Steel has typically been used in the sluice gate design for well over a century. However, the development of ultra-high performance fibre reinforced concrete (UHPFRC) in the recent decades has presented an interesting alternative to traditional steel sluice gates. The appeal of UHPFRC is based on its extraordinary durability and resistance to most forms of corrosion. Gates produced with the material could function without the need for replacement or maintenance works for extremely long periods of time. Due to higher material strength parameters, UHPFRC elements are also significantly more slender and therefore lighter than their standard concrete counterparts. That makes UHPFRC a potential alternative to traditionally used steel.
A UHPFRC mitre gate had already been designed as a replacement for one of the gates in the Robbengatsluis complex. However, due to the novelty of the solution, there were concerns about whether the design choices and solutions used in the process may have resulted in an overly conservative design. The goal of the project was to redesign the UHPFRC gate, verifying if a more optimal design was possible and which of the available methods of analysis were most suitable in the context of UHPFRC sluice gate design.
The gate’s design was focused around the concept of a plate gate strengthened on its inner side by beam segments running along the edges of the structure and through its most significantly loaded areas. In the project, two main approaches were considered. The first focused on reviewing the analytical design procedure used for the original design. The applied standards and assumptions were reassessed, leading to modifications such as the adoption of alternative analytical formulas, the inclusion of fibre contribution in relevant limit states, and the adjustment of the fibre orientation factor for thin plate segments. Relevant ultimate limit state (ULS) and serviceability limit state (SLS) verifications were conducted. This approach was supported by linear finite element analysis as a conservative estimation of the structure’s behaviour.
The second approach aimed at incorporating nonlinear finite element analysis (NLFEA) to verify the accuracy of the utilized analytical design methods. Additionally, the application of NLFEA allowed for consideration of load redistribution effects, which are of significance in the case of UHPFRC structures. Material tests (compression tests, 3-point bending tests, etc.) had been conducted to prepare the NLFE model of the considered UHPFRC mix and to evaluate material parameters utilized in the analytical design verifications. The nonlinear approach was based on a total strain-based rotating crack model. Two nonlinear numerical solution strategies were developed, one based on plane stress elements and the other based on shell elements. The solution strategies were validated within the framework presented in Model Code 2020. The plane stress element solution strategy was validated by comparing numerical simulation results with literature-based results from 4-point bending tests of reinforced UHPFRC beams. The shell element-based strategy was validated by comparing numerical simulation results with experimental data from one-way plate bending tests conducted by FDN Engineering. It was evaluated that both solution strategies closely predicted the experimental results. The modelling uncertainty of the plane stress element strategy regarding prediction of beam bending capacity was quantified through the application of Global Factor Method. The strategy was then used to evaluate the bending capacity of all beam segments within the structure. The shell-based solution strategy was used to take into consideration load redistribution effects in the critical plate segment.
The numerical results confirmed the accuracy of the applied analytical verifications. Numerical capacities differed from analytical ones by -5.7% to +4.4%, they gave more conservative predictions for low reinforcement ratios and less conservative ones for high reinforcement ratios. Due to the lack of experimental benchmark data for UHPFRC plate segments, nonlinear numerical analysis could not be used to comprehensively evaluate the load redistribution effects for the structure at large, as the modelling uncertainty of the solution strategy could not be estimated. A new design for the UHPFRC mitre gate was prepared based on the revised analytical approach. Among other changes, the new design included altered aspect ratios of beam segments and reductions in segments’ reinforcement. The original design and the new design were compared in terms of the amount of concrete and reinforcement used. The new gate variant required slightly less UHPFRC and significantly lower shear and longitudinal reinforcement ratios, with the total decrease in the amount of reinforcing steel reaching 56.2%.
Reinforcement design was strongly influenced by crack width SLS verifications, which required significantly higher reinforcement ratios than ULS requirements. The dominance of crack width SLS was high enough to nullify any potential benefits from less conservative ULS verification approaches. A review of available information suggested that the applied MC2020 SFRC crack width SLS verification could be improved upon to provide less conservative estimations by either utilizing a UHPFRC-specific code-based analytical verification or applying NLFEA in the process.
The concluding results can be used as a reference point for future attempts at designing UHPFRC mitre gates. Currently available UHPFRC and SFRC design standards provide a good framework for the design of those elements, with significantly reduced material use compared to the previous design. With superior durability, UHPFRC offers a feasible alternative to the use of steel. The proposed plate and beam segment structure is a viable solution for UHPFRC mitre gates of similar dimensions. Efficient design requires a series of material tests to properly quantify the necessary input parameters and the benefits of the utilized material on a case-by-case basis. The new design simplifies manufacturing and improves efficiency without compromising performance. ... Read more

The Netherlands faces an urgent housing shortage, especially in urban areas where demand outpaces supply and space for new development is limited. Modular construction presents a scalable and efficient solution, yet its application in mid-rise buildings up to 70 metres remains constrained by unresolved structural challenges, particularly regarding lateral stability, connection behaviour, and collective module behaviour. Previous research acknowledged the individual potential of outrigger elements and tie-rod connections to enhance stability, but their combined integration in a modular mid-rise context had not yet been fully explored.

