture of one of the rebars at the re-entrant corner is governing. Both analytical solutions appear to be conservative compared to the numerical results, in which the lower-bound solutions are very conservative. Different crack’s angles have been found between the upper-bound calculation and numerical results. If the same angle is applied in the analytical tool, the difference reduces from 7% to 2% for an uncorroded concrete half-joint without diagonal. The differences can be explained by the simplification in the kinematic approach, in which the concrete compression zone is not able to transfer shear stresses.

Based on the conclusions of the analytical tool and numerical verification, an assessment method is proposed in which the upper-bound solution is combined with the lower-bound solution. If the load on the concrete half-joint is lower than the calculated lower-bound solution, the concrete half-joint is safe. However, questions arise if the load is between the lower- and upper-bound solution, in which structural safety cannot be guaranteed. The analytical tool is still a useful tool to understand the behaviour and vulnerabilities of the concrete half-joint. The analytical tool is even more useful if the strut-and-tie approach is governed by rupture of the horizontal-, diagonal- or hanger-rebar. The kinematic approach can be extended by implementing the same crack’s angle, which occurs in the existing concrete half-joint.

The Netherlands is currently facing a significant challenge regarding its highway system due to the rise in traffic, especially in densely populated areas like The Randstad. However, constructing new infrastructure or replacing old bridges is not a practical solution due to environmental concerns. Most of the country's prestressed concrete bridges were built in the 1960s and 1970s with a lifespan of 100 years, and they are deemed incapable of handling the current traffic volume. As the existing bridges are still in good condition, recent projects have focused on widening them. Widening a bridge involves careful consideration of the behavior of all the elements in relation to each other, given the existing deck's relative stability and the inevitable shrinkage and creep of new components. To ensure a monolithic connection between the new and existing sections of the bridge, current projects aim to widen the bridges using a closure pour between the main slabs.

The Schipholbrug, situated close to the Schiphol Airport, is a prime example of a prestressed bridge that needs to be widened, and it is the focus of this thesis. In the Netherlands, reinforced concrete is the preferred material for a closure pour due to its durability, cost-effectiveness, and established properties. However, to maintain the integration between new and old concrete, a 6-9 month delay after constructing the new bridge is necessary to build this closure pour. To minimize significant delays, it is crucial to maintain a strong connection between the original and new materials, including the closure pour. The main challenge is managing the differences in creep and shrinkage between the existing structures, fresh deck, and closure pour. These inconsistencies can cause significant tensile stresses in the closure pour, especially when delays are kept to a minimum. Therefore, identifying a cementitious material that could effortlessly create reliable bonds with the primary decks' prestressed concrete and possess a high tensile strain range property was necessary to reduce this delay.

Strain-Hardening Cementitious Composite, also known as SHCC, is a modern material that possesses an impressive tensile strain range and a comparatively lower elastic modulus. Nevertheless, what sets it apart is its strain-hardening quality, which improves its toughness even after experiencing cracks. This exceptional characteristic of SHCC allows it to offer an extended tensile strain range, making it a choice for a closure pour.

The thorough literature review investigated crucial subjects, such as the intricacies of closure pour when expanding current bridges. Moreover, it covered the fundamental attributes of concrete that are pertinent to this thesis, such as shrinkage and creep, as well as its post-crack behavior. Another segment focused on the primary material employed in this thesis, SHCC, emphasizing its fundamental characteristics, including shrinkage and crack. Lastly, the research included a section on imposed deformation that was custom-made to the specific case of this thesis.

The methodology chapter utilized analytical calculations to gain a better understanding of the deformation issues caused by shrinkage and creep and their effect on the closure pour. These calculations explored composite structure mechanics and imposed deformation to determine the longitudinal stresses present in the mid-span of the decks. To further verify the accuracy of the findings, a linear model was also developed using DIANA FEA...

To reduce the construction industry’s negative influence on global climate, emissions related to concrete consumption need to be addressed. This implies reducing the amount concrete used, by creating material-efficient structures. One of concrete’s main advantages is that it can be moulded into virtually any shape. Despite the fact that modern digital design tools enable the effortless design and calculation of lightweight and graceful structures, this potential often goes unrealised. This can be attributed to the challenges associated with constructing intricate and custom geometries using conventional formwork techniques that depend on single-use cut timber or milled foam. Not only do these methods make the construction of these types of structures labour and cost intensive, they also cause them to be wasteful.

KnitCrete, which uses knitted technical textiles as stay-in-place moulds for concrete structures, has proven to be a solution for building doubly curved structures, eliminating the need for time-consuming, costly, and wasteful moulds. However, due to its inherent high flexibility and the challenges of predicting and controlling the geometry during the casting process, the technology relies on coating procedures using high-strength cement paste coating to stiffen the geometry before concrete can be poured.

