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...

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.

Uncertainties regarding structural safety of reinforced concrete structures may warrant a need for a detailed assessment. A detailed assessment using nonlinear finite element analysis is one of the alternatives which could help in decision-making about maintaining, upgrading or even demolishing and rebuilding of the structure. A reliable assessment should account for the existing damage in the structure, which may cause re-distribution of stresses within the structure, giving rise to unexpected failure modes. The existing approaches in nonlinear finite element analysis which account for the effect of already undergone damage in concrete, pose a number of limitations which either makes structural analysis ambitious or the uncertainty of concrete damage is not effectively accounted for. An alternative approach is adopted in this thesis, which is phenomenological and probabilistic in nature. Existing damage in concrete is conceived as a statistical field, which can be input into a finite element model, such that the existence of damage is taken as the starting point of the structural analysis. Focusing on indications of damage on the surface of concrete, i.e. crack patterns, an exploratory methodology based on image analysis is developed, to account for information obtained from crack pattern observation into nonlinear finite element analysis of reinforced concrete structures. The methodology is implemented on MATLAB and validated on damaged experimental specimens. Results of the computational analyses indicate good efficiency in predicting residual load carrying capacities and failure modes, alongside insightful numerical crack patterns. Through a critical examination of the obtained results and reflection upon the assumptions and simplification made in the methodology, recommendations for future research are provided.

The innovative shear strengthening method using externally bonded CFRP reinforcement to strengthen prestressed concrete I-girders has been investigated in this thesis. These girders potentially have insufficient shear capacity because of the combination of thin webs and insufficient shear reinforcement. Shear failure of these girders should be prevented because they do not warn before the element fails in shear. Shear strengthening using externally bonded CFRP reinforcement seems promising because of low installation costs, negligible increase in weight, no decrease of clear height underneath the bridge and minimising the hinderance. The aim of this thesis is to investigate the feasibility of shear strengthening prestressed concrete I-girders using externally bonded CFRP reinforcement. The shear behaviour of prestressed concrete I-girders strengthened using externally bonded CFRP reinforcement has been investigated with the nonlinear finite element analysis (NLFEA) software DIANA. A three-dimensional finite element model of a 1.0 m high prestressed concrete I-girder with a kinked tendon profile and no shear reinforcement has been made to investigate several parameters and aspects of the CFRP reinforcement. Shear strengthening of prestressed concrete I-girders with vertical CFRP sheets and CFRP anchors is a feasible strengthening method because of the demonstrated potential increase in shear capacity. The externally bonded CFRP reinforcement was especially effective to increase the flexural shear capacity of prestressed concrete I-girders. The numerical analysis showed a promising increase in flexural shear capacity between 40-55% and an increase in ductility of more than 80% compared to the I-girder without CFRP reinforcement

The stay cables of the north bridge of the Galecopperbrug are reaching the end of their life span. Rijkswaterstaat, which is responsible for the bridges, needs a reliable Structural Health Monitoring (SHM) method to monitor the current state of the stay cables. At the moment, Rijkswaterstaat experiences issues with defining the state and the residual life span of the stay cables of the Galecopperbrug. This study focuses on the technique of Acoustic Emission (AE) for monitoring the stay cables of the Galecopperbrug. The main research question of this study was: “Is the AE-system used in a fracture-based assessment suitable for structural health monitoring of the stay cables of the Galecopperbrug?”. In this study the following methods were used to investigate the AE behaviour of stay cables: a literature study on previous research and the current knowledge of AE and the structural behaviour of cables was done, a full-scale and two verification experiments were performed to investigate the AE behaviour related to wire breaks and to investigate the accuracy of linear source location techniques, an analytical model of the stay cables was made to investigate the influence of different parameters to the capacity of the stay cables and to predict the stress distribution in the wires during the experiment and finally, a SCIA model of the Galecopperbrug was used to investigate the load bearing distribution of the Galecopperbrug. In this study, it was found that wire breaks inside (stay) cables will generate elastic stress waves which can be captured and recorded by AE sensors. Based on an experiment where multiple wire breaks occurred, it was shown that wire breaks can be identified with the help of AE techniques. However, the identification of wire breaks is mainly depending on the correct choice of sensor type. Based on the experiments and assumptions that were made in this study the R6I-AST type of sensors are more suitable for wire break detection and the R3I-AST sensors are more suitable for AE signals due to impacts. Based on the assumptions and the experiments performed in this study it can be concluded that AE can be used in a fracture-based assessment for SHM of the stay cables of the Galecopperbrug.