This thesis addresses that gap by developing, analysing, and validating a hybrid structural concept in which corner-supported steel modules actively contribute to the building’s lateral load resistance. The proposed system integrates tie-rods and steel outriggers with a precast concrete core to transform the modular units from passive vertical load carriers into active components of the lateral stability system. To assess this system, a four-phase research strategy was adopted, including a feasibility study, concept development, structural optimisation, and a final 3D case-study application. A key methodological decision was the use of parametric modelling tools, Grasshopper and Karamba3D, to enable rapid iteration and flexible structural analysis across design alternatives.

The analysis demonstrated that, in a 20-storey structure, the integration of two outrigger levels (floors 7 and 14) reduced top displacement by 13.5% compared to a core-only structure. The structure reached a height of 67.7 m while satisfying the H/750 serviceability criterion. Member utilisation levels remained below 1.0, and tie-rod forces stayed within feasible limits. However, the effectiveness of the proposed concept was significantly influenced by axial elongation of the tie-rods: M24 tie-rods reduced outrigger effectiveness to 17.7% compared to 25.4% in the idealised case without elongation, while M50 tie-rods improved performance to 20.5%. Parametric studies further showed that outrigger effectiveness depends strongly on the stiffness of the concrete core. With a flexible core, outriggers reduced lateral displacements by over 30%; this benefit dropped below 10% for stiffer configurations, underscoring the importance of a balanced stiffness distribution between core and outriggers to maximise the effectiveness of the proposed concept.

These findings demonstrate that the proposed hybrid concept is a viable solution for modular mid-rise construction, enabling greater design heights while maintaining structural efficiency. The innovative use of parametric modelling not only enhanced design flexibility but also accelerated the evaluation process. The research contributes a validated structural concept that addresses current limitations in modular design and provides a foundation for further innovation in hybrid modular systems. ... Read more

Induced seismicity has been an issue in the area of Groningen in the north of the Netherlands. Due to gas extraction from the Groningen gas field, these induced earthquakes have occurred more frequently, especially since large-scale extraction began in the 1960s. Following the reduction of gas extraction since 2018, a slight decrease in the number of induced earthquakes has been observed. Nevertheless, severe damage to buildings in the Groningen area remains a significant risk. The building stock is largely composed of unreinforced masonry (URM) buildings, which were not designed according to a seismic code. These buildings were originally designed for wind resistance, providing limited lateral capacity, and making them vulnerable to earthquake forces.
The assessment of the seismic behaviour of unreinforced masonry has been extensively studied at Delft University of Technology. Within the framework of a large-scale testing campaign, a quasi-static cyclic pushover test on a masonry assemblage was performed at the Stevin II laboratory of Delft University of Technology. This experimental campaign was designed to serve as a benchmark for both numerical and analytical models. The masonry assemblage, chosen to represent a typical terraced house built between 1960 and 1980 in the Groningen area, consists of calcium silicate masonry walls and concrete floors. Thereafter, finite element models were created to reproduce the experimental results. However, relying on a single configuration limits the study, and additional cases will be studied numerically in this work to explore a wider range of geometric variations. ... Read more

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

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

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

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

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

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

The Great Portico of Medina Azahara is a prominent remnant of the 10th-century Caliphate of Córdoba. Once the monumental entrance to the Caliph’s palace complex, it is now a partially preserved four-arched masonry structure. The site is a UNESCO World Heritage monument of major cultural significance. This study investigates the seismic response of the existing remains of the Great Portico using finite element modelling and nonlinear pushover analysis. It aims to identify its dominant vibration modes, primary failure mechanisms, and the points of concern for damage due to seismic loading. The study adopted a continuum homogeneous modelling strategy. Multiple three-dimensional finite element models were constructed in an iterative approach. Due to lack of in-situ measurements, the model geometry was approximated based on detailed drawings of the structure. Three building materials were defined: limestone masonry, brick masonry and limestone. Boundary conditions fixed the column bases, and loading consisted of the self-weight followed by a modal pushover analysis. The dominant eigenmodes were determined using an eigenmode analysis. Both the in-plane and out-of-plane responses of the structure were analysed. The in-plane response is characterized by tensile cracking in the arches’ brick masonry and at the interfaces between brick masonry and limestone blocks. The out-of-plane response had the most critical failure mechanism. Cracking in the limestone masonry initiated at the bases and mid-height of the columns, leading to tensile failure and toppling of the second arch. However, the overall capacity of the Great Portico, estimated at approximately 1.0 g, is relatively high compared to results from shake-table tests on masonry structures. Sensitivity analyses demonstrated that halving the tensile strength had minimal influence on global capacity, while reducing stiffness decreased peak base shear but did not alter failure modes. Crushing was observed only at high displacements, well after tensile cracking dominated the response, confirming that tensile failure controls the seismic vulnerability. In conclusion, this study indicates that the remaining part of the Great Portico is most vulnerable under out-of-plane loading, leading to tensile cracking in the limestone masonry of the columns. The in-plane response, while stronger, is controlled by cracking within the brick masonry in the arches and at the interfaces between the brick masonry and limestone blocks. Crushing failure is not governing for both mechanisms. ... Read more

Concrete structures are responsible for a substantial share of the total global CO2 emissions. This has led to the establishment of the Betonakkoord in the Netherlands, which aims to significantly reduce the emissions from concrete structures.