This research addresses both issues and proposes a design approach, which models the deformation behaviour of the uncoated knitted formwork under concrete pressure to determine the final geometry of flexibly formed concrete structures, hence gaining better understanding on the deformation behaviour of knitted textile formworks and bypassing the stiffening steps during fabrication.

Developing a method to predict the final geometry of flexibly formed concrete structures involves various research disciplines, including material science, and structural mechanics. The research approach is divided into three parts. The first part investigates the stress-strain relationship of various textiles with different knitting patterns, alongside the rheological and mechanical strength properties of different cementitious mixtures. The second stage focuses on developing (semi-)analytical models to predict the deflection behaviour of membranes subjected to varying boundaries, loads, and material properties. Finally, the accuracy of the models are validated by the construction of multiple prototypes.

In conclusion, this thesis introduces a fabrication system that exploits the deflection behaviour of flexible formworks to create funicular shell structures and lays the foundation for implementing (semi-)analytical approaches to model these deformations.

On a general level, the Dutch government wants to have a fully circular economy by 2050 by reducing the use of primary materials and carbon dioxide emissions. As the consideration and integration of concepts such as sustainability and circular economy are becoming increasingly popular in the civil engineering sector, it might be time to re-consider certain activities.

From both scientific and practical points of view, it is concluded that currently a great deal of research is focused on stimulating concepts such as sustainability and circular economy in the “early stages” of the lifecycle such as procurement, design, and construction stages. However, the aforementioned concepts are not yet elaborately researched in stages after construction, such as the maintenance stage. However, in the Dutch context, there are hundreds of existing civil engineering assets, that need to be maintained daily. As the Dutch government has certain goals, it is important to see how maintenance strategies for existing civil engineering assets can be affected in the case when sustainability and circular economy are considered.

This research aims to explore the integration of concepts such as sustainability and circular economy within the maintenance stage of existing civil engineering assets. As a result of this research, a tool is developed in Microsoft Excel. This tool referred to as “Maintaining sustainably and circularly in a collaborative way” can be used by actors involved in the maintenance stage. It is possible to apply the tool in the following two phases, namely (1) the pre-contractual phase and (2) the execution phase for maintenance works. With the help of indicators, the actors involved can (re)consider aspects such as the (current) maintenance strategies, and the requirements for maintenance contracts. The tool can help to overcome certain identified barriers such as knowledge gaps on sustainability and circular economy within the maintenance stage, and diffused collaboration among parties involved in a certain process.
For this research, two important constraints to mention are:
(a) The developed tool is currently only applicable for sluices and bascule bridges (in Dutch: beweegbare bruggen), and
(b) the focus of this research is solely on performance-based contracts for maintenance works.

As an approach to conducting the research, the “Double Diamond Methodology” is applied. This is a design-thinking research approach. In the first part of the diamond, literature is reviewed and semi-structured interviews are conducted. The results of the literature review and the interviews led to the requirements that should be used as a basis for developing the tool. In the second part of the diamond, the tool was developed and tested via validation sessions.

We are currently facing a transition of economy. Previous years were focused on a linear economy, consisting of the make-waste concept. The products that are made with raw materials are thrown away after its use. Unfortunately the Earth does not contain an unlimited source of materials and we need to focus on reusing materials. Concluding to create a circular economy in which waste does not exist at all.

The goal is to start with reusing as of today, instead of in the future. In other words, using the current existing elements. However, to do so it must be known which elements are available. Therefore, a data analysis has been done on the current existing structures as well as the future perspective. These analyses combined concluded in a common scope, visualized as a Lego box. This Lego box does not only consist of all the current existing structures (within the determined scope), but also provides a future perspective on the demolishing plans in the near future. Based on a time-consuming manual research a variety of nearly 70 viaducts have been examined. This lead to the summarization of 5 different girder categories: Box girders, inverted T-girders, Infilled girders, T-girders and remaining.

With the specific girders known, design applications can be created. The focus on these applications is to think outside the box and reusing a girder in a different function than the original purpose. The design applications are created with a brainstorm session. For this session multiple different broad-minded individuals had been invited for an open discussion which concluded in over 20 different design applications. Thereafter, these applications have been examined with the help of an MCDA, based on the three main criteria. This MCDA is executed with the help of multiple different experts with a background regarding one of the three main criteria. With these expert judgements the total amount of design applications have been demarcated to a top 5. Reusing a girder as: Bicycle bridges, (non-)residential buildings, retaining walls, sound barriers and culverts