Recent major tsunami events generated by earthquakes inundated coastal cities and caused extreme destruction and loss of human lives. The collapse of coastal bridges due to tsunami wave impact represents a huge obstacle for rescue works. The need to understand tsunami effects and develop tsunami-resilient bridges became apparent in the aftermath of extreme tsunami events in the Indian Ocean (2004), Chile (2010) and Japan (2011). Different coastal topographies affect tsunami propagation near shore. Varying wave characteristics lead to various failure mechanisms of bridge decks. Together with the wave characteristics, the bridge properties and the settings around the bridge play a major role in this failure, think for example of shear keys, seawalls or inclination of the bridge. To find out more about these failure mechanism and what role all these measures have in the failure, a laboratory experiment is executed and a numerical SPH model is set up to investigate the impacts of various wave characteristics, a seawall, shear key and inclination of the bridge deck. The numerical SPH model is validated with the help of wave gauge data and tracked bridge deck movement from the executed physical tests. In this thesis the focus is on the movement of the bridge deck, what kind of effect do the different interventions have on the movement of the deck. Since the movement is highly dependent on the forcing on the bridge deck, the forces are analyzed thoroughly. From the force time series countermeasures are proposed and modeled in the SPH model. Wave forces from different type of waves are simulated with the SPH model. The overall behavior of the hydrodynamics and the deck movement are validated and suited for qualitative analysis. Some disadvantages of the model are the lack of bottom friction and air bubbles in turbulent regions. The 3D model represented the movement on the deck in a very good way, runtimes and storage capacity formed an obstacle. A 2D model was used to do qualitative analysis of the changes of wave characteristics and the effects of the structural measures. The limiting factor in the commercial use of SPH is the computation time. In future models this could be accelerated by the use of GPU processors instead of CPU processors which are able to solve many parallel processes at the same time. Apart from wave heights and inundation heights, the wave phase appeared to be a major decisive factor in the failure method of the bridge deck. If the wave breaks near the shore and reaches the bridge structure as a propagating wave front, the hydrodynamic situation results in high horizontal forces and a sliding failure mode is apparent. When a wave is still in a surging phase and the fluid particles still have their rotational movement, the dominant forcing on the bridge is in vertical direction. Since the vertical force applied to the bridge deck moves from seaside to shore side, the sea side of the bridge deck has a higher vertical velocity which initiates rotation. A seawall causes the water to confine underneath the bridge deck. Which will result in higher vertical forces, thus a rotational failure mode follows. Inclination of the bridge deck has significant effect on the vertical forcing. Positive inclination lead to a decrease of upward forcing and negative inclination lead to an increase of upward forces. The introduction of shear keys resulted in higher moments, since the point of rotation is set at the point the deck interacts with the shear key, which creates a larger distance around the point of rotation. Possible countermeasures that are introduced are a sacrificial beam and a different geometry of the deck. A sacrificial beam was effective in lowering the total horizontal forces on the combined structures. The deck itself was not exposed to a high horizontal impact force. Different geometries are tested to see how the forces on the structure would chance. A wing shaped geometry has positive effects in mitigating the horizontal forces on the bridge deck.

The main motivation within this thesis is to explore the possibility of increasing the service life of box-beam bridge girders to aid the ambition of the Dutch government to become a circular economy. The construction industry still follows a more or less linear economy system. Many bridges in the Netherlands are approaching the end of their service lives, and efforts are being made to extend the lives of these bridges. This is but a temporary solution, and these bridges will require replacement within 20-30 years. This provides an opportunity to incorporate circularity within new and upcoming structures from the design phase onward rather than only as an end-of-life practice. Therefore this thesis explores the possibilities of incorporating the strategy of lifespan extension, in the form of a cover increase against chloride-induced corrosion. The exact increase was calculated through the use of a relevant service life design model (DuraCrete) and compared with the Eurocodes. The reliability of the model was checked using a Monte Carlo simulation. Subsequently, the circular aspects of future adaptability were also investigated considering a fictitious scenario of increased traffic load. Hence, it was concluded that a marginal increase in concrete volume and prestressing steel per beam would allow for a more durable and adaptable beam for the future.