Reinforcement bars made from Basalt Fibre Reinforced Polymer (BFRP) offer a potential solution for making concrete structures more sustainable. Firstly, the Environmental Cost Indicator (ECI) of BFRP rebar is 43% lower than that of steel rebar. Additionally, BFRP does not corrode, which eliminates the requirement for a thick concrete cover to meet environmental class standards. Consequently, the use of BFRP reinforcement instead of steel could potentially reduce the amount of concrete needed, further enhancing the sustainability of concrete structures.

This study investigates the feasibility of enhancing the sustainability of a bridge deck in an inverted T-girder bridge by using BFRP rebars. BFRP differs from steel in several material properties. Although its strength, at approximately 1200 N/mm², is significantly higher than that of B500B steel, the much lower E-modulus of BFRP presents challenges. Additionally, BFRP behaves in a fully linearly elastic manner until failure in the absence of a yield plateau. The lower stiffness results in higher deformations and crack widths. The hypothesis is that this could potentially be problematic for shear capacity, as the concrete compression zone is reduced, aggregate interlock decreases, and dowel action is less effective due to the low transverse strength of the rebar.

In this study, various design variants for a bridge deck in an inverted T-girder bridge were modeled to assess the impact of different design parameters. A reference design variant with steel reinforcement was used as a baseline and compared with several variants incorporating BFRP rebars. The BFRP design variants differed in terms of reinforcement quantity, concrete cover, and effective depth.

A quasi-linear model of an inverted T-girder bridge was developed using the numerical software SCIA Engineer. The bridge deck design alternatives were modeled as an orthotropic plate with centroidal ribs. The numerical model clearly demonstrated that, due to the less stiff nature of the BFRP-reinforced bridge decks, there is less distribution of traffic loads compared to relatively stiff steel-reinforced bridge deck. Ultimately, the model showed that shear force is indeed the critical failure mechanism for BFRP-reinforced bridge decks. Reducing the effective depth of the BFRP reinforced bridge deck variants, decreases the shear force distribution in transverse direction by 5% and further decreases the shear capacity by 23% to 30%, depending on the adjusted parameters for each design variant.
The application of BFRP rebar in a bridge deck and the reduction of concrete cover to 25 mm, instead of the usual 50 mm used with steel reinforcement, is shown to be feasible in this study. An optimization was conducted to develop a bridge deck design, that meets the structural performance criteria of shear force while minimizing concrete usage. This resulted in an optimized design with a bridge deck height of 215 mm, compared to the conventional 250 mm.

A sustainability study based on the LCA cradle-to-gate life cycle phases (A1-A3) has demonstrated that BFRP reinforcement can significantly enhance the sustainability of a bridge deck. For the optimized design variant that meets all the structural requirements, the ECI reductions range from 27% to as much as 32%, depending on the cement type used in the concrete mixture. This study has shown that the application of BFRP rebars in a concrete bridge deck is certainly feasible and results in significant sustainability improvements. ... Read more

Alkali-Silica Reaction (ASR) poses a significant challenge to the durability and structural integrity of reinforced concrete structures worldwide. This thesis presents a comprehensive modelling framework that integrates numerical simulations and phenomenological models to predict the long-term behaviour of ASR-affected structures. The framework addresses the progressive degradation of material properties and the structural implications of ASR-induced expansion, using expansion characteristics derived from experimental data.
Several numerical methods exist to simulate ASR effects at the structural scale. Among these, the Dual Mesh Method (DMM) stands out as novel pre-damage method to simulate ASR induced damage in reinforced concrete. Building upon this approach, this research develops the Modified Dual Mesh Method (MDMM), introducing key advancements such as an adapted tensile curve (ATC) to enhance its predictive capabilities.
The MDMM was validated numerically against reinforced concrete beam behaviour, demonstrating its effectiveness in simulating ASR-induced stress generation, crack propagation, and material degradation under incremental expansion conditions. A comparative analysis with the Reduced Material Properties Method (RMPM) highlighted the MDMM's effective ability to account for internal expansion forces and anisotropic behaviour influenced by structural configurations. The results confirmed the framework's accuracy in replicating critical structural responses such as crack propagation patterns and load-deflection behaviour.
Phenomenological models by Larive and Esposito were integrated into the framework, linking ASR-induced expansion with time and material property degradation. These models enabled long-term damage simulations and were applied to a hypothetical bridge pier cap. The simulation successfully captured key aspects of ASR-induced damage, including crack alignment with reinforcement, stress redistribution, and reinforcement yielding, providing insights into the service life thresholds of ASR-affected structures.
While the framework demonstrates promising capabilities, it remains in an early development stage. Limitations were observed, particularly in accurately representing the gradual reduction of elastic modulus associated with ASR progression. Further validation with complete case studies and exploration of diverse structural configurations are recommended to enhance its applicability and reliability.
This research offers a valuable tool for structural assessment, maintenance planning of ASR-affected infrastructure, bridging the gap between experimental observations and predictive modelling of long-term structural performance.
... Read more

