To prevent catastrophic structural failures, it is essential to monitor the condition of aging concrete structures and provide early warnings that enable timely mainte-nance and repair. Structural health monitoring (SHM) of concrete structures has attracted considerable attention in the research community. Among various SHM techniques, acoustic emission (AE) has emerged as a particularly effective method for early fracture detection, owing to its real-time monitoring capabilities and sen-sitivity to early crack formation.
However, a comprehensive review of the mechanisms and models related to AE phenomena in concrete fracture (Chapter 2) reveals ongoing challenges in applying AE reliably. A key difficulty lies in accurately correlating localized fracture events with AE signals recorded after wave propagation through complex structural media. Both experimental inversion and forward modelling approaches have been ex-plored to address this issue. Nevertheless, experimental techniques face inherent limitations due to complex wave propagation effects and sensor responses. Fur-thermore, existing modelling methods are not yet capable of explicitly simulating AE signals generated by concrete fracture.
This dissertation aims to investigate the source mechanisms underlying AE phe-nomena induced by concrete fracture and to establish a quantitative relationship between localized fracture events and the resulting AE signals. The overarching goal is to enhance the reliability of AE-based techniques for early warning applica-tions in concrete structures. Particular attention is given to AE signals generated by tensile cracking, which is the dominant source of AE activity, especially in the early stages of fracture when timely warnings are most critical. ... Read more

This dissertation investigates how proof load testing can be used to assess the reliability of existing structures. A flexible Bayesian methodology is proposed and applied to reinforced concrete road bridges and viaducts. Key contributions include:

• A demonstration of how proof load testing affects annual reliability, showing reductions during testing, but substantial gains after surviving target loads.

• An in-depth look at the conservative lower-bound estimation of structural reliability, revealing its assumptions and limitations.

• Combining in-situ monitoring and laboratory data for Bayesian updating during testing, enabling substantial reductions in required test loads.

• Hierarchical Bayesian modelling addressing spatial correlation and system reliability, enabling optimal testing strategies with a low number of tests, and the configuration of load testing vehicles.

This research positions proof load testing at the core of a Bayesian reliability-updating methodology, thereby providing a uniquely accurate procedure for assessing existing infrastructure. ... Read more

The building sector is a big sector that is very important for the global economy, but also has a big contribution to the greenhouse gas emission and production of construction waste. The building sector is responsible for about 37% of the global greenhouse gas emissions. In order to comply with the Paris Agreement on climate change, it is necessary to reduce the total emission of greenhouse gasses and the production of waste.
Modular construction is used for structural components, such as columns ,beams, and plates. However, it has not yet been implemented for shell structures. Shell structures are shape and material efficient, but often require unique formwork that is of one time usage, because of their complex geometries.
This research searches to improve the sustainability of shell structures by looking into the application of modular construction in this type of structures. With the use of the Goldberg-method a hexagon dominant pattern has been projected on a spherical dome structure. Creating a repeatable mesh pattern on the structural surface. Various segment sizes (N=4 till N=10) have been evaluated at the hand of a structural analysis in Grasshopper and Karamba3D. An uniform load, and a wind load have been used to obtain the stress distribution, displacement and buckling load factors for the different segment sizes.
It was found that smaller segments result in a more efficient force distribution, but larger segments have a lower labour intensity. From the analysis the optimal situation has been found at N=8, giving a balanced result between structural performance and labour intensity. With situation the difference in performance for different boundary conditions, and joint stiffness has been investigated. Here it was found that the segmentation of the shell lowers the buckling stability of a structure, but that modular construction is possible with different boundary conditions and even with the introduction of an oculus.
From the optimal situation N=8, 20 modules can be extracted. With the use of k-means clustering on the edges off the different modules, these modules can be further optimised. This leads to a adjusted set of 16 modules, with only 6 different module edges. The optimised modules have a higher potential for more configurations.
The results show that modular construction is possible within shell structures without compromising the structural integrity. It also results in a set of modules that can potentially be used in different configura-tions and across different structures. With this the research contributes to a more sustainable and circu-lar construction approach for shell structures.
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This thesis investigates the impact of confinement on the structural performance of Concrete-Filled Steel Pipe (CFSP) pile to concrete cap connections in the absence of dedicated force transfer provisions such as dowels or shear rings. Current Eurocode guidelines provide no explicit framework for confinement in partially loaded areas, resulting in uncertainties in design. The research combines theoretical modelling, drawing on Mander’s confined concrete model and the Dual–Wedge Stress Field (DWSF) approach of Markič et al., with a finite element case study to evaluate confinement mechanisms. A quasi-non-linear analysis was implemented to approximate peak concrete strength, supported by analytical formulations and parametric scripts. The findings confirm that confinement significantly enhances bearing capacity and stress transfer in CFSP pile–to–cap connections, with the FEA substantiating several features of the DWSF model while also highlighting limitations in reinforcement activation and stress redistribution. Overall, the study demonstrates that confinement effects are decisive for structural performance and should be explicitly considered in design practice to achieve reliable and efficient CFSP connections.
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Due to aging, increase in service loads, and/or upgrade of design codes, many existing concrete structures do not, or soon will not satisfy the required load-bearing capacity. Therefore, measures such as reconstruction or repair are necessary. Among various strengthening methods, ultra-high performance fiber reinforced concrete (UHPFRC), due to its high mechanical properties and superior durability, has emerged as a promising solution for strengthening concrete structures by enhancing load and deformation capacity, and improving durability. While extensive research has been conducted on the use of UHPFRC for flexural strengthening, studies focused on shear strengthening remain limited. After strengthening, the interface between UHPFRC and traditional reinforced concrete (RC) structures is formed. However, interface behavior has not been thoroughly investigated, further posing a gap in understanding the optimal strengthening design of UHPFRC in hybrid UHPFRC-concrete systems.

