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

Currently a new Eurocode is in development where the shear capacity will be based on the Critical Shear Crack Theory (CSCT), rather than a purely empirical model. The newly introduced formulae provide good results overall and include the effects of bending moments on the shear capacity. However, the formulae are known to be too conservative for prestressed continuous beams with low amounts of shear reinforcement and severely underestimate the shear capacity. If these formulae are applied, many existing structures would therefore no longer meet the code requirements. New structures with prestressed continuous elements would also require more material and it may become difficult to design efficient concrete members that meet the new code requirements.
To prevent substantial costs, emissions and time investments, it was questioned if the design capacity of prestressed beams near intermediate supports could be increased by changing the location of the control section from 1d away from supports to the critical cross section. The location of the control cross section greatly influences the shear resistance according to the CSCT calculation. However, it is unclear how the critical cross section can be determined accurately.
In this thesis the location of the critical cross section near intermediate supports was investigated for prestressed continuous beams with less than the minimum required shear reinforcement. A small number of models and experiments from literature were compared. Additionally, multiple Finite Element Analyses have been performed with a variety of settings, assuming different shear behaviour. A plasticity approach was also investigated, where the critical cross section is found at the location where the cracking load equals the ultimate load of a crack.
This thesis found that the reinforcement ratios, prestressing stress, shear span and effective depth (as well as the concrete strength in lesser amount) influence the location of the critical cross section. The experiments and models found in literature, as well as the results found using the plasticity approach, indicate that the critical cross section for prestressed beams may be moved from 1d to 1.5d away from intermediate supports. However, due to the limitations and assumptions of the models it would not be safe to apply this change without further validation. It is therefore recommended that experiments are done on prestressed continuous beams with low amounts of shear reinforcement before any changes are made to the location of the control section. ... Read more

This study investigates the differences in shear behaviour between reinforced beams made of slag-based alkali-activated concrete (AAC) and Portland cement concrete (PCC), considering the effects of material properties, age, shrinkage, and strength class. A series of tests were conducted to analyze tensile strength, elastic modulus, autogenous and drying shrinkage, and their impact on shear performance over a period of 28 days to 6 months.

Results indicate that AAC mixtures exhibit lower tensile strength and elastic modulus compared to PCC mixtures, with the highest strength class (C50) of AAC showing an unexpected reduction in these properties over time. Additionally, AAC mixtures demonstrated significantly higher autogenous and drying shrinkage, with the S-AAC-C50 mixture exhibiting up to three times the shrinkage of its PCC counterpart. The increased shrinkage likely contributed to the development of micro-cracks, which may affect long-term performance.

Despite reductions in stiffness and tensile capacity, AAC mixtures showed a greater increase in crack stabilization stage, associated with aggregate interlock, dowel action, and residual tensile stress, leading to an improved ultimate shear failure capacity over time. The S-AAC-C30 and S-AAC-C50 mixtures exhibited increases of +83% and +38% in the crack stabilization stage, respectively, compared to +46% and −24% for PCC mixtures. This suggests that while AAC exhibits lower initial mechanical properties, its shear capacity benefits from an extended crack stabilization stage.

Overall, the study concludes that while AAC experiences higher shrinkage and a reduction in tensile strength and stiffness over time, its shear behavior is enhanced due to an extended crack stabilization mechanism. However, the exact role of shrinkage and its long-term implications remain unclear and require further investigation. ... 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

In the 1960s a large natural gas field was discovered in the Dutch province of Groningen, in the northern part of the Netherlands. Due to gas extraction, localised earthquakes started occurring in the 1990s. In this part of the country large numbers of buildings are constructed using unreinforced masonry (URM). Damage due to seismic activity in the region poses a threat to the structural integrity of existing masonry structures, as these buildings were never designed to withstand seismic loading. Among others, an intervention method that was considered was retrofitting with bed joint reinforced repointing. This is an attractive solution, as it is already often used in strengthening of masonry structures against settlement-induced damage, especially for heritage structures, as it does not affect the aesthetics of the structure. Furthermore, since this reinforcing technique is already applied to limit damage due to ground settlements, it is an attractive potential solution to counter damage due to seismic loading, as it does not require additional funding. However, not much research is available on the performance of existing masonry structures retrofitted with bed joint reinforced repointing, considering both the effect of ground settlements and seismic loading conditions. To investigate the added benefit of bed joint reinforcement, used to counteract seismic-induced damage, nonlinear finite element analyses, of a case study of a typical masonry farmhouse in the Groningen region, were performed. The masonry farmhouse was modelled as a façade, meaning no out-of-plane failure could occur. In this research, an orthotropic continuum model called the engineering masonry model (EMM) was adopted. The used numerical modelling approach was first validated against in-plane experimental tests of unstrengthened and strengthened masonry walls, performed at TU Delft previously. For the façade, various cases were analysed: an unstrengthened façade, strengthened façades, using various peak ground velocities and a partially reinforced masonry façade. The results were analysed in terms of crack widths, crack patterns and damage values, which were developed previously by others. The numerical results showed that limited damage is caused by an earthquake with the expected seismic load (PGV of 64mm/s). It was found that retrofitting with bed joint reinforced repointing after the settlement had already occurred, did not greatly increase the structural performance of this type of farmhouse façade, as most of the damage was already formed at the end of the settlement loading phase. Since the damage due to seismic loading is so small, it was therefore not recommended to strengthen this type of façade with bed joint reinforcement purely against seismic-induced damage, as the added benefit is small. However, since this strengthening technique is often applied already for strengthening against only ground settlements, it could provide a minor benefit during seismic loading, as a side effect. Amplification of the seismic load by a factor 1.5 showed only a limited increase in damage in the strengthened façade, compared to the numerical model using the expected load, while the reinforcement was significantly more activated. However, damage quickly ramped up when the seismic load is amplified by a factor 2. In this numerical model failure of the masonry façade is even observed. The numerical results of the façade with partially reinforced masonry showed a significant reduction in damage, since the bed joint reinforcement now also resisted the action of settlement loading, which is one of the most sensitive parameters of the considered façade. Since this numerical model simulates the case in which the bed joint reinforcement is applied during the construction phase, it was concluded that use of bed joint reinforcement would be beneficial for future masonry constructions. ... Read more