This research focuses on comparing Accoya® with unmodified wood and investigates Accoya®’s structural performance in environments with varying relative humidity levels. The wood’s moisture content, and consequently its swelling and shrinking behavior, fluctuates on an annual basis due to these varying relative humidity levels, especially when exposed to outdoor conditions. FEM analyses were conducted to investigate physical properties and the performance of moment-resistant connections, with their implementation aimed at incorporating rotational stiffness into a structural portal frame. Accoya® demonstrates excellent moisture resistance and an increase in dimensional stability of approximately 80%, based on Dutch climate conditions. The reduction in swelling alleviates internal stresses within the connections, enhancing the strength and stiffness of moment-resisting connections. Specifically, a clamped connection and a circular dowel connection were analysed using a linear elastic static FEM model, revealing internal stress reductions of 81% and 52%, respectively. This reduction was observed during the simulated initial annual swelling cycle that the wood may undergo. With the use of Accoya®, significantly less plastic deformation is expected in connections due to swelling issues compared to unmodified wood and reduced deflection in structures is expected. An increase of 219% and 58% in rotational stiffness was observed for the respective cases. To evaluate the impact on overall stiffness, these observed values were implemented in a portal frame structure. A reduction in horizontal displacement was observed ranging from 31% to 66%. This opens up new possibilities in structural wood design, allowing for slimmer and lighter wood constructions. Due to Accoya®’s lower property degradation and more stable structural performance in high-humidity conditions, an adjustment of the kmod and kddef factors is suggested; however, this is not sufficiently substantiated in the current study. Future research could explore long-term performance factors with experiments such as creep and fatigue to validate Accoya®’s structural reliability further. ... Read more

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

This thesis investigates the potential of Basalt Fibre-Reinforced Polymer (BFRP) as an alternative to traditional steel reinforcement in concrete structures, with a focus on enhancing shear capacity. BFRP offers advantages such as higher tensile strength, superior corrosion resistance, and environmental sustainability. The study compares two alternative BFRP stirrup designs—braided BFRP rods and laminated unidirectional (UD) BFRP strips—with traditional steel stirrups through uniaxial tensile testing and displacement-controlled three-point bending tests on reinforced concrete beams. The results show that while BFRP stirrups improve the shear capacity of concrete beams, they do not yet match the performance of steel stirrups due to issues like reduced stiffness and stress concentrations in corner sections. However, BFRP stirrups demonstrated potential advantages in terms of weight efficiency, suggesting a promising role in sustainable construction. The findings underscore the need for further refinement in BFRP production methods to achieve consistent quality and better performance in structural applications. ... Read more

There are about 70 prestressed concrete T-beam girder bridges built between 1953 and 1970 in the Netherlands. Ensuring the safety of these existing bridges under current traffic conditions is
imperative. Upon initial assessment of these existing prestressed concrete T-girder bridges, half of them didn’t meet the safety requirement specified by the design code even though they didn’t show any sign of distress during inspection. This is because the system behaviour of the T-girder bridges (i.e.) load transfer mechanisms such as CMA (compressive Membrane Action) and load redistribution were not considered, which could potentially increase the calculated strength capacity of these existing bridges. Therefore, a computationally efficient method for evaluating these bridges is needed.
This research addresses the challenge of accurately predicting the strength capacity of prestressed concrete T-girder bridges using a computationally efficient approach. The study involves modelling the 2D bridge deck in the horizontal plane using orthotropic plate elements and 2D individual girders in the vertical plane with non-linear material properties. The 2D bridge model was compared with a 3D linear bridge deck model, showing a variation in bending moment between 10% to 13%, sufficient for studying load effects. The 2D individual girder model built was validated using experimental data of the disconnected T-beam test of the Vecht Bridge, incorporating a quasi-Newton solution method with the Broyden-Fletcher-Goldfarb-Shanno (BFGS) algorithm. The predicted load versus deflection curve from the 2D non-linear individual girder model closely followed the load versus deflection curve obtained from the experimental test results. To combine the 2D bridge deck model with the 2D non-linear individual girder model, an equivalent loading technique was developed by numerically solving the shear force distribution of the critical girder in the 2D bridge deck model. The staggered 2D Non-Linear Finite Element Approach developed utilising the equivalent loading technique accurately predicted the ultimate failure load of the connected T-beams (system behavior) within 10% of experimental values, despite neglecting the effect of end crossbeams. The 2D bridge deck model without considering crossbeam effects showed conservative stiffness estimates. Crossbeam inclusion in the model indicated significant improvements in stiffness, load distribution and redistribution. The 3D non-linear finite element model predicted 87% to 95% of the failure load of the connected T-beam tests [10]. The 2D non-linear individual girder model using the staggered non-linear approach predicted up to 96.5% of the ultimate failure load of the connected T-beam test, achieving this with a run time of approximately 18 to 21 minutes. Overall, the staggered 2D Non-Linear Finite Element Approach developed shows promise for preliminary bridge safety assessments offering a balance between computational efficiency and accurate prediction of strength capacity.
... Read more