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.

In concrete structures, shear failure is one of the failure mechanisms that should be estimated carefully due to its brittle nature. As the technology advances, the capacity of shear in concrete structures can be calculated with the analytical formulation in codes and standards and simulated with NLFEA. The shear capacity is affected by the size which is a phenomenon observed from experiments where the change in the structure size does not have a linear relation to the structural strength. This can be referred to as the experimental size effect. When estimating the shear capacity with NLFEA, this effect must be included in order to avoid over-estimation of capacity. However, another size effect can be found from the result of NLFEA. The change in structural size has an influence on the global response of concrete structures with different numerical configurations in a simulation with NLFEA. A numerical configuration consists of several numerical parameters. This effect is referred to as the numerical size effect. Therefore, it is necessary to incorporate the experimental size effect and reduce the influence of the numerical size effect in a numerical model in order to increase the accuracy and precision of the simulation with NLFEA. The aim of this study is to investigate how the numerical size effect influences the NLFEA results, which will help understand how to improve the accuracy of the simulation. The investigation is done by studying numerical models with a variation on several numerical parameters, such as load increment, error tolerance, the maximum number of iterations and mesh size. The study is focused on identifying the influence of these numerical parameters for cases with different structural sizes and comparable shear slenderness. This is done by observing the global behaviour of the structure and comparing NLFEA results to their respective experimental results. Any difference in the simulated global response is analysed by observing the difference between the experimental and the simulated crack pattern and the convergence state of the respective step. The study is done in three stages. The study is initiated by investigating how the flexural shear failure mode can be obtained with NLFEA. Two specimens with comparable shear slenderness (a/d), 3.70 and 3.91 for beam A123A1 and H123A respectively, are used as a reference for the simulation model. It was found that bad convergence was achieved at the later stage of the analysis and by not accepting non-converged steps, the results became dependent on the convergence state of the analysis where different peak loads were achieved in different numerical configurations for the same case study. The study continues by identifying the correlation of numerical parameters with the results of NLFEA by creating simulation models with different iterative incremental solutions, load increment, error tolerance, and the maximum number of iterations. All load steps are accepted in this stage, regardless of their convergence state, and the rotating crack model is used in these numerical models. The NLFEA results are post-processed by setting up an upper limit in the error tolerance in order to minimize the variation of the peak load and attain a higher consistency of the results. At the last stage, another study is performed to identify the correlation between mesh sizes with the results of NLFEA by simulating several models with different mesh sizes. All load steps are also accepted in this stage, regardless of their convergence state, and the rotating crack model is used in these numerical models The NLFEA results are also post-processed with the same criteria attained in the previous stage. It is concluded that the results of NLFEA are dependent on the following numerical parameters, the load increment, error tolerance, and the maximum number of iterations, due to different initiations and propagation of dowel crack in the non-converged steps, which influences the convergence condition in the later stage of the NLFEA. The formation and rapid propagation of the dowel crack results in the excessive change in the principal strain direction and magnitude, which induces high relative energy variation and out-of-balance force. These numerical parameters indirectly contribute to the error found in each step in the analysis. An additional study is done by replacing the crack model with a fixed crack model with a damage-based shear retention model, but it was found that this did not solve the problem due to the excessive change in the shear retention factor on the elements that lead to premature failure of the beam. The observation related to the numerical size effect reveals that the mesh size controls the propagation rate of the dowel crack. The use of a smaller mesh size will reduce the propagation rate of the dowel crack after its initiation due to a smaller increment of the crack width between each load step. As a result, the increment of the crack width becomes smaller as the mesh size decrease. This becomes more pronounced due to the effect of excessive change of the principal stress-strain direction and magnitude. Full Newton-Raphson method has been proven to give the smallest variation of the peak load ratio (Pnorm), ranging from 0.887-1.140 for specimen A123A1 and 1.055-1.246 for specimen H123A, compared to the other iterative-incremental method with the use of load increment ratio (load increment/experimental peak load) within 0.03-0.006 in combination with evaluation of acceptable analysis step with error tolerance, where the predefined error tolerance must be set to Gerr = 0.0001 and Ferr = 0.01, and non-converged steps can still be accepted if the relative energy variation and out-of-balance force of the corresponding step are below 0.03 and 0.58 respectively. An additional criterion related to the shear displacement on the major flexural shear crack (Δ) should be added to the evaluation of the acceptable analysis step in order to prevent an excessive crack opening on the major flexural shear crack at the peak load. The analysis step can still be considered valid if the respective step satisfies the criterion of the error tolerance and the vertical crack opening on the major flexural crack on the respective step is below the ultimate tensile crack width (CWt,u), which can be calculated from the Guidelines for Nonlinear Finite Element Analysis of Concrete Structures (Hendriks & Roosen, 2020). A mesh size ratio which larger than h/15 is required to have the correct simulated failure.