This dissertation focuses on the shear performance of concrete structures strengthened with UHPFRC, with a focus on the interface behavior between UHPFRC and normal concrete, and the mechanical properties of UHPFRC.

To assess the shear strengthening efficiency of UHPFRC, this dissertation starts with a literature review (Chapter 2) that addresses three major aspects. The first aspect focuses on the shear performance of hybrid UHPFRC-RC structures. Strengthening applications of UHPFRC in shear, and current analytical and numerical methods to predict the shear capacity of RC structures strengthened with UHPFRC are critically analyzed. The second aspect is focused on the UHPFRC-concrete interface behavior which is governing the response of the hybrid beams. From the review, the role of governing parameters on the interface behavior, including the effects of bonding technique, moisture exchange between the two materials, differential shrinkage and the role of coupled environmental and mechanical loads, are discussed. The final aspect deals with the application of non-destructive techniques (NDTs) to assess the strengthening efficiency of UHPFRC, focusing on evaluation of (i) UHPFRC material properties and (ii) UHPFRC-concrete interface performance in hybrid structures.

Experimental design is presented in Chapter 3, where the material and structural tests are systematically introduced. This chapter provides a series of material tests to, among others, characterize the workability, shrinkage and mechanical properties of both UHPFRC and normal concrete (NC). It also introduces the design and setup of a comprehensive structural test to evaluate the shear performance of UHPFRC-strengthened RC beams. Following the experimental methodology from Chapter 3, Chapter 4 presents the results of the material and structural tests. Through comparative analysis, this chapter examines the material and structural behavior of UHPFRC-strengthened beams and its constituents by varying different parameters, thereby setting a basis for evaluating the shear improvement in strengthened RC beams. In order to provide a deeper analysis on the UHPFRC-concrete interface quality in strengthened beams, Chapter 5 focuses on the assessment of possible delamination between UHPFRC and existing concrete by applying active infrared thermography. Combined with both experimental and numerical analysis, a systematic procedure is developed to detect subsurface delamination in hybrid UHPFRC-NC specimens. Besides the interface properties, another governing parameter, namely the material properties of UHPFRC, is examined in Chapter 6. This chapter investigates the fiber distribution and orientation within UHPFRC elements, important factors influencing material properties of UHPFRC, and therefore further affecting its shear strengthening efficiency. Using a calibrated electromagnetic method and validated through x-ray computed tomography (CT scanning), the effect of governing parameters, including casting direction and vibration time, on fiber distribution and orientation in UHPFRC elements is investigated. This chapter helps to clarify the connection between the material properties of UHPFRC and its structural performance.

Based on the structural test results (Chapter 4), evaluation of interface properties (Chapter 5) and material properties of UHPFRC (Chapter 6), in Chapter 7, a numerical model is developed to simulate shear performance of UHPFRC strengthened concrete structures, validated by the experimental results. A parametric study is further conducted to investigate key factors including interface properties, UHPFRC tensile behavior and non-uniform fiber distribution in UHPFRC. The numerical analysis offers insights on the influence of these parameters on shear strengthening efficiency.

In the final Chapter 8, the findings regarding the overall shear strengthening performance of UHPFRC in RC beams are given, providing practical insights for optimizing UHPFRC applications in concrete structures. Finally, suggestions for future research are given. ... Read more