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

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

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

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

In the more than sixty years of experience in forensic structural engineering of Adviesbureau Hageman, damages in underground concrete parking structures repeatedly passed by. In a master study, mainly based on the comprehensive archive of Adviesbureau Hageman, an overview of the various damages that can be distinguished, is made and causes for the occurrence and measures to prevent them, are addressed. Furthermore, one category of damages, that is not limited to only parking structures, but generally occurring in concrete structures, is damage to concrete corbels. In order to investigate the behaviour of such corbels, finite element analyses are performed with the FE Code ATENA. Its behaviour in case of a corbel and support according to the Codes is investigated, but also in case of a support close to the edge and applied horizontal loading due to imposed deformations in the elements that are supported by the corbel. In the thesis the overview of damages in concrete parking structures and the study into the behaviour of corbels will be presented. ... Read more

Concrete is widely used in civil engineering and despite its long history, accurate prediction of the hardening process, particularly in partially restrained conditions, remains a challenge. During the hardening of partially restrained concrete, residual stresses occur due to restrained deformations caused by factors such as heating/cooling and shrinkage of the concrete. Accurately predicting the development of these residual stresses during restrained hardening is critical for proper design calculations, as cracking must be controlled by reinforcement. However, predicting the development of these design stresses is complex and depends on a number of processes and parameters, including temperature development, development of mechanical properties and the degree of restraint. These stresses also decrease with time due to creep and relaxation, which further complicates predictions, especially when dealing with restrained concrete combined with shrinkage.

In addition, hardening concrete will eventually be subjected to external loads, resulting in additional stresses that may require additional reinforcement. However, when it is difficult to accurately predict the development of design stresses, approximations must be made. These approximations may either take full account of the stresses from both hardening and external loading, or reduce the residual stresses by some factor. Such factors may be based on design codes or rough estimates. Consequently, these approximations can lead to either over- or underestimation of the reinforcement required in the design, mainly due to a lack of understanding of the actual design stresses. Therefore, the research question investigated in this thesis is as follows:

What is the effect of applying time-dependent finite element analysis, including the combination of hardening processes and external loads, on improving the prediction of the development of design stresses for partially restrained concrete?

The research starts with a comprehensive literature review covering the stress development during hardening of restrained concrete, the current calculation methods and models and a validation experiment. The validation experiment, a Temperature-Stress Testing Machine (TSTM) found in literature, is modelled and the analysis results are compared with the experimental results to validate the accuracy of modelling the hardening of partially restrained concrete. A method is developed to accurately predict the hardening of restrained concrete using a combination of transient heat transfer analysis and structural non-linear analysis. This non-linear analysis uses a combination of time and load steps to apply the required degree of restraint. The finite element analysis, using measured thermal and material properties from the literature, shows good agreement with the TSTM experimental results.

In order to verify the accuracy of commonly used material models, the Eurocode and fib Model Code material models within DIANA FEA are compared with the results of the TSTM experiment. However, it was found that these material models have inaccuracies due to the use of large step sizes for the Kelvin chains that define the creep and Young’s modulus developments. Therefore, a viscoelastic material model based on the fib Model Code was developed and found to be more accurate. This material model was validated against the TSTM experiment and hand calculations. Although differences were found in the development of design stresses between the experimental results and the prescribed standards, these were mainly due to the difference in autogenous shrinkage and coefficient of thermal expansion.

Using the knowledge gained from the modelling of the TSTM experiment and the validated viscoelastic material model, a case study of the railway underpass in Leiden is performed. The chosen modelling approach is a time-dependent non-linear finite element analysis that includes all construction phases, hardening processes, and external loads within a 3D model of solid 3D elements. The model excludes concrete cracking, reinforcement and prestressing of the deck to limit complexity. This calculation method is expected to provide a more detailed insight into the development of design stresses and ensures high calculation accuracy and completeness compared to other methods. The use of a full 3D model was necessary to accurately model the temperature development in the hardening concrete, which has a significant effect on the design stresses…
... Read more

Traditional approaches to noise barrier design often rely on outdated techniques and resource-intensive materials like concrete and steel. However, with sustainability gaining prominence, aligning noise barrier design with green construction principles becomes crucial. Structural optimization, aimed at minimizing material usage, emerges as a promising strategy to mitigate environmental impact. This study focuses on determining the optimal geometry of a noise barrier composed of low-tensile strength material, under the influence of self-weight and uniformly distributed lateral load.

The methodology employed addresses this question through a series of key steps. Beginning with a two-dimensional analytical form-finding process, optimal cross-sections are derived for the noise barrier. The application of uniform strength theory, known for its efficiency in generating material-effective structures, results in constant stress shapes. These solutions are validated using Finite Element Analysis (FEA) to ensure conformity with predefined stress criteria. Subsequently, numerical structural optimization is conducted to achieve minimum weight geometries that adhere to stress constraints, utilizing a penalty function. The validation process involves comparing numerically optimized geometries with analytical solutions, confirming their reliability and mutual consistency. This validated optimization approach is then extended to three dimensions, exploring the optimal combination of longitudinal profiles and varying cross-sections along the barrier.