In conclusion, this thesis provides valuable outputs and the first impressions regarding reuse in another application seem at least interesting. With the different impact factors determined, the possibility looks very promising. It can be stated that reusing in general will be better for the environment, as well as for your own wallet. Reusing a girder as culvert can in theory be seen as a good reuse application, but not higher in a general value than reusing again as a girder. This is based due to the fact that using the girder as a culvert will take more research in practice, especially regarding structural aspects. However, from this thesis it the first impression conclude in the fact that the impact in costs as well as environmental impacts are bigger when reusing the girder in another function

The dolmens erected in the province of Drenthe between 3350-2700 BC are the most ancient monuments of the Netherlands. They consist of a long assemblage of rocks capped with boulders which served as burial chambers for the Funnel Beaker population. Despite their robust look, dolmens are vulnerable. For example, one of the caprocks of dolmen D14 fell off in 2019, once again. The method currently used to repair megaliths is not optimal: a crane is mobilized and the rocks are repositioned using a trial and error strategy. The reconstruction scenario should be selected and fine-tuned digitally beforehand. Moreover, the structural stability of the new assemblage of rocks should also be checked numerically. This necessitates a digital model of all the rocks that have to be rearranged. Not only the visible part of these rocks has to be digitized. The buried parts of the support rocks have to be modelled too as these rocks might have to be displaced and tilted to obtain a more compact and interlocked structure. Since dolmens occupy a prominent position in the Dutch heritage, only non-destructive see-through techniques have to be used for imaging the hidden contours of the bearing rocks. In addition, the bearing stones have complex geometries and are not isolated, which increases the complexity of the problem.

Two suitable geophysical methods are the Ground Penetrating Radar (GPR) and seismic techniques with a focus on reflection measurements. For the GPR specifically, we choose a Common Offset Survey, which can map reflections from the subsurface. For the seismic techniques, we choose a line array measurement, among others. We use the GPR to estimate the buried rock contour of the keystone Sl2 of megalith D14, which is a bearing stone formerly supporting capstone D9. We perform several reflection tests on various rocks unrelated to D14 using different seismic sources and receivers to estimate the reflection depths. We follow a proposed approach for both methods.

To evaluate the GPR data from the field, we assume a simplified GPR with zero-dimensional antennas (GPR point model). Subsequently, we develop two mathematical models (GPR point-to-GEO and GEO-to-GPR point model), based on this conceptual model in order to I) calculate the (buried) rock surfaces from field data and II) model field data from estimated buried rock contours.

We first perform the Common Offset Survey on a non-buried boulder on the campus of the TU Delft to evaluate the accuracy of the developed GPR point-to-GEO model and to optimise the second survey on keystone Sl2. We first perform the seismic reflection measurements on several rock samples to determine the best seismic source. Finally, we perform a line array measurement on a cylindrical basalt column using 300 kHz transducers.

We calculate rock contour coordinates from the GPR data and these show a reasonable fit with the contour of the TU Delft boulder, with an accuracy of 5-10 cm. For the keystone Sl2, the maximum burial depth is determined to be 80 cm at the southern side. The bottom of the keystone is sloping downward starting from ground level at the northern side. The southern, eastern and western rock faces are steep, almost vertical, which is confirmed by historic photographs. However, the calculated (buried) rock surface coordinates consist of an incoherent set of coordinates with locally a lack of data or blind-spots. Estimating a coherent buried rock contour, therefore, requires shortcuts and a decrease of accuracy is to be expected especially for rock surfaces near blind-spots in the GPR data. Furthermore, the identification of relevant reflection surfaces is rather subjective and combined with blind spots in the acquired GPR data, this can lead to wrongful interpretations of the buried rock contour.

The seismic reflection measurements we perform give clear reflections for the 300 kHz transducers on rocks of limited size with simple geometries. However, the transducers should first be applied on rocks with increasingly more complex geometries before being applied in the field. The accuracy in the order of 1 cm can be considered promising, but its applicability for complex geometries and reflection depths larger than 0.5 m remains unknown.

The main motivation for this research originated from two ambitions, which involve many challenges for which circular solutions have to be developed. First, the ambition of the Dutch government to achieve a circular economy, which also includes a circular construction industry, in the Netherlands by 2050 at the latest. Secondly, in line with the first, the ambition of Rijkswaterstaat to work climate-neutral and circular in 2030. At this moment, the main focus in the Dutch construction industry is on developing circular solutions which can be implemented and applied during the enormous replacement and renovation task of many of the almost 40.000 bridges and (mostly) viaducts in the Netherlands. Therefore, the main focus of this research has been on developing circular solutions for concrete viaducts for (governmental) roads. This has resulted in the development of a concept demountable footing to foundation (F2F) dowel connection which has been based on, and is suitable for application in, the proposed design of a standard (circular concrete) viaduct. Besides, attention has been paid to desired monitoring aspects regarding such a circular viaduct, and to the life-cycle costs of a circular viaduct compared to those of the same viaduct, constructed in a traditional way, characterized by a linear life-cycle model.