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

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

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

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

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

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

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

Concrete is the second most used material in the world after water and recent trends show no slowing down of the concrete use around the world. Concrete is also a huge contributor to CO2 emissions as it makes up 8% of emissions. This study investigates the optimization of concrete structures to reduce environmental impact while maintaining structural integrity and cost-effectiveness, e.g. how to make a concrete structure more sustainable. A previous report where quay wall designs of different materials were compared in regard to the CO2-emissions and life cycle assessment found that a concrete quay wall had 43% more emissions than a steel quay wall. The goal of this study is to reduce the overall CO2 equivalent emissions related to a concrete structure by 50% and make the design more sustainable.
A concrete ship lock chamber as part of the Delta21 project is used as a case study. To measure the positive effect of sustainability two chambers are designed; a base case chamber designed based on what is most commonly done in practice in the structural engineering field, and an alternative chamber design with the aim of making the concrete lock chamber more sustainable. A partial life cycle assessment (LCA) is performed on both of the two design alternatives. The optimization of the alternative chamber design focused on minimizing global warming potential (GWP) by adjusting the reinforcement-to-concrete ratio and incorporating structural elements such as plated steel anchors. The two alternatives are analysed comparably as they are designed under the exact same conditions, in the same environment and with the same functionality aspects.
The base case structure is a U-basin concrete chamber with tapered walls. The alternative optimised structure enhances the structural behaviour of the chamber wall by adding anchors. This reduces the moments by 88% and the shear force by 56% compared to the base case design. By changing the structural wall type in the chamber by adding anchors, the concrete volume could be reduced by 47% between the base case design and the optimised design. This also allows for a reduction of concrete strength class, reinforcement volume, underwater concrete floor thickness and the number of tension piles for the construction pit. The LCA reveals a 55% reduction in the GWP for the alternative concrete chamber design, compared to the base case design. An optimum reinforcement ratio for the alternative concrete chamber anchored wall of 2.3% is identified, resulting in a balance between structural performance and environmental sustainability without increasing material costs. This ratio doesn’t incorporate labour cost which might affect this optimum ratio by lowering it. This demonstrates the potential for achieving environmentally responsible solutions without compromising the structural integrity of a structure or incurring additional costs.
The study highlights the potential for integrating sustainability objectives into concrete structure design, with recommendations for further research including exploring alternative materials and advanced optimization techniques. ... Read more

The offshore renewable energy market is rapidly growing, particularly in wind and solar sectors. The intermittent nature of these energy sources underscores the necessity for offshore energy storage solutions. Among the techniques being explored, Marine Pumped Hydro-Energy Storage (MPHES) emerges as a promising option. This innovative concept operates similarly to artificial lakes, where water is stored and released to generate electricity. In the MPHES system, a seabed-based reservoir is established, in which water flows, driving turbines to generate electricity. During periods of energy surplus, the system is charged by pumping water out of the reservoir... ... Read more

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

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

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

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

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

he growing demand for renewable energy sources has led to the deployment of wind turbines worldwide. One of the most critical parts of a wind turbine is the foundation, which plays an important role in maintaining the structural integrity and reliability of the towers throughout their service life. This research project is a case study that focuses on validating the numerical model against the experimental values from an operational onshore wind turbine foundation present at Riemst, Belgium, while considering the effect of hydration heat during the concrete curing process. The main aim of this research is to study and compare the behavior of the steel stresses in the on-site foundation with that of the numerical analysis and to see whether an adequate match can be obtained.

The study begins with the development of a three-dimensional symmetrical finite element model that captures its intricate geometrical and material properties. The structure’s behavior is simulated under realistic loading conditions to assess its structural performance and identify potential areas of concern. To validate the accuracy of the numerical analysis, experimental data obtained from fiber optic sensors are used. After converting the measured strains into stresses, they are carefully compared with the finite element analysis results to identify any variations and fine-tune the model. The validation of the FE model is performed using a 2D plate model in SCIA Engineering.

The research investigates the effects of hydration heat along with the structural analysis in FEA on the stresses experienced by the steel elements in the mass structure. This further extends to the effects of bedding and inclined piles combined with the thermo-mechanical analysis, where properties such as stiffness are varied in the simulations to study their influence on the structural response. It is imperative to note that utilizing the FE model with solely non-linear structural analysis can lead to a significant overestimation of the expected field results, up to 87 times. To mitigate this issue, the variant with thermo-mechanical analysis is implemented, reducing this estimation to a maximum factor of 58 compared to the field data.

It is crucial to achieve a satisfactory level of the project through iterative modifications. Implementing soil bedding on all sides in the thermo-mechanical model is one such step to effectively reduce steel stress to an acceptable level. The model shows steel stresses that are approximately 26 times higher than the actual experimental values. Along with reducing the steel stresses, the crack widths have decreased considerably from 3.4 mm to 2.35 mm. Hence, the effective way to perform the numerical simulation is to consider thermo-mechanical coupling along with minimizing assumptions and ensuring sufficient stiffness of the structure for reliable assessments of steel stresses and structural integrity of onshore wind turbine foundations.

The findings contribute valuable insights into the foundation’s structural behavior under varying operational conditions, highlighting areas of strength and potential advancement. Moreover, the outcomes from this investigation can assist engineers and designers in making informed decisions during the planning and construction phases of wind turbine foundations, leading to more cost-effective and robust structures. Additionally, the methodologies presented here may serve as a framework for future research in this field. ... Read more

Across the Netherlands close to 70 prestressed concrete T-beam bridges with cast-in-between slabs and transverse prestressing built in the 60's and are still in service. The current code NEN-EN 1992-1-1+C2:2011 assesses the shear capacity more conservatively. In addition, the NEN-EN 1991-2+C1:2015 prescribes an increased traffic load. This results in this type of bridge not complying with the current codes and the shear capacities are considered insufficient. However, upon inspection these bridges do not show signs of distress. This suggests the presence of additional load-carrying capacity, which is not considered in the current Eurocode.