Analytical solutions for 2D uniform strength cross-sections of the noise barrier differ based on load conditions. For self-weight, an exponential function describes constant stress, ensuring uniform compressive stress across the structure. Conversely, under uniformly distributed lateral load, a linear function depicts constant maximum bending stress along the height. The interaction between self-weight and lateral load results in symmetric geometries defined by specified constant tensile stress. A square root geometry guarantees constant zero tensile stress, offering advantages like reduced need for additional structural elements and practicality in real-world scenarios.

A significant distinction arises between 2D cross-section and 3D structural optimization regarding bending capacity. In three dimensions, the entire structure contributes to bending resistance by shaping itself. Releasing the rotational degree of freedom at the bottom support enables the generation of a corrugated longitudinal profile, enhancing bending stiffness. This corrugation distributes bending moments over longer spans, reducing stress and material requirements. Notably, the optimized corrugated profile exhibits enhanced bending stiffness, minimizing the impact of practical constraints.

In summary, this research provides insights into optimal geometries for free-standing structures, highlighting the efficiency of analytical and numerical approaches. The numerical optimization framework proves highly effective and efficient, contributing valuable insights to noise barrier design within a sustainable framework. ... Read more

Previous earthquake reports have highlighted the high vulnerability of masonry walls to failure when subjected to the out-of-plane (OOP) loading. Particularly, this OOP failure is a significant cause of collapse in unreinforced masonry (URM) buildings, especially those with slender walls and large openings. Moreover, in the past they were designed with minor regard to seismic design concepts. In Groningen, the Netherlands, where the majority of houses are constructed using unreinforced masonry, there have been frequent occurrences of low-intensity seismic activity, causing pre-damage to the walls. Typically, the walls get pre-damaged in the in-plane (IP) direction due to low-intensity shakes and settlements, since the box-like behaviour is established when the forces are low. Box-behaviour refers to the case where there is a strong connection between orthogonal walls and a stiff rigid floor diaphragm. As a consequence, the walls experience the desired IP shear failure during seismic loading. However, research regarding the OOP performance of pre-damaged URM walls is limited, and existing studies have shown that IP pre-damage decreases the ultimate OOP load-bearing capacity of the walls. To address this gap, this report aims to conduct a preliminary investigation on the OOP strength of pre-damaged URM walls, considering both walls without and with openings. Notably, there is no existing evidence in the literature regarding walls with openings on this specific topic. The primary research question can be stated as follows:
How does the in-plane pre-damage affect the out-of-plane load-bearing strength of URM walls?

This thesis employs a numerical modelling approach to address the research question. The software package DIANA 10.5 is used, adopting a simplified micro modelling method with shell elements to simulate the behaviour of masonry. Bricks are modelled with continuum shell elements, while the mortar joints are modelled using zero-thickness interface elements. Also, the potential vertical crack in the bricks is considered using the interface elements. The validation of the numerical modelling approach is performed in two steps. Firstly, the mechanical properties of the numerical model are calibrated using small-scale material tests. In the second step, the calibrated parameters are directly applied to the numerical monotonic analyses of full-scale walls, and the results are then compared to experimental test results. The calcium silicate (CS) brick masonry tests, from material to structural levels, conducted at the Delft University of Technology are selected as benchmarks for the calibration and validation of the numerical model. A good agreement is observed between the numerical and experimental results for the IP walls in terms of initial stiffness, peak shear force, and crack patterns. However, the results for the OOP walls are significantly overestimated, with an average overestimation of 35% for the peak force. This is attributed to the differences in boundary conditions (full or partial rotation restriction), type of tests (cyclic or monotonic) and loading conditions (displacement control or load control) between the numerical simulation and experimental tests. Nevertheless, the crack patterns are in good agreement with the experiments.

The validated model is used to investigate the OOP performance of pre-damaged walls, including both solid wall (without opening) and wall with an asymmetric opening. Two distinct approaches are considered to simulate the response of the pre-damaged walls. In the first approach, known as the reduced-parameters approach, a model is created with varying properties: reduced stiffness and strengths are assigned to locations where cracks were observed during the IP tests, while regular properties are maintained in other locations. Subsequently, the model is subjected to OOP analyses. In the second approach, known as the sequential loading approach, the wall is initially monotonically loaded in the IP direction that represents the pre-damage of the wall. Then, the OOP load is applied while maintaining the IP pre-deformation until the wall experiences failure. The study considers four different states of pre-damage, ranging from minor to extensive damage. For the solid wall, the damage levels are based on the observed damage during the IP tests up to the maximum drift of 0.2%. On the other hand, the damage levels for the wall with opening are derived from the damage observed during the IP monotonic pushover numerical simulation up to the maximum drift of 0.14%.