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

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

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

his master’s thesis investigates the design and structural behavior of Steel-Concrete-Steel (SCS) composite immersed tunnels, addressing challenges posed by traditional reinforced concrete designs. These challenges - limitations in weight, constructability, and long-term durability, particularly in deep-water environments - are exacerbated by the increasing demand for larger capacity tunnels and the need for efficient, sustainable construction methods. This research explores the impact of construction-induced irregularities, such as interface gaps and shear connector deformation, on the load-carrying capacity and overall performance of SCS tunnels. The study focuses on how irregularities produced during different construction phases affect both the local and global structural behavior of the composite cross-section. The research approach involves four distinct stages. First, a thorough examination of existing literature provides a foundation of knowledge regarding immersed composite tunnels, encompassing material properties, construction stages, and manufacturing processes. Second, a detailed SCS composite immersed tunnel design is developed, incorporating findings from a reinforced concrete tunnel case study to inform geometry and material selection. Third, numerical analysis using DIANA software is conducted. This includes 2D finite element modeling (FEM) of an SCS composite beam and a 2D FEM of the complete SCS cross-section to investigate the interaction between steel plates and concrete core under various interface conditions (strong bond versus slip) and imperfections (gaps, reduced shear connector effectiveness). Both linear elastic and nonlinear material behavior are considered. The findings highlight the critical role of horizontal interface connections and the nonlinear behavior of concrete in determining the overall load-carrying capacity and stability of SCS tunnels. The primary load bearing mechanism identified is the compressive strut within the concrete core; however, the study reveals that the structure’s failure is consistently initiated by the failure of this compressive strut, due to crushing under load. This failure mode underscores the limitations of traditional composite theory design methods and highlights the importance of the strut - and - tie model for more accurate design approaches. Construction imperfections significantly impact structural performance: strong interface connections are crucial for effective load transfer, while webs (vertical steel plates) enhance stability. The research concludes with recommendations to improve design practices, emphasizing the importance of strong horizontal connections and careful construction to maintain compressive strut integrity and avoid premature failure. ... Read more