Non-linear finite element analysis (NLFEA) can be used to accurately approximate the structural behaviour. This includes yielding of steel, cracking and crushing of concrete, the development of alternative load paths as well as snap-back and snap-through behaviour. However, performing each load step requires a great amount of computational effort depending on the amount of degrees of freedom of the model. In FEA a continuous shape is divided into discrete elements which together form a mesh. These meshes can be volumes, surfaces or lines.

To describe the geometry of the prestressed concrete T-beam bridges with cast-in-between slabs either volume elements or multiple surface meshes in different planes are required. Using a mesh of solids would result in system with such a high number of degrees of freedom which might even exceed the available computational capabilities or result in a very long duration of the analysis at best. Using shell elements to construct the mesh reduces the number of degrees of freedom by at least two thirds.

In this thesis I investigate to which extent we can simulate the structural behaviour of a prestressed T-beam slab bridge deck using a non-linear finite element model with a 3D non-planar mesh of shell elements. The Vechtbrug bridge near Muiden was a bridge of this type. A team of researchers from TU Delft have performed several collapse tests on this bridge. This includes extensive measurements of all the experiments as well as material testing on concrete and steel samples. For my own research, a single case study is conducted by recreating collapse tests performed on the Vechtbrug in which both isolated beams and unmodified spans have been loaded past failure. The results of the material tests provide accurate material properties as input for my numerical models. The results of the collapse tests allow for verification and validation of the outcome of the performed finite element analyses.\\

The results of the numerical analyses show a close approximation of the true collapse load with an overestimation of 15\% for the isolated beam model and 12\% for the cooperative beams model. The deflection again is overestimated with 18 and 56\%. The deflection of the adjacent beams relative to the loaded beam is too low. The numerical model is underestimating the transverse load distribution by $\pm$ 25\% for the adjacent beams and $\pm$ 34\% for the beams adjacent to those. The Guyon Massonnet method was applied to estimate the transverse load distribution with the supplied material properties and including the two cross beams. By contrast, the results were an overestimation of approximately 70% for the immediate adjacent beams. In the third numerical analysis the complete bridge deck and ultimate limit state verification is performed by applying the prescribed traffic load with all safety factors applied. The bridge can withstand 234\% of the prescribed load which agrees with the lack of damage present on the Vechtbrug after experiencing over 50 years of traffic load.

The results show that a non-planar shell mesh can generate a realistic structural response considering the collapse load approximates the actual one found in the collapse tests. However, this is somewhat limited for decks consisting of multiple beams since the implementation of the transverse load distribution in the numerical model was inaccurate. The structural response of the structure was too ductile in the numerical analysis with the deflection being overestimated and the strain under the loading plate double the value of the collapse test. Both Mustafa and Ensink have performed a numerical analysis of the isolated beam model using a mesh of solid elements prior to my thesis work. The results of the isolated beam model match closely in both the results of the NLFEA performed by Mustafa and Ensink. The solid mesh does yield more realistic cracking patterns. The isolated beam model showed the required evidence to demonstrate the activation of arching action: An increase in the horizontal reaction force required to lateral restrain the beam with the bending crack occurring under the loading plate so the arch action phenomenon could be activated. In the complete deck model evidence of compressive membrane action in the transverse direction was detected. In both the complete deck models, evidence of lateral confinement was demonstrated, increasing the maximum compressive stress of the concrete.

Finally we can conclude that a NLFEA with a 3D non-planar mesh of shell elements yields accurate results when considering a single strip of the bridge deck. However, the model with a the mesh representing the complete bridge deck, the capacity of the transverse load distribution is underestimated and the structure shows overly ductile behaviour. The model is capable of including the load-carrying mechanisms arch-action, compressive membrane action and fixed boundary action as well as the effect of lateral confinement. ... Read more

This thesis explores a suitable method and appropriate input to determine the failure probability of thermal shrinkage cracking in a steel fibre-reinforced underwater concrete floor by examining the factors that influence this failure probability.

An underwater concrete (UWC) floor is a common construction type in the Netherlands that is often applied to create building pits under the groundwater table. Usually, these (generally unreinforced) UWC floors only function as a watertight bottom layer of the building pit with only a temporary sealing function. Water tightness and crack prevention are very important aspects of this type of construction. A permanent reinforced structural top floor is frequently used on top of the temporary UWC floor to make a completely watertight construction, which is not the most sustainable and cost-efficient solution. Advances in concrete technology such as fibre-reinforced concrete have made it possible to integrate both the UWC and structural top floor or even use the UWC floor as the permanent structural floor. In these cases, the UWC floor should already function as a watertight barrier and controlling leakage by limiting the crack width becomes even more important. The addition of fibres to concrete may prevent through crack formation in the UWC slab and the possible consequent leakage. An important cause of cracking in UWC floors is thermal shrinkage during the cooling phase of the hardening reaction shortly after casting the UWC floor.