For the solid wall, it is found that both approaches give same results for low pre-applied IP damages, up to 0.06% drift. The reduction of the OOP peak strength is almost negligible until this drift level. As the damage increases, the reduction of the strength also sharply increases. At the maximum of 0.2% IP-drift, 40% reduction of the OOP peak strength of the wall is observed in the reduced-parameters approach, while in sequential loading approach, the wall immediately failed resulting in negligible OOP strength because of the severe IP damage. For the wall with opening, similar to the solid wall, no measurable influence of the OOP strength due to minor IP damages, up to 0.06% drift, could be observed in both approaches. The maximum reduction that could be observed is approximately 15% at maximum of 0.14% pre-applied IP drift. In the sequential loading approach, as the level of pre-damage is increased, the pre-peak stiffness of the force-displacement curve decreases, as expected for a pre-damaged wall. However, the reduced-parameters approach does not show this reduction, which could be attributed to the pre-damage applied only at specific locations. For both types of walls, there is no significant difference in the crack pattern of the undamaged and pre-damaged wall. The well-known envelope crack pattern is obtained in both cases.

To conclude, the out-of-plane load-bearing strength of URM walls is significantly affected by the presence of in-plane damages. The impact is minimal under minor in-plane damages but increases rapidly as the damage becomes more severe.

This thesis limits the numerical analyses to monotonic loading. However, for future research, it would be beneficial to extend the analyses to include cyclic or dynamic loads, as they provide a more realistic representation of seismic loading conditions. Moreover, it is recommended to incorporate various boundary conditions for the OOP loading. For instance, the research could be expanded to include a C-shaped wall configuration, where the lateral edges are supported by return walls, a scenario commonly encountered in practice.
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To stop the depletion of natural resources, reduce climate change and fight biodiversity loss a circular economy in 2050 is pursued. In the upcoming years a challenging opportunity arises. Many existing bridges and viaducts with bridge decks consisting of prefabricated concrete girders have to be replaced. These girders although not designed according to circularity concepts have potential to be reused in a new structure, which is in line with the highest achievable level of circularity. However, the construction market is not ready for this innovation. So, while current research still aims at the feasibility and suitability of the girders for reuse in new structures, this research aims at the next step of preparing the construction market. This is of high relevance because it speeds up the introduction process of the innovation and thereby safes girders from demolition.

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

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

In conclusion, this research provides the foundations for a changed design approach that is needed to prepare the construction market for reusing existing girders. By giving guidance to project teams, the view shifts from using new girders to reusing existing girders. This is valuable to reach the environmental objective of a circular economy in 2050.
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The development of an efficient and sustainable transportation system is crucial for the effective functioning of economies. Concrete, a widely used material for road construction, poses significant environmental challenges. A sustainable alternative is to use alkali-activated concrete (AAC) for road construction. However, the aggregates used in AAC are generally mined, contributing to the negative environmental impact. To address this concern, municipal solid waste incineration (MSWI) ashes, specifically MSWI bottom ash (BA), can be utilised to replace natural aggregates. Thus the construction of pavements using sustainable concrete facilitates its growing demand without burdening the environment.

This research focuses on the utilisation of municipal solid waste incineration bottom ash (MSWI BA) aggregates in AAC for potential application in pavements. The study was divided into five phases: aggregate characterisation, mechanical performance evaluation, long-term performance study, microstructure analysis, and life cycle assessment (LCA) analysis. The physical properties of MSWI BA aggregates indicated that the aggregates are porous and weak. Nonetheless, these aggregates showed comparable properties to natural aggregates and can still be used for pavement application. However, the metallic aluminium in the MSWI BA aggregates releases hydrogen gas leading to concrete cracking and swelling, thus, hindering its use in various applications. To address this concern, alkaline pre-treatment using sodium hydroxide solution was employed in this research. An optimal replacement level of 30% was chosen based on the effectiveness of the pre-treatment in removing metallic aluminium and the compressive strength of AAC containing MSWI BA aggregates.

In the next phase of the research, the mechanical and long-term performance of AAC with optimum replacement level was evaluated. The results demonstrated that the concrete satisfied the mechanical performance requirements for pavements. However, the freeze-thaw resistance of the AAC was below the norm requirement due to the air voids and associated cracking, which was confirmed through scanning electron microscopy (SEM) and X-ray computed tomography analysis.

SEM analysis revealed reactive phases in the MSWI BA aggregates and poor aggregate-matrix bonding for the coarser fraction compared to the finer aggregate fraction, leading to decreased mechanical performance. Despite these findings, the AAC containing MSWI BA aggregates satisfied the majority of the norm requirements, indicating its potential for road pavement application. However, evaluating the environmental impact of adding MSWI BA aggregates in concrete is essential. The life cycle assessment analysis demonstrated that the optimal MSWI BA sample exhibited better environmental effects, indicated by a lower environmental cost indicator value compared to AAC and ordinary Portland cement concrete samples with similar performance.

In conclusion, the pre-treatment method utilised in this research is optimal for a replacement level of 30% of gravel with MSWI BA aggregates. The AAC with 30% replacement level meets all the mechanical property requirements stipulated by the norm for pavement application, exhibits good air void distribution, and has limited environmental impact owing to the lower ECI value. This study evaluated the feasibility of applying MSWI BA aggregates in AAC for pavement application and showed promising results.
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On the 17th of October 2021, a concrete grandstand element collapsed at the Goffert stadium in the Netherlands after a crowd jumped on it for 8 seconds. An investigation by an engineering consultancy firm concluded that the design loads in the building code are too low, raising questions about the safety of grandstand elements. Currently, no method to assess the reliability of grandstand elements exists.