Due to the Netherlands' topography and geology, many regions have weak soil resistance, causing numerous buildings to experience settlements from subsidence processes, with masonry structures being the most commonly affected. In these buildings, damage typically appears as cracks and deformations, indicating the foundation’s inability to support the structure. To enhance decision-making and the engineering of effective countermeasures in these scenarios, accurate and reliable building assessments are needed to predict the expected damage based on the amount of soil deformations. This thesis, therefore, aims to evaluate the capabilities of a set of state-of-the-art damage assessment methods. These methods have been applied to a case study, with their results benchmarked against evidence from a Building Foundation Assessment report, where recorded damage features were used to evaluate the accuracy and characteristics of each assessment method.
The study began with a Visual Assessment using a Decision Diagnostic Support Tool to analyze damage features and hypothesize the causes of the building's behavior. This was followed by an Empirical Assessment, applying empirical limits to relate expected damage to Subsidence-Related Intensity (SRI) parameters. Next, an Analytical Assessment used the Limit Tensile Strain Method (LTSM) to approximate building deformations, treating it as a linear-elastic isotropic masonry beam and correlating strain estimates to damage levels. Finally, a 2D Finite Element Analysis (FEA) using a continuum crack-modelling approach was conducted on the most damaged wall to more accurately reproduce the crack widths, crack locations and the behaviour of the wall.
The results show that while the building’s damage state can be approximated with reasonable accuracy, challenges remain in predicting specific damage features. The visual assessment successfully identified the building’s underlying mechanism. Empirical and analytical methods accurately predicted damage levels in 5 out of 6 walls, proving to be efficient assessment techniques. The 2D Finite Element Analysis (FEA) successfully simulated the crack pattern on Wall 2 with a Root Mean Square Error (RMSE) of +1 Ψ or +4.7mm against the maximum mean crack widths and reproduced 5 out of 7 cracks with similar characteristics. Additionally, FEA results showed that mesh sizes of 200, 100, and 50 mm made results deviate by σ = 0.33 Ψ and σCWmax = 2.3mm, with observable changes in crack shapes in EMM models.
To address the slight deviations in the less accurate analysis of the outer leaf, primarily driven by conservative crack width estimates, a Bayesian Optimization procedure was used on the outer leaf models to identify the optimal set of material parameters that minimized the discrepancy between the damage state of the results and the target damage level in the case study.
The implementation of the approach demonstrated sufficient efficiency in identifying the optimal set of parameters, despite the computational expense of the Finite Element models. The procedure’s effectiveness varied across models with it significantly reducing damage levels in the Engineering Masonry Model (EMM) variations but showed more limited improvements in the Total Strain Crack Model (TSCM). Additionally, the approach allowed for an investigation into the influence of material properties, revealing that Young's Modulus and tensile strength were the most influential parameters across both models. Furthermore, the results indicated that the influence of material parameters is highly non-linear, meaning changes in material properties do not always lead to predictable outcomes. Instead, specific combinations of parameters had a greater impact on reducing damage, demonstrating the complex interplay between material properties particularly in the EMM model variant.
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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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Dit onderzoek richt zich op het verminderen van trillingshinder in CLT- en betongebouwen, zodat ze voldoen aan de richtlijnen en er meer naast het spoor gebouwd kan worden. De centrale vraag van het onderzoek is hoe specifieke ontwerpmaatregelen kunnen leiden tot een vermindering van trillingshinder in overeenstemming met de richtlijnen. Een voorspellingsmethode is ontwikkeld om trillingshinder te voorspellen op basis van trein-geïnduceerde trillingen, waarbij voorwaarden gesteld worden aan de trilling en het frequentiespectrum. Ontwerpmaatregelen zijn bepaald voor zowel CLT (variërende dikte, totale vloerdikte, overspanning, permanente belasting) als beton (variërende vloer- en wanddikte, overspanning, stramienconfiguraties, starre vloerverbindingen). Analyse toonde aan dat ontwerpmaatregelen met betrekking tot vloer- en wanddikte en overspanning het meeste effect hadden op de eigenfrequentie van de vloer. De methode omvatte ook het gebruik van een eindig elementen model voor dynamische analyses, waaronder een frequentieresponsanalyse en een lineaire tijdsafhankelijke analyse. De methode werd toegepast op een casus in Arnhem en vergeleken met de SBR richtlijn-B voor het bepalen van hinder voor personen in gebouwen gedurende de nachtperiode. De methode bleek effectief in het voorspellen van trillingshinder bij verschillende ontwerpmaatregelen, hoewel er een onderschatting was bij maatregelen met resonantiepieken rond 10 Hz en 12 Hz. Voor zowel het CLT-model als de betonmodellen waren vergroting van de overspanning en toepassing van doorlopende tussenwanden effectieve ontwerpmaatregelen om aan de richtlijnen te voldoen. Verder onderzoek op meerdere locaties wordt aanbevolen, waarbij het gebruik van een spectrum met de volledige frequentie-inhoud van trein-geïnduceerde trillingen wordt aanbevolen en het middelen van de frequentie-inhoud wordt afgeraden. ... Read more

The main motive for this research was to study the behaviour of quay walls when there is an uneven pile foundation present. This means that the number of piles varies in the thickness of the quay wall along the length. The inspiration came from the failure of the Grimburgwal (Amsterdam, the Netherlands) that collapsed in 2020, which had a length of 65 meters, according to Korff et al. (2021). Korff et al. (2021) reported that the main failure mechanisms that are considered in the case of the Grimburgwal, is the deformation of the piles due to horizontal bending, in the section where there were only two instead of three rows of piles present in the thickness of the wall.

A 2D model with a length of 22.5 meters in the longitudinal direction (along the length of the quay) wall is used in this research, to study the influence of the uneven pile foundation in the thickness of the wall. The quay wall’s out-of-plane behaviour is not considered. The masonry and timber floor are modelled with linear plane stress elements. An interface condition is used to model the interaction between masonry and the timber floor. The longitudinal support beams and kespen are modelled as one element. The piles are modelled as equivalent translational springs that are evenly distributed in the longitudinal direction. In the central area, one spring represents two piles in the cross-section, while the rest of the springs represent three piles. After the application of the deadweight of masonry and timber, a uniform distributed load was used on top of the model to cause settlement of the piles and wall. The dilatation joint was modelled with a nonlinear interface with a high dummy stiffness and no tension, and with a gap of one millimeter.