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.

Significant development of Jakarta infrastructure is necessary to keep up with the economic growth. For the new Jakarta underground rail network, imminent extension of the North-South Line Phase 1 (NSL-P1) tunnel heads towards the northern part of city. One of the engineering challenges that exist in the area is the substantial amount of reported surface settlement over the years, which is indicated by the continuous sea wall improvement project and the increase of flooded area. The recent GPS survey reported an average subsidence rate of 5 centimeters per year and could reach a maximum of 15 centimeters per year on several hotspots in North Jakarta. Being an underground structure, the rail tunnel would be affected by the settling environment and the reciprocity can be expected. Operational interruptions of the tunnel could occur in the future as a product of differential structural displacement. On the other hand, alterations in settlement rate or pattern must also be anticipated. The aforementioned reciprocity underlines the importance of structural and geotechnical assessments in the area. The assessment then can be used as a reference to determine and improve the safety level of the tunnel as well as the surrounding infrastructures. The study was commenced with the investigation of prevalent driving factors of Jakarta land subsidence from the preceding researches. The initial stage of the study elaborated the concepts used in the analysis, including geotechnical data interpretation, soil consolidation and creep, numerical model formulation, and past studies regarding the loads on bored tunnels. A segment of proposed North-South Line Phase 2 (NSL-P2) tunnel was selected for this study. The selection was motivated by the the amount of available geotechnical information and the severity of differential land subsidence in the respective area. Longitudinal and cross-sectional two-dimensional numerical model of the selected segment were developed in Plaxis 2D, based on the combination of in-situ soil tests and the outcome of earlier studies about Jakarta geotechnical characteristics. Into the model, four time-dependent groundwater level scenarios were assigned to simulate the surface settlement. As the research emphasizes on the long-term settlement, a 100-year study period was chosen and started in the year 2000. Given that the NSL-P2 tunnel design has not been confirmed at the time of writing, the numerical study adopted an identical design to the NSL-P1 tunnel. A 6.65-m diameter concrete tunnel was added into the model at an average depth of 15-m. From the longitudinal numerical analysis, total structural displacement in time and additional longitudinal forces were obtained. Subsequently, further analysis was performed on the cross-section, in the transverse direction, which displayed most settlement at the end of the analysis period. At the cross-sectional perspective, the development of forces as well as soil stress around the tunnel ring due to settlement and structural deformation were acquired. Finally, this study reached a general conclusion which explains that the land subsidence in Jakarta posed non-governing additional loads to the future NSL-P2 tunnel. A majority of the total surface settlement was caused by the consolidation and compression of the upper soil layers. However, special attention must be paid to the station-tunnel interface as substantial differential settlement could take place. To minimize further issues, several design recommendations are provided at the end of the research.