This thesis presents a state-of-the-art method to determine the reliability of concrete grandstand elements. The reliability is assessed by performing a non-linear dynamical analysis. The element is modelled as a non-linear single-degree-of-freedom system. Excitation signals are synthetically generated by consulting the literature and by analyzing a data set of jumping crowds. A bi-linear force- displacement relationship based on technical drawings of the collapsed grandstand element is adopted and extended by a model uncertainty parameter which accounts for both the non-linearity of the analysis and the uncertainty related to the dynamical basis of the analysis. The reliability is determined through a Monte Carlo simulation: almost 100,000 simulations can be performed per assessment.

Out of the 100,000 simulations, 0 failed. This result is not in line with what happened; one failed out of only a few elements. This gives rise to two different investigations. On the one hand, the failure of the Goffert stadium grandstand elements has to be explained. On the other hand, the lifetime reliability of a grandstand element has to be determined.

The first assessment indicated that if the element’s resistance conforms to the technical drawings, there is no cause for concern regarding its reliability. Measurements on 23 other grandstand elements in the same stadium showed a high variation in the concrete cover. The collapsed element was, therefore, also likely subjected to a high variation in the concrete cover. To understand the influence of an increased concrete cover on the reliability, two additional analyses were performed, where the post-yielding resistance of the structure was slightly reduced. This resulted in an increase in the probability of failure, which indicates that this parameter plays a crucial role in determining the reliability of grandstand elements. These points combined make it more plausible that the element failed because the concrete cover was larger than intended rather than the design loads being too low, as concluded by the engineering firm.

When investigating the lifetime reliability of grandstand elements in general, no collapse is expected after 8 seconds but rather after 30 seconds or even longer durations. Therefore, two additional analyses were performed where signals of longer durations (120 seconds and 300 seconds) excited the system. In these analyses, it is assumed that the resistance of the grandstand element conforms to the technical drawings. Signs of a converged reliability were perceived as 120- and 300-second excitation signals led to a probability of failure of the same order of magnitude, indicating that a steady-state solution is obtained after 120 seconds of jumping. In that case, the lifetime reliability of a grandstand element would be equal to the 120-second reliability. The corresponding reliability passes the lifetime reliability requirements for existing structures in consequence class 2 (for a reference period of 15 years).

While the results presented are estimations, and a larger sample size is needed for a converged probability of failure, the proposed method provides a valuable framework for assessing the reliability of grandstand elements. This method can easily be extended to any grandstand element by changing the model parameters, and the true reliability of grandstand elements can be assessed by performing more (1-10 million) simulations. ... Read more

Crownwalls are often placed on top of vertical composite breakwaters to reduce overtopping. Adding a seawards facing overhang at the top of crownwalls has successfully reduced overtopping even further without increasing the freeboard of the crownwall. Crownwalls with a fully curved (FC) face are most often used in seawalls where they are subjected to wave load by breaking waves. However, it has recently become of interest to explore the possibility of using the fully curved shape for vertical breakwater crownwalls instead of a crownwall with a recurve (R). This thesis aimed to investigate further the wave loading by non-breaking waves and the dynamic response of a FC crownwall on a vertical breakwater through an offline one-way coupling of a CFD-generated pressure-time series and a FEM model in Diana FEA. The results were then compared to those of other studies on the wave load and dynamic response of a R crownwall. Pressure-time series from CFD numerical simulations of three wave states (W5, W6 and W7) were analysed to determine how the structure was loaded. The analysis of the pressure-time series showed that for the smallest wave state, W5, the pressure distribution at the moment of maximum total force was trapezoidal. However, for the larger wave states, W6 and W7, there was a pressure peak at the top of the curve of the crownwall due to the C-CI phenomenon. Waves with impulsive pressure and force impacts were found in all wave states, and the pressure and force impulses were much less variable than the maximum pressure and force values. Dynamic nonlinear analysis showed the fully curved crownwall cracks under wave load by wave states 6 and 7. Cracking occurs at the centre of the curve, where the largest tensile stresses are located. Comparing the results to those of the recurved crownwall, it was concluded that the fully curved crownwall was less favourable than the recurved crownwall. For the same wave states, the FC crownwall was subjected to larger wave forces than the R crownwall, which led to a larger bending moment exerted on the structure. The FC crownwall is also larger than the R crownwall, with the same freeboard, and therefore requires more use of concrete. Due to the shape of the FC crownwall, the maximum tensile stresses are 2.5-3 times higher than those in the R crownwall. More use of steel reinforcement bars is therefore also needed. It would, however, be interesting to investigate further FC crownwalls on vertical breakwaters with different geometries, e.g. radius of the curve, to see if their design can be improved. The applicability of the extended Goda method for calculating static wave load on recurved crownwalls was also investigated for the FC crownwall. It was found that for waves with wave steepness less than 6% and vertical wave velocity less than 2.4 m/s, the calculation method could be used for a preliminary design. However, the dynamic response of the structure must be addressed in the final design, e.g. with a dynamic analysis or the DAF method. ... Read more