If the length of the section with two rows of piles is increased, the capacity of the wall reduces. The cracks at the bottom of the masonry, still do not increase significantly if the length of the length of the section with two rows of piles is increased, but it does take less load to generate the same cracks. The boundary conditions also play a large role in the distribution of forces, since it is seen that the piles near the dilatation joint are less critical than the piles near the constrained edge. In the end, this model does give information on how the forces in the piles distribute and how the piles settle, before both brittle and ductile failure of the piles occurs and cracking within the model. However, it should be kept in mind that the model that is considered is a 2D model, whereas the problem of a quay wall is a 3D problem, so the results are not expected to be accurate.
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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

Masonry arch bridges have been around for centuries and are, in the Netherlands, mostly located in historical city centres. As the axle loads of vehicles passing these bridges have increased over the years, the need to re-evaluate the structural safety of these bridges has increases. To do so, different techniques have been developed. However, assumptions had to be made due to limited computational power and lack of knowledge regarding the actual behaviour of masonry. Over the years, the computational power has increased, making it possible to perform more advanced analysis and describe the behaviour of complex materials. Despite this increase, a conservative approach is still used to determine the safety of masonry arch bridges. When it is not sure whether the bridge is safe enough, the bridge is immediately strengthened or a weight restriction is applied, without calculations of the bridges actual capacity. As these interventions could be costly or cause issues with the supply of goods to the city, it is needed to find a better approach and understanding of the actual behaviour of masonry arch bridges. Therefore this study addresses the following research question:
What is the role of constitutive models on simulating the structural behaviour of masonry arch bridges?
In order to formulate an answer to the question, the behaviour of masonry, masonry arch bridges and soils have been investigated first. The investigation shows which function each part of a masonry arch bridge fulfils and which failure modes are expected to occur. When a masonry arch bridge is loaded, the backfill spreads the load and transfers this to the masonry arch. Due to this load, the arch will deform. This deformation is, however, restricted by the backfill. This interaction between the backfill and the masonry arch makes the behaviour of these types of structures a complex structural-geotechnical problem.
For masonry arch bridges, the most common failure mode is the formation of a four hinge mechanism, therefore this study focusses on modelling the behaviour of the masonry arch. Alongside the behaviour of the materials, the development in numerical tools is investigated as well. Doing so, it can be determined what assumptions have been made in the past and what the shortcomings of the approaches are. With the combined knowledge, it is possible to select different material models that can be used for masonry arch bridges. Three different models were created, two macro models and a micro model. The two macro models are both total-strain based models, where one is described by an isotropic - and one with an anisotropic material model, the so called “Total strain crack” and “Engineering masonry” model, respectively. The macro models consider the masonry as a continuum, whereas the micro model distinguishes between units and joints.
To validate the numerical models, test results are needed. As the study focuses on modelling the masonry arch, the different models are first compared to the results of a test on just a masonry arch. The chosen test was performed at the University of Minho in Portugal; a masonry arch was created and, in a displacement control manner, loaded until failure. Prior to performing the tests, the materials were first tested and their properties accurately reported, which is very useful when making a numerical model. After creating and comparing the results of the models and tests, it was found that the Engineering masonry and micro model show a similar shape of the force-displacement curve, while the isotropic “total strain crack” model does not. The engineering masonry and micro model are able to show the brittle failure of the arch, which was also obtained with the tests. However, this failure occurred when only two hinges were formed, where, in the test, a four hinge mechanism was formed. The numerical results do show that cracks are starting to form, however, this does not mean that it also is a hinge. Besides that, the test results show that there is still some redistribution of forces after the peak load. This is not possible when four hinges are already formed. It is expected that the, by the researchers defined, hinges are not actually hinges, but, are the points where cracks start to form. Despite this difference in hinge formation, the resulting force-displacement curves of the models are very close to those of the tests, therefore it can be stated that the used models are suitable to represent the behaviour of masonry arches.
After validating the effectiveness of the masonry material models, the modelling of the problem was extended by adding backfill. Again test results were needed to determine whether the models are also suitable to simulate the extended problem. This test was performed at the University of Salford in the United Kingdom and has been used by Wittenveen+Bos to validate other numerical programs in the past. The bridge was tested in a specially designed chamber, in such a way that plain strain conditions hold, and the load was applied at quarter span in a displacement controlled manner. The results were obtained by loading the arch beyond the peak load, with the applied force being reduced while the displacement continued to increase, which was, according to the research, when a four hinge mechanism was formed.
A negative consequence of plain strain conditions is that the engineering masonry material model was not available to be used, therefore only the “total strain crack” model and the micro model were compared. The initial results of the numerical model resulted in local failure of the soil just below the point load, which did not occur in reality. In order to eliminate this local failure, a small area below the load had to be given linear elastic properties. Although this local failure now doesn’t happen, the results still show that plastic strains develop in the backfill, as well as cracks in the masonry arch. A parametric study was conducted to determine the sensitivity of the models to small changes in material properties. This study showed that the models are most sensitive to changes in soil properties, specifically the internal friction angle. For the micro model, it even appeared that only changes in the soil properties affect the behaviour of the structure, meaning that the sliding failure in the backfill is the governing failure mechanism. In the isotropic “total strain crack” model, a lower tensile strength caused the behaviour of the structure to change drastically. It is found that this is due to Poisson’s ratio and the isotropic nature of the material model. The compressive stresses cause small lateral strains which, due to Poisson’s ratio, cause longitudinal strains. Due to the isotropic nature of the material model, a low tensile strength is assigned in this longitudinal direction, causing the arch to form an unrealistic crack or failure pattern. While in reality the tensile strength in this longitudinal direction, the brick tensile strength, is larger compared to the assigned the brick-mortar bond strength.