One of the most severe deteriorations in reinforced concrete structures is associated with reinforcement corrosion, where the corrosion distribution shows considerable spatial variability. In the existing investigations of spatial variability of corrosion on the reliability of reinforced concrete structures, symbolic expressions are used for the structural performance. However, structural behaviors like stress redistribution and plasticity spread are not captured. In this research, a computational framework is designed to couple the probabilistic analysis with the nonlinear finite element analysis. Random fields is used with the computational framework to represent the spatial variability of corrosion.A 60 m girder of a reinforced concrete bridge is taken as the case study to explore the effect of spatial variability of corrosion on reliability of static indeterminate reinforced concrete structures. The reliability analysis is target on ultimate capacity of the beam to carry the traffic load. The girder is modeled as a 3 span continuous beam. The modelling of corrosion damages on reinforcement (area of cross section and physical properties) is based on assumption of pure pitting corrosion. In the axial direction of the beam, spatial variability is modeled with random field. In order to study the effect of different level of spatial variability, the correlation length of the random field is set from infinite large to 125 mm. Between adjacent bars, extreme cases of fully spatial correlated and totally spatial independent are studied.The case study shows:i) when corrosion develops, pitting corrosion can severely reduce resistance of the structure and localized damage may lead to a brittle structural response.ii) spatial variability of pitting corrosion in the axial direction of the beam leads to higher failure probability of the structure.iii) spatial variability of pitting corrosion between adjacent bars leads to lower failure probability of the structure.iv) the effect of spatial variability of corrosion on reliability of static indeterminate reinforced concrete structure is a collective effect of probabilistic and physical characteristic.In order to facilitate the reliability assessment of corroded reinforced concrete structures, additional efforts are also contributed to: quantification of uncertainty for the bond model of corroded reinforcement; comparison of various reliability methods with the probabilistic nonlinear finite element analysis framework.The thesis fills the knowledge gap of probabilistic nonlinear finite element analysis of reinforced concrete structures with spatial varied corrosion and quantifies the effects of spatial variability of corrosion on the reliability of a static indeterminate reinforced concrete structure. The analysis framework designed in this thesis is also applicable for other reliability assessment of corroded reinforced concrete structures.

Nowadays, one of the main requirements from civil engineering structures is the level of reliability and safety that they must provide to the users. In structural analysis, the exponential application of numerical methods, as the nonlinear finite element analysis (NLFEA), is due to the increasing growth of computational power. These powerful tools provide the opportunity to study the global behavior of complex systems. The latter is especially relevant for cases where nonlinearities highly impact the performance of the structure. However, to ensure a certain level of safety, the stochastic nature of all the influencing parameters must be accounted for during the analysis and design stages. The latter is precisely the role of Safety Formats: a mathematical procedure to ensure an imposed level of reliability while computing the design resistance of structures. Several existing safety formats have been implemented along with the NLFEA in the structural reliability assessment of reinforced concrete structures. Nonetheless, these formats face some criticism in their usability due to some of the assumptions implied in their derivation. Therefore, Monti et al. (2021) recently proposed a safety format: a new Global Factor Method (GFM) that aims to be applicable in the nonlinear finite element analysis of reinforced concrete structures with concurrent failure mechanisms influencing the global performance at a predefined limit state. In a general description, the method requires the output obtained from two nonlinear finite element analyses and the calculation of a Global Safety Factor related to the resistance of the whole structural system. This thesis aims to provide scenarios to validate the new safety format for its future implementation in codes and the industry since, currently, they are extremely limited. Therefore, the GFM is implemented in three overall case studies with increasing levels of complexity, divided into two reinforced concrete cross-sections, and three simply supported beams. During the case studies, special attention is given to the size of the perturbation (described by the so-called $c$ parameter) that proportionally decreases the basic variables for the second nonlinear analysis. Several Engineer Decision-based Scenarios are applied when choosing the Critical Local Failure Mechanisms and the related basic variables to be perturbed. Finally, it is found that the method provides reliable resistance for structures with a single failure mechanism. However, for structures modelled with continuum elements where two concurrent failure mechanisms lead to global failure, the GFM still needs to be revised to provide more accurate guidelines and reduce the space for decisions made by the analyst that highly impact the performance of the method. These decisions are related to identifying and locating the LFM and their basic variables, selecting the solution strategy implemented in the NLFEA, and choosing a suitable modelling uncertainty. At this point, the application of the method demands an experienced analyst and several parametric studies regarding all those decisions, which reduces its efficiency in terms of engineering and computational time.