Currently, there are no guidelines for the construction of fibre-reinforced concrete (FRC) floors and the prevention or limitation of thermal shrinkage cracking. A CROW-committee "Steel fibre reinforced underwater concrete (SFRUWC) floor as permanent structural floor" has been formed. This committee aims to set up a design recommendation and part of that is addressing the thermal shrinkage cracking problem. There is a lot of uncertainty in geometry, material properties and boundary conditions associated with SFRUWC floor design and construction. Because of this, there is a need for a probabilistic approach to investigate the influence of these uncertainties and tolerances on crack formation in SFRUWC floors during the hardening phase. This research aims to determine a suitable probabilistic method to investigate the failure probability of SFRUWC floors and the parameters that influence this.

In order to achieve this, a finite element model was developed that determines the shrinkage cracking behaviour in a part of a UWC floor in a building pit. Before this model could be developed, all the necessary input parameters and design equations were collected from literature and existing guidelines. To set up a model, first the behaviour of UWC floors was studied, followed by the development of a finite element model that includes the hardening behaviour and strength development of young concrete. An important aspect of this finite element model is the use of random fields to introduce spatial variation in the strength properties of the SFRUWC floor, which is a first step to include stochastic variation in the model for the probabilistic analysis. A probabilistic sensitivity study was performed with the finite element model by calculating multiple samples for each set of input parameters. Separate input parameters were varied and the influence on the results was investigated. The parameters that were considered, include the random field properties, material properties and thermal properties. Finally, a full Monte Carlo analysis was performed to give a proof of concept on how to calculate the failure probability regarding thermal shrinkage cracking in SFRUWC floors.

In order to prevent leaking cracks and satisfy the crack width criterion, the tension-hardening behaviour of FRC has to be utilised. Tension hardening behaviour will lead to a distributed cracking pattern, consisting of multiple small cracks which can satisfy the crack width criterion as opposed to a single large separation crack which does not satisfy the maximum allowable crack width criterion. It was found that the tensile behaviour of FRC and the use of random fields to model this tensile behaviour were major parameters that influenced the crack width and the occurrence of a distributed crack pattern. An important parameter is the standard deviation of the random field, which influences the difference between the maximum and minimum tensile strength in different locations in the slab. Looking at material behaviour, the main conclusion was that the introduction of a small hardening branch in the tensile material model was the governing influence factor. Both the standard deviation of the random field and the introduction of a hardening branch in the tensile behaviour affect the ratio between the tensile strength of the ordinary concrete and the residual tensile strength of the fibre-reinforced concrete. These two factors in combination with the model that was used, turned out to be dominating the results in such a way that the other input parameters only had a relatively small influence on the crack widths.

To determine maximum crack widths in SFRUWC floor it is essential to consider multiple samples with different random fields to find out if only a distributed crack pattern is possible or whether also single localised cracks can occur. The possibility of both these results being able to occur, leads to a large possible error in the maximum crack width. The results of this thesis have shown that the random field parameters remain uncertain and experimental research is needed to determine these correctly. Until then, it is important to investigate how significantly these parameters influence the results. It is recommended to extend this research by improving the model by making it more realistic and finding out if these two factors are still the dominating input parameters.
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Port of Rotterdam has the ambition to reduce the footprint for building new quay walls, this is in line with their ambition to reduce the footprint and with national goals to limit global warming. The aim is to use less materials and/or use different design solutions. These reinforced structures are designed in a conventional way and the internal forces are determined by performing a Linear Elastic Analysis. The reinforcement is calculated using the internal forces and is based on the Eurocode 1992 -1-1. The conventional approach includes various assumptions that affect the amount of concrete and steel used, which influences the CO2 footprint, structure reliability, and costs. In order to know the effects of these assumptions, advanced nonlinear calculations are carried out using volume elements ... Read more

In the construction of subsoil structures, a common challenge is the presence of a high groundwater level in combination with the absence of a naturally impermeable layer or an environment susceptible to settlements due to lowering the groundwater level. To overcome this issue, a building pit with an underwater concrete floor (UCF) can be constructed. The UCF ensures structural rigidity and allows for the building pit to be drained such that a dry and safe subsoil construction site is obtained.

The objective of this thesis is to investigate how design efficiency of underwater concrete floors can be improved. In an effort to reduce material usage and achieve cost-effective structures, the following research question was stated:

“What is the influence of design parameters and how can parameters be adjusted to improve design efficiency of an underwater concrete floor, and to what extent can the addition of fibre reinforcement contribute to this optimization?”