Eventually, it could be concluded that it is possible to model the behaviour of masonry arch bridges with great detail. However, in this study the behaviour of the backfill governed the behaviour of the structure, making it difficult to state which modelling approach should be used for the masonry arch. What can be said, is that a micro modelling approach is currently preferred. The study shows that this model is capable of mimicking the behaviour of just a masonry arch, and is less sensitive to changes is masonry properties when backfill is added compared to the isotropic “total strain crack” material model. The anisotropic “engineering masonry” model would be a good alternative, but cannot be used in plain strain conditions, yet. Further research is needed to investigate other modelling options, as a three-dimensional model. However, to fully understand the behaviour, more tests are needed. These tests should not only be focussed on the behaviour of the arch, but also on the behaviour of the backfill; and these material properties should be tested and reported extensively.
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Mining activities at the Groningen gas field are causing earthquakes which result in building damage. This has started a discussion on what type of damage is caused by earthquakes. These discussions are typical in the forensic engineering field, especially in complex cases. The problem is the lack of regulations, in terms of standardizations and uniformization.
To solve that problem, experts can be provided with an independent tool which can contribute to the investigation of the cause of building damage. The tool can help to indicate potential damage causes. This will support the findings of experts. Also, it can draw attention to overlooked damage causes.
The tool is based on relations found in a database of damage cases that have been determined earlier. The database consists of damage cases in the Groningen province. Not all available damage cases were incorporated in this thesis, because processing the damage reports to a database was a labour-intensive job. The analysed dataset consists of 1830 damage cases in 49 buildings. Experts were able to determine the cause of damage in 1180 of these damage cases, which results in a ratio of 64.4% known cases. Only the known cases where applied in the analysis. The buildings were located in seven different areas in the province of Groningen.
Each analysed damage case consists of a damage cause and a description. A description has been structured in 191 characteristics. These characteristics have been categorised into three types: building characteristics, context characteristics and damage characteristics. Building characteristics say something about the function, materials and size of the building. Context characteristics explain the sub soil, vibration sources and external forces in the surrounding of the building. Damage characteristics describe how damage is presented in terms of position, location and shape of damage.
Whether the found relations can be deployed in practice, depends on how useful those relations are. Useful is defined as reliable and meaningful. Reliable is how a found pattern performs according to a test, mostly measured in terms of accuracy or coefficient of determination. Meaningful is whether the found relations are logical to be explained by literature or plausible damage situations. The pattern recognition can introduce some relations and can provide them with a reliability value. However, if the relations are not explainable, they do not mean anything for use in practice.
The relations in these data were found by deploying pattern recognition methods. Two algorithms were utilized as a pattern recognition method: decision tree and linear regression. A decision tree algorithm splits the data into groups by applying thresholds on case characteristics. These thresholds can be made visual in a decision tree figure. Linear regression tries to obtain a target value by means of a linear relation of characteristics. Therefore, the linear regression algorithm determines the slope value of each characteristic.
Classification analyses were done with decision trees on six damage cause categories. The results of that type of analysis were capable of determining if or which damage was caused by a certain cause. Linear regression was performed in order to find regression relations where the technical attributability of a damage cause could be calculated for each case. In the more complex task of regression analysis, only three damage cause categories were suitable for finding a relation.
To determine whether damage was caused by earthquakes, earthquake load in terms of PGV is an important characteristic. Also, the age of a building and trees has a possible significant influence on the occurrence of earthquake damage, according to the found pattern. A relation between those last two characteristics and earthquake damage is not described in literature. Besides that, this decision tree pattern seems to be the most useful pattern for in practice.
Another interesting finding is that hindered deformation mostly occurred at the inside of a building. Combined with other characteristics, a pattern on this damage cause performed with the highest score in this thesis. It has an accuracy of 77%. This means that 77% of the cases in the test set were correctly predicted by the produced classification decision tree. However, the found relation with the characteristics is not always explainable or meaningful so as to be applied in practice. More conclusions of classification analysis are shown in Table 1.
<Table 1, See abstract in report>
The presented findings above are classification relations. Regression analyses were difficult to execute. A desired positive coefficient of determination (R2) could not be reached without subjective interference in the pattern recognition. The best regression result was obtained on damage caused by earthquakes. It had a R2 of 0.48. Which means that 48% of the data was describable in a linear relation. More conclusions of regression analysis are shown in Table 2.
<Table 2, See abstract in report>
It has been interesting to study the relation between characteristics and damage causes. However, the results are not of decisive importance. The building and context characteristics supported by literature were not always selected or applied properly by the pattern recognition. Also, the potential of damage characteristics was not recognized by the algorithms. Nonetheless, the results of earthquake related damage seem promising. They even indicate characteristics which may be worth investigating more closely.
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The extraction of natural gas in the northern part of the Netherlands, from the region of Groningen, has been causing human-induced seismic activities for the past several decades. This is a problem since the existing building stock in this region, which consists of mainly unreinforced masonry buildings and historical structures, are not designed to withstand seismic events due to the lack of empirical earthquake-resistant design features. Further, the combination of a soft topsoil and the gas extraction, is responsible for ground settlements which may compromise the capacity of the existing buildings.