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

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

Recently experiments were conducted at the Technical University of Delft on the size effect of concrete. The size effect is a term used for the relative decrease in shear capacity with an increase in height of the structural member. The beams observed in the experiment failed much sooner than was predicted. These test results have implications for the Heinenoordtunnel, the roof of which shares many of the characteristics of the beams that were used in the experiments. The question is posed what happens to the Heinenoordtunnel in case of a fire, when also considering the recent tests on the size effect of concrete. The Heinenoordtunnel is analysed with a numerical model. First however, in order to account for the observed size effect, the beams from the experiment are recreated. A study is performed on the effect of various parameters on the numerically obtained failure load, cracking load, crack pattern and deflection in order to find a set of parameters to approximate the observed size effect. It was found that a significant reduction in tensile strength and fracture energy is necessary to obtain a better approximation of the experimental results. However, despite these changes the numerical model still overestimates the shear capacity. This information is used to create a model of the Heinenoordtunnel. A situation without a fire load is analysed and validated. The model is compared with the analytical IBBC-TNO method. Consequently, the model is subjected to a fire load. The fire is modelled using temperature dependent properties and by determining the temperature ingress for a 2 hour RWS fire. A significant shear crack is found present due the fire load, the location and shape of the crack suggesting onset of shear compression failure. The model however is still considered to be in equilibrium and so failure has not actually occurred in the model. A comparison with an analytical model suggests that a shift in bending moments from the increase in temperature results in a shift of shear capacity in the roof. It is concluded that, while the numerical model does not fail, some caution is advised for the translation of these results to practical application. The change of material parameters found in modelling the size effect tests still leads to an overestimation of the shear capacity. On the other hand, the situation that was modelled was an extremity. In the model of the Heinenoordtunnel the absolute physical maximum water load was assumed in conjunction with an extreme fire. It is recommended to check the fire load with computational fluid dynamics modelling, to see if the fire load could possibly be less severe than assumed.

The Dutch infrastructure counts many bridges, the majority of which are built in concrete. These bridges have been designed and constructed according to safety codes. A lot of these bridges date from the previous century and have been designed conform outdated safety codes. Therefore, the main problem of these bridges is the uncertainty with regard to their structural health as well as their performance under the current loading conditions. The application of ‘smart aggregates’ could potentially solve these issues. Smart aggregates refer to a network of sensors that emit and receive wave signals inside the concrete structure. These sensor are embedded within the concrete and can be implemented in both new and existing structures. The changes in the medium with regard to the stresses are reflected by the phase changes of the wave signal measured by the smart aggregates. This information allows for the monitoring of the conditions of the bridge during its lifespan. The magnitude of the stress in certain parts of the structure could then indicate the need for maintenance at an early stage, thus preventing unnecessary maintenance while preserving the safety of the bridge. This method, however, requires a thorough understanding of the wave propagation inside a concrete medium subjected to a stress state. This thesis investigates how the relative wave-velocity change of a concrete-like medium is influenced by the stresses to which it is subjected. Throughout the report this relation is referred to as the acoustoelastic effect. The first part of the thesis is centered around the theoretical formulation of the acoustoelastic effect. During this study, the models of Murnaghan and Biot have been studied. Subsequently, their differences with respect to the fundamental assumptions have been indicated. Here, it has been found that the main difference between the two models is demonstrated by the way they regard the second-order deformation terms. Murnaghan assumed that these terms are significant and has included them in the constitutive relation. From the latter, Hughes and Kelly have derived expression for wave velocities of a stressed medium, which have been verified with experimental results. On the other hand, Biot adopted the theory of infinitesimal deformations which omits the second-order deformation terms. In addition he based his theory around the wave propagation of a bending rod and extended this model to a three-dimensional medium subjected to initial stresses. This generalisation of an approximated model has led to analytical expressions for the wave velocity of a stressed solid which are contradicted by experiments. From this comparison, it has been concluded that Murnaghan’s model results in the most accurate representation of the acoustoelastic effect. The second part of the thesis focuses on the verification of the theoretical acoustoelastic effect through experimental research. For the purpose of verifying the acoustoelastic effect as well as determining the third-order elastic coefficients of a concrete-like medium, four specimens have been tested. In order to investigate the influence of the inhomogeneity of the material on the changes in the wave velocity, two different material compositions have been investigated. The first type consists of a homogeneous cement paste, whereas the second type represents heterogeneous concrete including aggregates. During the experiment, the different waveforms have been repeatedly emitted through a specimen subjected to an uniaxial compression. The relative wave-velocity change has then been obtained by post-processing the acquired data, which has been compared with Murnaghan’s model. The conclusion of this research is that Murnaghan’s theory can be used to accurately predict the relative wave-velocity changes of the cement-paste specimens, and in particular the relative P-wave velocity changes. The results have shown that the radial recordings yield inconsistencies which can be attributed to the small dimensions of the specimens. Furthermore, the influence of the inhomogeneity of the material on the relative wave-velocity changes manifests itself through a discrepancy in the acoustoelasticity. Here, it is found that the ratio between the aggregate size, the specimen dimensions and the wavelength of the signal determines the sensitivity to the acoustoelastic effect. Therefore, before the data from the smart aggregates embedded in a real structure can be interpreted, the experiments need to be improved and expanded. It is important to investigate the acoustoelasticity of waves with non-orthogonal propagation and particle-oscillation direction, while applying various stress states to the medium. This is because the smart aggregates are arranged in a network, where the signals are emitted signals are propagating through the structure via arbitrary paths between various transducers.