A parametric model was developed to provide insight to the sensitivity of parameters and their impact on design resistance. Furthermore, the model was utilized to examine under what circumstances potential material savings can be obtained by implementing fibre reinforced concrete in UCF’s. This was accomplished through the evaluation and comparison of the minimum required thickness based on bending moment resistance in various scenarios, for both UCF’s and steel fibre reinforced UCF’s (SFUCF).

Results obtained with the parametric model established that, in order to enhance the bending moment resistance of an uncracked UCF, increasing the nominal thickness becomes relatively more effective compared to increasing the concrete strength class for higher normal forces. When utilizing a compression arch to obtain bending moment resistance, the implementation of ribbed tensile elements or an increase in nominal thickness are found to be the most suitable methods for increasing resistance. For enhanced shear force resistance, increasing the nominal thickness over the concrete class provides relatively more additional resistance for slender UCF’s. The results found that through the application of ribbed piles, most punching shear force resistance can be obtained.

Three use cases for a SFUCF were identified using the parametric model. When centre to centre (c.t.c.) distances larger than 4.4m are applied in combination with a substantial normal force, significant material savings of up to 0.3m thickness are possible, which equates to a reduction of material usage by 30%. For situations where the effective height of the compression arch is small, it was also found that material usage could be reduced by 30%. Perhaps the most significant use case for a SFUCF is when the normal force is close to zero, and additional normal force cannot be obtained through membrane action. In these situations, the application of a SFUCF can make an otherwise near impossible project feasible.

As a new design approach, a cost-based optimization tool was developed using the parametric model. An already executed UCF was evaluated using the tool, it was determined that a more cost-effective design could have been achieved, with potential savings of up to 30% in costs.
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A significant part of composite concrete viaducts was built in the 50s and 60s. This has led to an increasing need for the reassessment of the precast concrete beam bridges in the Netherlands. Many of those bridges are nowadays subjected to higher traffic loads and consequently, have a certain risk of not complying with the currently used design codes. As a result, there is a demand for the development of nonlinear finite element solution strategies, which would increase the reliability of the numerical methods in safety assessment. In this research, special consideration is given to the precast, prestressed beam bridges which were made continuous by applying cast-in-situ cross beams and a top layer above the supports. In such structures, the hogging bending moment introduces more complex stress conditions in the concrete parts and more specific at the interface between precast girders and the top slab, compared to simply supported beam bridges.
Thus, one of the key aspects of the structural performance of composite bridges is the interfacial behaviour. The focus of this research is to study the stress conditions in the vicinity and at the interface and explore methods of numerical modelling of the interface in concrete-to-concrete connections between precast beams and top layers to initiate the development of modelling strategies for this type of interfaces.
The literature review was focused on prefabricated beam bridges, the current state of knowledge on concrete-to-concrete interfaces, along with design recommendations and past experimental and numerical research. Moreover, available interface element types, material models and modelling guidelines were explored. Since DIANA FEA is used within the course of this research, the study of the available models was limited to the ones provided by this software. It was noted that the Linear Elasticity model is the simplest way of interface modelling, therefore it was utilised in the initial stage of the research. More advanced models, Coulomb Friction and Combined Cracking-Shearing-Crushing, were considered worth investigating owing to accounting for coupling between normal and tangential behaviour. The Nonlinear Elasticity material model was also recognized due to the introduction of nonlinear effects, yet being relatively simple to assemble.
The initial phase of the research was a linear, phased analysis of the continuous, composite, concrete girder. Three models were tested within this part of the research – the model without interface elements, and two with linear elastic interface elements, one having high, penalty stiffness and the other having lower, more realistic value of shear stiffness. It was verified that the models without and with penalty stiffness interface performed almost equally. The decrease in stiffness and the deterioration of the composite action caused by this, resulted in an increase of stresses in the precast element. By the support, the extreme tension raised by a factor of 1.21 and under the point of load application the compressive stresses in the beams’ web elevated by 2.26. Based on the linear analysis, no significant tensile stresses perpendicular to the interface were detected. According to the analysis of interfacial stresses interaction and assumed failure envelopes, at four chosen points - above the support, at midspan of the main span, at the local shear extreme and under the point of load application - it was observed that the point above the support is not at risk of failure, whereas the point in the midspan might be. It was concluded that the combination of stresses is relevant not only because of a possible decrease in capacity due to tension but also increase under compression. As a result, models accounting for coupling between normal and shear tractions and relative displacements are worth investigating. It was also observed, that cracking in concrete elements by the support is expected, hence nonlinear analysis is required.
The component-level experiments found in the literature were analysed in the following section to be able to perform verification study of Coulomb Friction (CF) and Combined Cracking-Shearing-Crushing (CCSC) interface material models. Based on single element FE tests it was concluded that both material models proved to be well-suited for capturing the shear-normal stresses coupling. With the same input parameters, but higher normal pressure, the shear capacity increased, representing well the reference data. The CCSC interface material model’s ability to capture both cohesion and friction softening, was also verified with the single element models. Moreover, tension softening based on mode I fracture energy can be accounted for in that material model, as well as the fracture energy’s and dilatancy’s dependency on confining stress. However, those parameters were not verified, due to, among others, limited experimental data. Element assembly with the CCSC material model for the interface, circular beam bond-slip reinforcement and nonlinear material properties of concrete, was used to analyse the specimens with rebars crossing the interface. This approach, was assumed to represent the force transfer mechanisms to the highest extent, since cohesion and friction, generated by both external pressure and reinforcing bars, along with their softening, as well as dowel action, can theoretically be represented by such model. It was observed that this type of strategy resulted in convergence issues, and due to large number of input parameters it is quite complex to analyse or further calibrate. However, the approach seemed promising since the peak loads were underestimated by only 7-15% with respect to the mean, experimentally obtained values.
In the final Chapter the Combined Cracking-Shearing-Crushing (CCSC) interface material model, with bond-slip beam reinforcements was applied in the nonlinear analysis of the previously analysed composite girder. As an alternative, the model with the Nonlinear Elasticity(NE) interface material model was also constructed, based on the analogous input parameters, to be able to compare the modelling methods. In total four models were analysed, since two sets of input, one based on Eurocode 2 and the other on best guess stemming from literature findings, were studied. What was found to be promising is that the global behaviour, assessed on the basis of crack patterns, of the beams with corresponding input, was quite similar for the analyses with the CCSC and the NE material models. With the applied numerical setup, it was not possible to obtain the total load-displacement path of the composite beams using the CCSC material model for the interface, since the models diverged. The NE material model performed more stable and allowed for the analyses to continue, which is its main advantage. Another benefit is the ease of assembly, in comparison with the CCSC model. Nevertheless, it was demonstrated that the NE might provide overestimated results due to not considering the interaction of tractions. It was highlighted that the models’ validation with experiments is needed to recommend one of the models or either of the input sets. It was recommended to simplify the approach with the CCSC material model, by for instance, simplifying the numerical setup of interface reinforcement. Moreover, according to the literature findings the scatter of cohesion and friction coefficients, as well as other input parameters, is still quite large, thus experimental research in the form of push-off tests focused on those, particular interfaces is recommended. ... Read more