The bed-joint reinforcement technique is a strengthening method which consists of cutting a slot in the bed-joints and installing steel bars embedded in a high-strength repair mortar. Although this strengthening method is commonly applied in the Netherlands to counteract settlement damage, limited investigations on the performance against seismic loading are available in the literature. Therefore, an experimental campaign (Licciardello et al., 2021) was conducted at Delft University of Technology in which a quasi-static cyclic in-plane test on a full scale wall was performed to characterize the performance of the bed-joint reinforcement technique. The wall featured artificially introduced cracks (pre-damage), achieved by the inclusion of plastic sheets between bricks and mortar, to account for the settlement-induced damage. Compared to the un-strengthened walls, tested in a previous experimental campaign (Korswagen et al., 2019) under similar conditions, it is observed that the bed-joint reinforcement technique can provide a significant increment in terms of displacement capacity and ductility of the wall but not in terms of the force capacity.

In this thesis, numerical simulations of both un-strengthened and strengthened walls from the experiments were performed using 2D-models and the nonlinear static analyses (monotonic and cyclic) were carried out in the finite element software DIANA. The objective of this research was to compare different numerical modeling approaches and material models to find the best suited one for simulating the in-plane seismic response of both un-strengthened and strengthened masonry walls. Moreover, the objective was also to extrapolate the experimental results to other wall configurations, which are not experimentally tested, to investigate the combined effect of the bed-joint reinforcement technique and the change in size and location of the window opening on the in-plane response of the wall (parametric study).

In the scope of this thesis, three numerical modeling approaches were investigated (Figure i). The bricks and mortar joints are modeled as one homogeneous continuum in the macro-model. On the other hand, the bricks and mortar joints are modeled separately for the continuous and detailed micro-model where interface elements are included at the brick-mortar bonds for the latter one. The discrete (simplified) micro-model was not investigated because the reinforcement bars cannot be connected to the mortar joints since they are substituted by zero-thickness interface elements. Moreover, the Discrete modeling approach of the reinforcement was used in order to simulate the pull out behavior of the bars. Cracks were modeled using the discrete cracking approach and the smeared cracking approach where the former one was used at the brick-mortar interfaces and the latter one was used for cracking in the mortar joints (micro-models) and in the masonry composite (macro-model)…

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Climate change is changing the world. Where previously efficient use of materials was mainly applied to realize cost savings, this can also help to reduce the footprint of a construction. There is a rather direct and obvious relationship between the amount of material required in a construction and its environmental impact. Of course, the environmental impact is not solely dependent on this metric, but minimizing the weight of the structure is a great starting point. This thesis focusses on minimizing the environmental impact of a welded truss bridge. In addition to the required volume of construction material, the environmental costs for the welding and conservation are also taken into account. A case study is performed on a bicycle bridge crossing a highway that is built in the Netherlands.

The thesis starts with a review of multiple methods that minimize the weight of a structure. Within the field of structural optimization, The Ground Structure Method (GSM) appears to be the most suitable method for large structures that consist of slender structural elements. Making utterly high refinements in the GSM-model will result in a structure with definitely the lowest volume possible. However, this structure will have lots of smaller and shorter elements that will require in total more welding and conservation. This will not lead to a least-environmental-impacting structure. Thus the main question arises:

Will, within the ground structure method, minimizing on the environmental impact result in a significantly different structure than a minimization on weight?

The objective function for the environmental impact consists of the three considered contributing factors: the construction material, welding and the conservation. The environmental impact for the three factors is determined with a Life Cycle Assessment (LCA). Finally, every contributing factor is unified into a single indicator value through the Environmental Cost Indicator (ECI) method.
The objective function also consists of three variables which represent: the volume of construction material, the welding volume and the surface of the structure. The volume is already known, since it is the regular GSM minimization. The welding volume can be determined through the joint-cost method, which is adding an artificial length to each member. The surface area of the structure is harder to determine. The relation of the volume of a construction element and its surface area is generally speaking non-linear. Multiple implementations were investigated. The aim is to perform the optimization on a fully connected ground structure, and so the assumption is made to make the relation between the volume and surface area linear. A circular hollow cross section with a variable radius and a constant wall thickness is implemented into the optimization method. The final objective function to minimize the ECI costs is a mixed-integer linear programming problem (MILP).