Application of Nonlinear Finite Element Analysis (NLFEA) is lagging behind the many digital advances in the structural engineering practice. This is due to the need for codes and standards. To help development of these codes and standards, 119 solution strategies were developed with different assumptions and choices for the concrete constitutive model, the finite element discretization, the way of modelling the reinforcement and the incremental-iterative procedures. The constants aspects of the constitutive model, like confinement and the reduction compressive strength due to lateral cracking, are based on the RTD1016 Dutch Guideline. All models are two-dimensional with a plane stress assumption and in all cases the analysis is force controlled with the application of an arclength method. This is done to increase the value of results for application in practice, as generally displacement loading is hard to apply in a real-life structure. The strategies were benchmarked with 101 experiments on reinforced concrete beams selected from literature. Those beams cover a broad range of design aspects, failing both in shear and bending, reinforcement configurations with- and without shear reinforcement, both prestressed and conventional reinforcement and heights ranging from 90 to 1200 mm. This resulted in 1919 NLFEAs which were performed with an automated approach in the DIANA multi-purpose finite element software package. It was concluded that the failure load and failure mode of the experiments can be approximated with a mean uncertainty of 1.05 with a coefficient of variation around 10 percent, provided that an appropriate solution strategy is applied. It is possible to assign an appropriate solution strategy when the structural design is known, where the main influence is the presence of shear reinforcement. Beams with stirrups are robustly modelled by a rotating crack model, while beams without stirrups were found to be better approximated by a fixed crack approach with specific choices regarding reinforcement modelling and equilibrium. To have a more objective way of judging the ductility of a failure, a measure of the dissipated energy in the reinforcement was implemented in the DIANA code. It was found that the mean model uncertainty of a ductile failure can be as low as 1.045, with a coefficient of variation around 10 percent. Brittle failures showed a mean uncertainty of 1.131, with a coefficient of variation just below 16 percent. Therefore the ductility index was found to be a valid way to judge the reliability of an NLFEA result. This study has demonstrated the applicability of force controlled NLFEA for reinforced concrete beams. The derived properties of the model uncertainties are a crucial input for safety formats.