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...

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In the energy sector, a transition is made from fossil fuels to sustainable energies. Due to an irregular supply of these sustainable energies, it often occurs that there is a mismatch between supply and demand. Energy storage is a promising technique to overcome this. In this thesis, the aim is to store gravitational energy in concrete spheres which are placed on the seabed.

Therefore, this thesis aims to answer whether the most optimal construction method uses 3D Concrete Printing (3DCP) and if so, what the optimal construction method will be using 3DCP. Based on a specific case, five main construction methods are qualitative investigated, from which two are with 3DCP. From an evaluation, it followed that a combination of 3DCP and conventional casting is the most promising method and is therefore selected for more in-depth research. In this construction method, the formwork is made with 3DCP and concrete is cast in the formwork. A prefab bottom and top part are required, because the maximum inclination (nowadays) for printing is limited to 45°.

Based on the selected construction method, three different 3DCP-variants are investigated: construction in the dry (1), submerged construction (2) and construction on a pontoon (3). The two main topics that are investigated are the use of 3DCP for the formwork and the suitability of unreinforced concrete for the sphere itself. The possible use of 3DCP is verified based on two failure mechanisms: plastic collapse (results in minimal free height of the formwork) and elastic collapse (results in maximum free height of the formwork). The suitability of unreinforced concrete is verified based on strength requirements.

Both in case of construction in the dry and construction on a pontoon, h1 is 0.20 m and h2 is 0.65 m. In case of submerged construction, h1 is 0.25 m and h2 is 0.72 m. The unreinforced wall thickness should not exceed 2.5 m because it is required that the sphere is buoyant. For this wall thickness, a concrete strength class of C60/75 is required for construction in the dry, submerged construction and construction on a pontoon. An evaluation based on feasibility and reliability, combined with the results above, shows that construction in the dry is the most promising method.

An adiabatic calculation is made of the temperature increase of the concrete, based on five different cement compositions. It followed that unreinforced concrete will crack. However, in reality, the temperature increase is semi-adiabatic, resulting in lower tensile stresses. It is therefore highly recommended to further investigate this temperature increase in order to verify the suitability of unreinforced concrete. Measures that could be taken to lower the temperature differences are: addition of liquid nitrogen or addition of ice instead of water for the concrete mix. Besides that, it is recommended to investigate the possible use of fibre-reinforced concrete, which could significantly increase the tensile strength of concrete.
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The light and frequent earthquakes in the north of the Netherlands, particularly in the province of Groningen, have recently exposed the unreinforced masonry structures to seismic activities. Since these structures do not adhere to seismic regulations, they are considered vulnerable to seismicity. The ultimate state capacity of the structures is important for an individual's safety, however, these earthquakes are of low intensity and cause aesthetic damage.