This method is tested on the established benchmark for a cantilever structure and on a case study for a bicycle bridge. The shape of the optimal structure is dependent on the amount of nodes within the design domain. The results for the cantilever structure does clearly reflect this. Depending on the amount of nodes in the design domain, the minimization of the environmental impact is decreased between 0 and 37%, while the weight is at most 2.5% higher. The difference of the environmental impact between the least-weight and least-environmental-impacting structure keeps increasing as the node density increases.
The bicycle bridge is optimized in a 2D and 3D design domain. The design domain of the bicycle bridge appeared to be too big to be solved by the MILP formulation optimization, thus the domain is reduced to a single span of the bridge. Furthermore, the amount of nodes in the design domain is limited to improve the computability of the problem. In both the 2D and 3D variant the regular minimization on weight requires only a fraction of the time to solve the problem successfully. For the 2D case there is a difference between the minimization of the weight and ECI. The number of members in the least-environmental-impacting structure is reduced by 40%, which results in a 1% lower environmental impact. The MILP could not converge properly in 4 hours in the 3D design domain. This is mainly because the model size did increase a lot compared to the 2D design domain. Going from 2D to 3D adds a third axis, which increases the amount of constraints by 50%. Likewise, the number of nodes in a 3D domain increase more rapidly than in a 2D domain.

All in all, the method is implemented successfully and validated with the cantilever structure. The proposed method will result in a structure with an equal or lower environmental impact compared to the regular least-weight minimization. However the minimization of the environmental cost with the proposed optimization method is able to solve problems with around 5,000 variables. To solve larger models successfully it is advised to either reduce the connectivity of the ground structure or to apply the joint-cost method with an LP.
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Gas extractions are responsible for mostly all induced earthquakes in the Groningen area and this leads to damage of houses and buildings and issues regarding safety. Current strengthening measurements are mostly very visible. However, this can change by using the window frame as part of the structure, particularly interesting for Dutch houses characterized by large window openings. In this thesis, the focus is on the validation of the numerical model based on experimental testing. From this, the main research question was formulated as “How can the structural window frame be modelled to agree with the experimental results, in order to assess the seismic performance for unreinforced masonry structures?”. The structural window frame is made of a timber frame, an adhesive and a double-glazing unit. The timber frame is made of hardwood on the outside and plywood on the inside. The potential of the structural window frame is researched into several numerical, experimental and design studies using DIANA 10.4. It is concluded that a specific non-linear elastic interface model for the adhesive is the best suitable model. This numerical model is used as a loading protocol for the experiments. The structural window frames have been built and tested at the TU Delft. The experimental results showed that the structural window frame behaves plastically. Concluding, the glass panels and the hardwood are not damaged however, the plywood is pinched due to the glass panel. The numerical model is adjusted to include the pinching behaviour of the inner bar to suit the experiments. The next step is the masonry model. The masonry model including the structural window frame showed an increase of 15% for the in-plane shear force capacity and a decrease of 23% for the crack width for a displacement of 4 mm, compared to the unstrengthened masonry wall. The pushover calculation showed that both the unstrengthened and strengthened masonry wall can withstand the seismic loads in Appingedam. According to assumptions, the structural window frame results in an increase of the shear force capacity of 47% for larger displacements. The ductility of the structure can be increased by increasing the effective mass to 15000 kg. However, the calculation is only valid for the assumed values, these results should not be taken too strictly. The design of the window frame can be improved by using: a stiffer timber frame, a thinner adhesive and a more sustainable design. Using a frame that is twice as stiff and strong has resulted in: similar initial behaviour, higher maximum shear force and later stabilisation of the in-plane shear force. Using a thinner adhesive than 5 mm does not result in more beneficial results. Furthermore, making only screwed connections and maintaining the structural window frame frequently could increase the lifespan of the structural window frame. The structural window frame has potential however, more numerical and experimental research should be done. ... Read more