For calculation of the resistance of a composite slab against the transverse shear force, the Eurocode 4 (composite structures) simply refers to the calculation procedures of the Eurocode 2 (concrete structures). It is assumed that the composite slab consists out of a consecutive range of concrete ribs in its width direction, which are solely responsible for resisting the transverse shear force. To calculate the transverse shear capacity of these concrete ribs, an empirical formula is used that was originally derived for regular reinforced concrete beams (without stirrups). However, the concrete ribs of the composite slab are created by the profile of the steel deck, making that each concrete rib is accompanied by two steel webs on the sides. According to the Eurocode 3 (steel structures), these webs of the steel deck have their own transverse shear capacity, which is neglected by the current design approach defined in the Eurocode 4. Besides, the interaction between the steel deck and the concrete may lead to an even higher transverse shear capacity of the composite slab. In this thesis, the aforementioned two aspects, which are currently overlooked by the design principle of the Eurocode 4, are further studied by means of non-linear finite element modelling. The validation of this empirical formula of the Eurocode 2 for calculating the transverse shear capacity of the concrete ribs is the first point of interest. From the finite element analysis (FEA) of the concrete section of ComFlor 210, it is concluded that the prediction of the transverse shear capacity by the Eurocode 2 is unnecessarily conservative. The study suggests to use the mean width of the concrete rib (b0) in calculation, instead of the minimum width in the tensile area of the concrete rib (bw), as an improvement to the method of the Eurocode 2. In the next stage, the contribution of the steel deck to the transverse shear capacity of the composite slab is studied. The exact bonding properties between the steel deck and the concrete (at the interface) were not clear when the finite element model was developed, so some assumptions had to be made. When assuming that the steel deck can’t separate from the concrete and the relative slip is restrained in longitudinal direction by the embossments, an increase of 131.6% in transverse shear capacity is found. Because of the assumed interface properties, the steel deck contributes to the total transverse shear capacity in the following ways: it resists a part of the transverse shear force in its webs; it acts as reinforcement to the concrete like a longitudinal rebar; it acts as reinforcement to the concrete like stirrups. However, whether this stirrup-functioning of the steel deck’s webs is representative for the actual transverse shear behaviour of deep composite slabs is being questioned, because it relies on the assumption of no separation at the interface. Therefore, a second FEA of ComFlor 210 is executed in which the interaction between the steel deck and the concrete is neglectable. Still, an increase of 51.4% in transverse shear capacity is found, which can be considered as a lower bound value. At last, from the FEA results of this thesis, it can indeed be concluded that the current Eurocode 4 provides a unnecessarily conservative calculation method for the transverse shear capacity of ComFlor 210. However, using a simple engineering model that adds up the partial resistances of the concrete ribs and the steel deck’s webs, gives a better prediction while still being safe. For the partial resistance of the concrete ribs, the empirical formula of the Eurocode 2 is used, but this parameter bw is substituted by b0 as already mentioned in the foregoing. For the partial resistance of the steel deck’s webs, the procedures of the Eurocode 3 are followed.

The shear capacity of concrete members is a major challenge of structural concrete research through the years. Many theoretical models have been developed and various experiments have been performed, focusing on the accurate prediction of the shear behavior. Many of the available theoretical models assume that a large contribution of the shear capacity is transferred through cracks by a mechanism often recognized as aggregate interlock. At the same time, due to the increase in the complexity of the structures and the development of the concrete technology, the mechanical properties of concrete have improved significantly. This fact leads to the need for modification of the existing models or the development of new ones, accommodated to the improved materials. Since, the aggregate interlock plays a significant role in the development of the shear capacity, the present research proposes a new numerical methodology for the calculation of the aggregate interlock in high strength concrete in which aggregates break, based on the widely recognized model proposed by Walraven and the results of direct surface roughness measurements. The crack surfaces of concrete cylindrical specimens drilled from a 70 years old existing concrete bridge and newly casted cubic specimens generated by splitting tensile tests were measured by a laser scanner. Moreover, the surface of a reinforced deep beam after flexural shear failure was measured as well. The measured crack surfaces were used to implement the plasticity based aggregate interlock model proposed by Walraven with an algorithm which was validated with Walraven’s theoretical model, using a so-called mesostructural model. The output of the analysis gave suggestions on the adjustment of the available aggregate interlock model for high strength concrete. The proposed model is then implemented into a shear test on a 1.2 m concrete beam, which has a concrete strength larger than 70 MPa and the aggregate interlock seems to influence significantly the shear resistance of a cracked section. Based on the observation of the surface roughness of a crack, the thesis further proposed that with a sufficiently large crack face, the localized variation in the crack surface is averaged out. Thus, the surface can be used to develop a master curve for the given concrete type. In the last part of the study, two improvement suggestions are given regarding the Critical Shear Displacement Theory. The one point is relevant to the simplification of the crack profile that can be changed from a straight line into a more inclined and the second point is related to the correction factor considering the fracture of the aggregates, that should be dependent on the crack width.