In order to investigate the light damage initiation and development, TNO has performed shaking table tests on an unreinforced masonry (URM) cavity wall specimen in out-of-plane (OOP) one-way bending with small increments in intensity. The test specimen consisted of calcium silicate brick inner leaf and perforated clay brick outer leaf. The damage development in the outer leaf was monitored during these tests using a high-speed digital image correlation (DIC) technique to study the initiation and development of damage in the outer leaf of the specimen. The experimental tests showed damage initiation at the mid-height of the outer leaf. The tests could not capture the development of cracks through the thickness of the cavity wall.

The scope of this research is a numerical assessment of the experimental study by using a Non-Linear Time History (NLTH) analysis of light damage initiation and development of a URM cavity wall under out-of-plane loading. The high-resolution experimental results are used as a basis for the development and calibration of models which can better predict the crack initiation and development in URM. The finite element software DIANA 10.5 FEA was used to set up the numerical model and conduct transient analysis.

The seismic signal as an input loading and the top boundary condition of the test specimen. The acceleration data measured from the shaking table tests at the base was used as an input seismic signal for the transient analysis of the models. The input signal needed to be processed before application as the presence of low-frequency content leaded to inaccurate results. Different approaches are discussed in this thesis regarding the processing of the input acceleration signal.

The experimental tests were modeled along the cross-section of the test specimen, thereby highlighting the thickness of the inner leaf and the outer leaf. This enabled tracking the light damage initiation and propagation through the thickness of the cavity wall. A total of thirteen shaking table tests were conducted on the experimental setup. In order to gain insight into the behavior of the specimen during each shaking table test, a model was created corresponding to each shaking table test. Preliminary analysis schemes were set in order to check the validity of all thirteen models. The two cases of top boundary conditions were checked, roller support and spring-mass support. The roller boundary condition proved to be stiff in comparison to the experimental results.

The numerical results were calibrated on the basis of material properties. The results were compared to experimental results by checking the dynamic behavior at the mid-height, dynamic behavior over the height, and light damage initiation and development of the specimen. The results of the numerical models were stiff in comparison to the experimental results. According to the conclusions, it is recommended to research further regarding the boundary conditions, especially the bottom boundary condition due to the formation of a rocking crack. Another important aspect to focus on is the combination of all input signals, thereby, taking into consideration the damage accumulation. ... Read more

The construction sector plays a significant role in the environment, and concrete structures constitute a substantial portion of this sector. The government is actively seeking ways to reduce the environmental impact of construction activities by promoting a more sustainable approach. In the Netherlands, a considerable number of repetitive cellular residential buildings are constructed using the tunnel formwork building method. Although this method can be enhanced in terms of sustainability by utilizing environmentally friendly cement mixtures, it poses challenges, such as an increase in execution time. This research aims to explore a more sustainable approach to the tunnel formwork building method while devising strategies to maintain the same execution time as before.

The tunnel formwork building method operates with a 24-hour daily execution cycle. During the initial 8 hours, the formwork, reinforcement, and installations are set up, followed by pouring concrete at the end of the day. After 16 hours, the concrete attains sufficient strength for the formwork to be dismantled, allowing it to be placed on the next grid. This approach results in rapid construction, high-quality output, and cost-effectiveness. However, a significant drawback is the reliance on CEM I mixtures, which consist of approximately 100\% Portland cement, contributing to substantial greenhouse gas emissions and environmental impact. Blended cement mixtures, such as CEM II and CEM III, offer more environmentally friendly alternatives by incorporating lower percentages of Portland cement blended with fly ash or blast furnace slag. Despite their environmental benefits, these mixtures exhibit a slower strength development, making it challenging to achieve a hardening time of 16 hours.

In pursuit of a dependable and sustainable approach to the tunnel formwork building method that preserves the 24-hour daily cycle, the research question is articulated as follows: "What concrete mixtures and execution strategies can be applied in the Netherlands to diminish the environmental impact of the traditional tunnel formwork building method, utilizing sustainable cement mixtures, while upholding existing advantages in time, cost, and quality?" This research question will guide the exploration of optimal concrete mixtures and execution measures for implementing sustainable cement mixtures within the tunnel formwork building method, while ensuring the continuity of the daily execution cycle.

In addressing this research question, an Excel calculation sheet has been developed. This sheet serves to compute the material costs, shadow costs, and formwork removal time associated with specific modifications in the design, concrete mixture, and additional execution measures for the tunnel formwork building method. The calculation sheet offers flexibility with three grid sizes: 4.5m, 6.0m, and 7.2m. It incorporates various concrete properties, such as the cement mixture (CEM I, CEM II, or CEM III), w/c ratio (0.45 or 0.55), aggregate types (fine and coarse), Blaine value (300 or 400$m^2/kg$), and admixtures (basic and additional). Additionally, the calculation sheet allows for adjustments in seasonal conditions, with options for summer (20°C) or winter (10°C)... ... Read more