Masonry is one of the most common building materials globally due to its ease of construction, price, durability and fire resistance. Its heterogeneity and orthotropic nature make its mechanical behaviour rather complex, highlighting the importance of an appropriate constitutive model to describe such behaviour accurately. In literature, most of the existing constitutive models for masonry fall in one of the two following categories: macro-models or micro-models. The micro-models (also called block-based models), which explicitly describe masonry's geometrical and material heterogeneities, exhibit higher accuracy but require higher numerical efforts when simulating masonry's mechanical behaviour. The macro-models (also called continuum models), which model masonry as homogeneous material and smear out the damage over the continua, are less accurate but offer a good compromise between accuracy and numerical efficiency. They are therefore used more often to simulate masonry structures. However, most of the macro-models are not capturing well the damage localization occurring along the mortar joints and the energy dissipation in the bricks and mortars. To increase the applicability of continuum models, the components' damage localization and energy dissipation should be improved. This thesis presents a homogenized constitutive model for applications on masonry structures under in-plane loading. The developed homogenized material model for masonry includes the description of shearing, tensile cracking, crushing and splitting. Inspired by the micro-mechanical models of Zucchini and Lourenço, four models were developed in this thesis to describe the different types of in-plane failure of masonry, naming: tensile failure of bed joints, horizontal shear sliding of bed joints, tensile cracking of unit, diagonal tensile cracking failure, masonry crushing failure. The first model is derived for the masonry’s pure shear behaviour, where the shear sliding failure is introduced. The second one is derived for the horizontal tensile behaviour, where the vertical tensile cracking of brick units and the vertical joints is proposed. The third one is derived for the vertical compression behaviour, where masonry crushing failure is adopted. The fourth one is coupling the failure mechanisms described in the previous three models with a novel algorithm. Additionally, the diagonal tension cracking failure and the horizontal tensile cracking of horizontal joints are incorporated in the fourth and final material model. To derive these models, first, a representative volume element (RVE) was selected for running bond wall, where the bricks are staggered by half-length of brick from the adjoining courses above and below. Each RVE consists of two-quarters of bricks connected through a bed joint, and each one is connected to a head joint on one side. For each of the models, the active internal stresses of each component (brick, bed, head or cross joint) are calculated through the compatibility and equilibrium equations resulting from the assumed deformed mechanisms. Different damage state variables are introduced for every component in the damage model, where exponential softening is assumed for tension and shear. Additionally, a Ducker-Prager yield criterion with bi-parabolic hardening is used in combination with an explicit Euler-forward algorithm to describe the elastoplastic behaviour of the material in compression. As a result, the material model’s constitutive law is obtained with the homogenization procedures after coupling the damage and plastic model together by a specific algorithm originally introduced by Zucchini and Lourenço. The constitutive equations for model 1 (shear), model 2 (tension), model 3 (compression) and model 4 (coupled) were coded successfully in MATLAB. The components’ shearing, tensile cracking, crushing and splitting failures are correctly modelled analytically with an algorithm, which can be applied to simplify the micro-mechanical model. Besides, constitutive laws of models 1 and 2 were also implemented successfully in the finite element software DIANA version 10.4 (check). The ability of the model to capture the failure of the components in shear, tensile cracking or crushing was examined through simple analytical applications. Moreover, the model was compared against experimental results from tests performed on masonry wallets under compressive loading; the model was able to predict the strength of the specimens satisfactorily. Therefore, this alternative constitutive material model can adequately simulate masonry’s behaviours with a simpler algorithm than the previous model. Meanwhile, the component’s elastic and elastoplastic behaviours can be simulated in more detail in this model, as the case that the horizontal joint is first damaged in shear and compressive splitting effects are additionally included. ... Read more

Due to the recent increase in traffic capacity requirements, the need for larger spans in immersed concrete tunnels has become a pressing matter. Although commonly used in Europe, reinforced concrete has a structural capacity limit when it comes to the transverse span length. The implementation of post-tensioning could allow for longer spans and a reduction in the overall concrete used. This technique is however rarely used in industry due to the complexity of applying it to underwater environments and the varied loading conditions an immersed tunnel element is subjected to. When implementing post-tensioned tendons, the curvature creates additional distributed loads which compensate for the high hydrostatic pressures and backfilling weight present at the final immersed stage of the tunnel. Due to the absence of these loads during the initial stages, prior to transportation, high tensile stresses are exhibited which can lead to severe cracking. Crack mitigation can be achieved by implementing permanent additional reinforcements in the opposite face of the post tensioning tendon. Additionally, another method is installing a temporary system connecting top and bottom slabs to replicate the final loading conditions. The objective of this research is to investigate the governing limitations of implementing transverse post-tensioning and evaluate when it is a structurally viable option. Using finite element modelling, a linear analysis was carried out to evaluate the behavior of the structure after implementing post-tensioning loads in the cross section and to identify the critical areas. The assumptions for the analytical moment distribution were found to overestimate the rigidity of the structure and made for larger moments at the wall-top slab connections, which were adjusted for the remaining parts of the study. An analysis into the effect of adding post-tensioning in the lower bottom slab revealed a substantial improvement in the final stage stress distribution, and was observed to be in full compression. A nonlinear analysis was used to provide insight into the global structural behaviour for both final immersed and dry dock stages. The final immersed stage exhibited linear elastic behaviour, whereas, the onset of cracking was observed at the top of midspan at the dry dock stage. In a further analysis of the critical dry dock stage, the relation between partial prestressing, curvature of post-tensioning tendons and the effects on the cracking behaviour at midspan was explored. The results showed that when maximum curvature and percentage of prestressing are simultaneously present, the crack width limit is reached. When slightly lowering either of these parameters, a substantial decrease in the amount of reinforcement is needed to mitigate these cracks. Lastly, a case study was carried out on the Fehrmanbelt Fixed Link to compare two methods to mitigate cracks at midspan in the dry dock: additional reinforcement and temporary tendons. This study found that implementing transverse post-tensioning was feasible when reducing the curvature of the tendons, reducing amount of prestressing and implementing additional reinforcement, which helped increase structural capacity of the critical areas in the dry dock stage. ... Read more